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Commit 5c3927dc authored by Greg Kroah-Hartman's avatar Greg Kroah-Hartman
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[PATCH] devfs: Remove devfs documentation from the kernel tree 

Removes the Documentaiton/filesystems/devfs/ directory
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent d8deac50
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/* -*- auto-fill -*- */
===============================================================================
Changes for patch v1
- creation of devfs
- modified miscellaneous character devices to support devfs
===============================================================================
Changes for patch v2
- bug fix with manual inode creation
===============================================================================
Changes for patch v3
- bugfixes
- documentation improvements
- created a couple of scripts (one to save&restore a devfs and the
other to set up compatibility symlinks)
- devfs support for SCSI discs. New name format is: sd_hHcCiIlL
===============================================================================
Changes for patch v4
- bugfix for the directory reading code
- bugfix for compilation with kerneld
- devfs support for generic hard discs
- rationalisation of the various watchdog drivers
===============================================================================
Changes for patch v5
- support for mounting directly from entries in the devfs (it doesn't
need to be mounted to do this), including the root filesystem.
Mounting of swap partitions also works. Hence, now if you set
CONFIG_DEVFS_ONLY to 'Y' then you won't be able to access your discs
via ordinary device nodes. Naturally, the default is 'N' so that you
can still use your old device nodes. If you want to mount from devfs
entries, make sure you use: append = "root=/dev/sd_..." in your
lilo.conf. It seems LILO looks for the device number (major&minor)
and writes that into the kernel image :-(
- support for character memory devices (/dev/null, /dev/zero, /dev/full
and so on). Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
===============================================================================
Changes for patch v6
- support for subdirectories
- support for symbolic links (created by devfs_mk_symlink(), no
support yet for creation via symlink(2))
- SCSI disc naming now cast in stone, with the format:
/dev/sd/c0b1t2u3 controller=0, bus=1, ID=2, LUN=3, whole disc
/dev/sd/c0b1t2u3p4 controller=0, bus=1, ID=2, LUN=3, 4th partition
- loop devices now appear in devfs
- tty devices, console, serial ports, etc. now appear in devfs
Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
- bugs with mounting devfs-only devices now fixed
===============================================================================
Changes for patch v7
- SCSI CD-ROMS, tapes and generic devices now appear in devfs
===============================================================================
Changes for patch v8
- bugfix with no-rewind SCSI tapes
- RAMDISCs now appear in devfs
- better cleaning up of devfs entries created by various modules
- interface change to <devfs_register>
===============================================================================
Changes for patch v9
- the v8 patch was corrupted somehow, which would affect the patch for
linux/fs/filesystems.c
I've also fixed the v8 patch file on the WWW
- MetaDevices (/dev/md*) should now appear in devfs
===============================================================================
Changes for patch v10
- bugfix in meta device support for devfs
- created this ChangeLog file
- added devfs support to the floppy driver
- added support for creating sockets in a devfs
===============================================================================
Changes for patch v11
- added DEVFS_FL_HIDE_UNREG flag
- incorporated better patch for ttyname() in libc 5.4.43 from H.J. Lu.
- interface change to <devfs_mk_symlink>
- support for creating symlinks with symlink(2)
- parallel port printer (/dev/lp*) now appears in devfs
===============================================================================
Changes for patch v12
- added inode check to <devfs_fill_file> function
- improved devfs support when mounting from devfs
- added call to <<release>> operation when removing swap areas on
devfs devices
- increased NR_SUPER to 128 to support large numbers of devfs mounts
(for chroot(2) gaols)
- fixed bug in SCSI disc support: was generating incorrect minors if
SCSI ID's did not start at 0 and increase by 1
- support symlink traversal when mounting root
===============================================================================
Changes for patch v13
- added devfs support to soundcard driver
Thanks to Eric Dumas <dumas@linux.eu.org> and
C. Scott Ananian <cananian@alumni.princeton.edu>
- added devfs support to the joystick driver
- loop driver now has it's own subdirectory "/dev/loop/"
- created <devfs_get_flags> and <devfs_set_flags> functions
- fix problem with SCSI disc compatibility names (sd{a,b,c,d,e,f})
which assumes ID's start at 0 and increase by 1. Also only create
devfs entries for SCSI disc partitions which actually exist
Show new names in partition check
Thanks to Jakub Jelinek <jj@sunsite.ms.mff.cuni.cz>
===============================================================================
Changes for patch v14
- bug fix in floppy driver: would not compile without
CONFIG_DEVFS_FS='Y'
Thanks to Jurgen Botz <jbotz@nova.botz.org>
- bug fix in loop driver
Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
- do not create devfs entries for printers not configured
Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
- do not create devfs entries for serial ports not present
Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
- ensure <tty_register_devfs> is exported from tty_io.c
Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
- allow unregistering of devfs symlink entries
- fixed bug in SCSI disc naming introduced in last patch version
===============================================================================
Changes for patch v15
- ported to kernel 2.1.81
===============================================================================
Changes for patch v16
- created <devfs_set_symlink_destination> function
- moved DEVFS_SUPER_MAGIC into header file
- added DEVFS_FL_HIDE flag
- created <devfs_get_maj_min>
- created <devfs_get_handle_from_inode>
- fixed bugs in searching by major&minor
- changed interface to <devfs_unregister>, <devfs_fill_file> and
<devfs_find_handle>
- fixed inode times when symlink created with symlink(2)
- change tty driver to do auto-creation of devfs entries
Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
- fixed bug in genhd.c: whole disc (non-SCSI) was not registered to
devfs
- updated libc 5.4.43 patch for ttyname()
===============================================================================
Changes for patch v17
- added CONFIG_DEVFS_TTY_COMPAT
Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
- bugfix in devfs support for drivers/char/lp.c
Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
- clean up serial driver so that PCMCIA devices unregister correctly
Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
- fixed bug in genhd.c: whole disc (non-SCSI) was not registered to
devfs [was missing in patch v16]
- updated libc 5.4.43 patch for ttyname() [was missing in patch v16]
- all SCSI devices now registered in /dev/sg
- support removal of devfs entries via unlink(2)
===============================================================================
Changes for patch v18
- added floppy/?u720 floppy entry
- fixed kerneld support for entries in devfs subdirectories
- incorporated latest patch for ttyname() in libc 5.4.43 from H.J. Lu.
===============================================================================
Changes for patch v19
- bug fix when looking up unregistered entries: kerneld was not called
- fixes for kernel 2.1.86 (now requires 2.1.86)
===============================================================================
Changes for patch v20
- only create available floppy entries
Thanks to Andrzej Krzysztofowicz <ankry@green.mif.pg.gda.pl>
- new IDE naming scheme following SCSI format (i.e. /dev/id/c0b0t0u0p1
instead of /dev/hda1)
Thanks to Andrzej Krzysztofowicz <ankry@green.mif.pg.gda.pl>
- new XT disc naming scheme following SCSI format (i.e. /dev/xd/c0t0p1
instead of /dev/xda1)
Thanks to Andrzej Krzysztofowicz <ankry@green.mif.pg.gda.pl>
- new non-standard CD-ROM names (i.e. /dev/sbp/c#t#)
Thanks to Andrzej Krzysztofowicz <ankry@green.mif.pg.gda.pl>
- allow symlink traversal when mounting the root filesystem
- Create entries for MD devices at MD init
Thanks to Christophe Leroy <christophe.leroy5@capway.com>
===============================================================================
Changes for patch v21
- ported to kernel 2.1.91
===============================================================================
Changes for patch v22
- SCSI host number patch ("scsihosts=" kernel option)
Thanks to Andrzej Krzysztofowicz <ankry@green.mif.pg.gda.pl>
===============================================================================
Changes for patch v23
- Fixed persistence bug with device numbers for manually created
device files
- Fixed problem with recreating symlinks with different content
- Added CONFIG_DEVFS_MOUNT (mount devfs on /dev at boot time)
===============================================================================
Changes for patch v24
- Switched from CONFIG_KERNELD to CONFIG_KMOD: module autoloading
should now work again
- Hide entries which are manually unlinked
- Always invalidate devfs dentry cache when registering entries
- Support removal of devfs directories via rmdir(2)
- Ensure directories created by <devfs_mk_dir> are visible
- Default no access for "other" for floppy device
===============================================================================
Changes for patch v25
- Updates to CREDITS file and minor IDE numbering change
Thanks to Andrzej Krzysztofowicz <ankry@green.mif.pg.gda.pl>
- Invalidate devfs dentry cache when making directories
- Invalidate devfs dentry cache when removing entries
- More informative message if root FS mount fails when devfs
configured
- Fixed persistence bug with fifos
===============================================================================
Changes for patch v26
- ported to kernel 2.1.97
- Changed serial directory from "/dev/serial" to "/dev/tts" and
"/dev/consoles" to "/dev/vc" to be more friendly to new procps
===============================================================================
Changes for patch v27
- Added support for IDE4 and IDE5
Thanks to Andrzej Krzysztofowicz <ankry@green.mif.pg.gda.pl>
- Documented "scsihosts=" boot parameter
- Print process command when debugging kerneld/kmod
- Added debugging for register/unregister/change operations
- Added "devfs=" boot options
- Hide unregistered entries by default
===============================================================================
Changes for patch v28
- No longer lock/unlock superblock in <devfs_put_super> (cope with
recent VFS interface change)
- Do not automatically change ownership/protection of /dev/tty
- Drop negative dentries when they are released
- Manage dcache more efficiently
===============================================================================
Changes for patch v29
- Added DEVFS_FL_AUTO_DEVNUM flag
===============================================================================
Changes for patch v30
- No longer set unnecessary methods
- Ported to kernel 2.1.99-pre3
===============================================================================
Changes for patch v31
- Added PID display to <call_kerneld> debugging message
- Added "diread" and "diwrite" options
- Ported to kernel 2.1.102
- Fixed persistence problem with permissions
===============================================================================
Changes for patch v32
- Fixed devfs support in drivers/block/md.c
===============================================================================
Changes for patch v33
- Support legacy device nodes
- Fixed bug where recreated inodes were hidden
- New IDE naming scheme: everything is under /dev/ide
===============================================================================
Changes for patch v34
- Improved debugging in <get_vfs_inode>
- Prevent duplicate calls to <devfs_mk_dir> in SCSI layer
- No longer free old dentries in <devfs_mk_dir>
- Free all dentries for a given entry when deleting inodes
===============================================================================
Changes for patch v35
- Ported to kernel 2.1.105 (sound driver changes)
===============================================================================
Changes for patch v36
- Fixed sound driver port
===============================================================================
Changes for patch v37
- Minor documentation tweaks
===============================================================================
Changes for patch v38
- More documentation tweaks
- Fix for sound driver port
- Removed ttyname-patch (grab libc 5.4.44 instead)
- Ported to kernel 2.1.107-pre2 (loop driver fix)
===============================================================================
Changes for patch v39
- Ported to kernel 2.1.107 (hd.c hunk broke due to spelling "fixes"). Sigh
- Removed many #ifdef's, replaced with trickery in include/devfs_fs.h
===============================================================================
Changes for patch v40
- Fix for sound driver port
- Limit auto-device numbering to majors 128 to 239
===============================================================================
Changes for patch v41
- Fixed inode times persistence problem
===============================================================================
Changes for patch v42
- Ported to kernel 2.1.108 (drivers/scsi/hosts.c hunk broke)
===============================================================================
Changes for patch v43
- Fixed spelling in <devfs_readlink> debug
- Fixed bug in <devfs_setup> parsing "dilookup"
- More #ifdef's removed
- Supported Sparc keyboard (/dev/kbd)
- Supported DSP56001 digital signal processor (/dev/dsp56k)
- Supported Apple Desktop Bus (/dev/adb)
- Supported Coda network file system (/dev/cfs*)
===============================================================================
Changes for patch v44
- Fixed devfs inode leak when manually recreating inodes
- Fixed permission persistence problem when recreating inodes
===============================================================================
Changes for patch v45
- Ported to kernel 2.1.110
===============================================================================
Changes for patch v46
- Ported to kernel 2.1.112-pre1
- Removed harmless "unused variable" compiler warning
- Fixed modes for manually recreated device nodes
===============================================================================
Changes for patch v47
- Added NULL devfs inode warning in <devfs_read_inode>
- Force all inode nlink values to 1
===============================================================================
Changes for patch v48
- Added "dimknod" option
- Set inode nlink to 0 when freeing dentries
- Added support for virtual console capture devices (/dev/vcs*)
Thanks to Dennis Hou <smilax@mindmeld.yi.org>
- Fixed modes for manually recreated symlinks
===============================================================================
Changes for patch v49
- Ported to kernel 2.1.113
===============================================================================
Changes for patch v50
- Fixed bugs in recreated directories and symlinks
===============================================================================
Changes for patch v51
- Improved robustness of rc.devfs script
Thanks to Roderich Schupp <rsch@experteam.de>
- Fixed bugs in recreated device nodes
- Fixed bug in currently unused <devfs_get_handle_from_inode>
- Defined new <devfs_handle_t> type
- Improved debugging when getting entries
- Fixed bug where directories could be emptied
- Ported to kernel 2.1.115
===============================================================================
Changes for patch v52
- Replaced dummy .epoch inode with .devfsd character device
- Modified rc.devfs to take account of above change
- Removed spurious driver warning messages when CONFIG_DEVFS_FS=n
- Implemented devfsd protocol revision 0
===============================================================================
Changes for patch v53
- Ported to kernel 2.1.116 (kmod change broke hunk)
- Updated Documentation/Configure.help
- Test and tty pattern patch for rc.devfs script
Thanks to Roderich Schupp <rsch@experteam.de>
- Added soothing message to warning in <devfs_d_iput>
===============================================================================
Changes for patch v54
- Ported to kernel 2.1.117
- Fixed default permissions in sound driver
- Added support for frame buffer devices (/dev/fb*)
===============================================================================
Changes for patch v55
- Ported to kernel 2.1.119
- Use GCC extensions for structure initialisations
- Implemented async open notification
- Incremented devfsd protocol revision to 1
===============================================================================
Changes for patch v56
- Ported to kernel 2.1.120-pre3
- Moved async open notification to end of <devfs_open>
===============================================================================
Changes for patch v57
- Ported to kernel 2.1.121
- Prepended "/dev/" to module load request
- Renamed <call_kerneld> to <call_kmod>
- Created sample modules.conf file
===============================================================================
Changes for patch v58
- Fixed typo "AYSNC" -> "ASYNC"
===============================================================================
Changes for patch v59
- Added open flag for files
===============================================================================
Changes for patch v60
- Ported to kernel 2.1.123-pre2
===============================================================================
Changes for patch v61
- Set i_blocks=0 and i_blksize=1024 in <devfs_read_inode>
===============================================================================
Changes for patch v62
- Ported to kernel 2.1.123
===============================================================================
Changes for patch v63
- Ported to kernel 2.1.124-pre2
===============================================================================
Changes for patch v64
- Fixed Unix98 pty support
- Increased buffer size in <get_partition_list> to avoid crash and
burn
===============================================================================
Changes for patch v65
- More Unix98 pty support fixes
- Added test for empty <<name>> in <devfs_find_handle>
- Renamed <generate_path> to <devfs_generate_path> and published
- Created /dev/root symlink
Thanks to Roderich Schupp <rsch@ExperTeam.de>
with further modifications by me
===============================================================================
Changes for patch v66
- Yet more Unix98 pty support fixes (now tested)
- Created <devfs_get_fops>
- Support media change checks when CONFIG_DEVFS_ONLY=y
- Abolished Unix98-style PTY names for old PTY devices
===============================================================================
Changes for patch v67
- Added inline declaration for dummy <devfs_generate_path>
- Removed spurious "unable to register... in devfs" messages when
CONFIG_DEVFS_FS=n
- Fixed misc. devices when CONFIG_DEVFS_FS=n
- Limit auto-device numbering to majors 144 to 239
===============================================================================
Changes for patch v68
- Hide unopened virtual consoles from directory listings
- Added support for video capture devices
- Ported to kernel 2.1.125
===============================================================================
Changes for patch v69
- Fix for CONFIG_VT=n
===============================================================================
Changes for patch v70
- Added support for non-OSS/Free sound cards
===============================================================================
Changes for patch v71
- Ported to kernel 2.1.126-pre2
===============================================================================
Changes for patch v72
- #ifdef's for CONFIG_DEVFS_DISABLE_OLD_NAMES removed
===============================================================================
Changes for patch v73
- CONFIG_DEVFS_DISABLE_OLD_NAMES replaced with "nocompat" boot option
- CONFIG_DEVFS_BOOT_OPTIONS removed: boot options always available
===============================================================================
Changes for patch v74
- Removed CONFIG_DEVFS_MOUNT and "mount" boot option and replaced with
"nomount" boot option
- Documentation updates
- Updated sample modules.conf
===============================================================================
Changes for patch v75
- Updated sample modules.conf
- Remount devfs after initrd finishes
- Ported to kernel 2.1.127
- Added support for ISDN
Thanks to Christophe Leroy <christophe.leroy5@capway.com>
===============================================================================
Changes for patch v76
- Updated an email address in ChangeLog
- CONFIG_DEVFS_ONLY replaced with "only" boot option
===============================================================================
Changes for patch v77
- Added DEVFS_FL_REMOVABLE flag
- Check for disc change when listing directories with removable media
devices
- Use DEVFS_FL_REMOVABLE in sd.c
- Ported to kernel 2.1.128
===============================================================================
Changes for patch v78
- Only call <scan_dir_for_removable> on first call to <devfs_readdir>
- Ported to kernel 2.1.129-pre5
- ISDN support improvements
Thanks to Christophe Leroy <christophe.leroy5@capway.com>
===============================================================================
Changes for patch v79
- Ported to kernel 2.1.130
- Renamed miscdevice "apm" to "apm_bios" to be consistent with
devices.txt
===============================================================================
Changes for patch v80
- Ported to kernel 2.1.131
- Updated <devfs_rmdir> for VFS change in 2.1.131
===============================================================================
Changes for patch v81
- Fixed permissions on /dev/ptmx
===============================================================================
Changes for patch v82
- Ported to kernel 2.1.132-pre4
- Changed initial permissions on /dev/pts/*
- Created <devfs_mk_compat>
- Added "symlinks" boot option
- Changed devfs_register_blkdev() back to register_blkdev() for IDE
- Check for partitions on removable media in <devfs_lookup>
===============================================================================
Changes for patch v83
- Fixed support for ramdisc when using string-based root FS name
- Ported to kernel 2.2.0-pre1
===============================================================================
Changes for patch v84
- Ported to kernel 2.2.0-pre7
===============================================================================
Changes for patch v85
- Compile fixes for driver/sound/sound_common.c (non-module) and
drivers/isdn/isdn_common.c
Thanks to Christophe Leroy <christophe.leroy5@capway.com>
- Added support for registering regular files
- Created <devfs_set_file_size>
- Added /dev/cpu/mtrr as an alternative interface to /proc/mtrr
- Update devfs inodes from entries if not changed through FS
===============================================================================
Changes for patch v86
- Ported to kernel 2.2.0-pre9
===============================================================================
Changes for patch v87
- Fixed bug when mounting non-devfs devices in a devfs
===============================================================================
Changes for patch v88
- Fixed <devfs_fill_file> to only initialise temporary inodes
- Trap for NULL fops in <devfs_register>
- Return -ENODEV in <devfs_fill_file> for non-driver inodes
- Fixed bug when unswapping non-devfs devices in a devfs
===============================================================================
Changes for patch v89
- Switched to C data types in include/linux/devfs_fs.h
- Switched from PATH_MAX to DEVFS_PATHLEN
- Updated Documentation/filesystems/devfs/modules.conf to take account
of reverse scanning (!) by modprobe
- Ported to kernel 2.2.0
===============================================================================
Changes for patch v90
- CONFIG_DEVFS_DISABLE_OLD_TTY_NAMES replaced with "nottycompat" boot
option
- CONFIG_DEVFS_TTY_COMPAT removed: existing "symlinks" boot option now
controls this. This means you must have libc 5.4.44 or later, or a
recent version of libc 6 if you use the "symlinks" option
===============================================================================
Changes for patch v91
- Switch from <devfs_mk_symlink> to <devfs_mk_compat> in
drivers/char/vc_screen.c to fix problems with Midnight Commander
===============================================================================
Changes for patch v92
- Ported to kernel 2.2.2-pre5
===============================================================================
Changes for patch v93
- Modified <sd_name> in drivers/scsi/sd.c to cope with devices that
don't exist (which happens with new RAID autostart code printk()s)
===============================================================================
Changes for patch v94
- Fixed bug in joystick driver: only first joystick was registered
===============================================================================
Changes for patch v95
- Fixed another bug in joystick driver
- Fixed <devfsd_read> to not overrun event buffer
===============================================================================
Changes for patch v96
- Ported to kernel 2.2.5-2
- Created <devfs_auto_unregister>
- Fixed bugs: compatibility entries were not unregistered for:
loop driver
floppy driver
RAMDISC driver
IDE tape driver
SCSI CD-ROM driver
SCSI HDD driver
===============================================================================
Changes for patch v97
- Fixed bugs: compatibility entries were not unregistered for:
ALSA sound driver
partitions in generic disc driver
- Don't return unregistred entries in <devfs_find_handle>
- Panic in <devfs_unregister> if entry unregistered
- Don't panic in <devfs_auto_unregister> for duplicates
===============================================================================
Changes for patch v98
- Don't unregister already unregistered entries in <unregister>
- Register entry in <sd_detect>
- Unregister entry in <sd_detach>
- Changed to <devfs_*register_chrdev> in drivers/char/tty_io.c
- Ported to kernel 2.2.7
===============================================================================
Changes for patch v99
- Ported to kernel 2.2.8
- Fixed bug in drivers/scsi/sd.c when >16 SCSI discs
- Disable warning messages when unable to read partition table for
removable media
===============================================================================
Changes for patch v100
- Ported to kernel 2.3.1-pre5
- Added "oops-on-panic" boot option
- Improved debugging in <devfs_register> and <devfs_unregister>
- Register entry in <sr_detect>
- Unregister entry in <sr_detach>
- Register entry in <sg_detect>
- Unregister entry in <sg_detach>
- Added support for ALSA drivers
===============================================================================
Changes for patch v101
- Ported to kernel 2.3.2
===============================================================================
Changes for patch v102
- Update serial driver to register PCMCIA entries
Thanks to Roch-Alexandre Nomine-Beguin <roch@samarkand.infini.fr>
- Updated an email address in ChangeLog
- Hide virtual console capture entries from directory listings when
corresponding console device is not open
===============================================================================
Changes for patch v103
- Ported to kernel 2.3.3
===============================================================================
Changes for patch v104
- Added documentation for some functions
- Added "doc" target to fs/devfs/Makefile
- Added "v4l" directory for video4linux devices
- Replaced call to <devfs_unregister> in <sd_detach> with call to
<devfs_register_partitions>
- Moved registration for sr and sg drivers from detect() to attach()
methods
- Register entries in <st_attach> and unregister in <st_detach>
- Work around IDE driver treating CD-ROM as gendisk
- Use <sed> instead of <tr> in rc.devfs
- Updated ToDo list
- Removed "oops-on-panic" boot option: now always Oops
===============================================================================
Changes for patch v105
- Unregister SCSI host from <scsi_host_no_list> in <scsi_unregister>
Thanks to Zoltn Bszrmnyi <zboszor@mail.externet.hu>
- Don't save /dev/log in rc.devfs
- Ported to kernel 2.3.4-pre1
===============================================================================
Changes for patch v106
- Fixed silly typo in drivers/scsi/st.c
- Improved debugging in <devfs_register>
===============================================================================
Changes for patch v107
- Added "diunlink" and "nokmod" boot options
- Removed superfluous warning message in <devfs_d_iput>
===============================================================================
Changes for patch v108
- Remove entries when unloading sound module
===============================================================================
Changes for patch v109
- Ported to kernel 2.3.6-pre2
===============================================================================
Changes for patch v110
- Took account of change to <d_alloc_root>
===============================================================================
Changes for patch v111
- Created separate event queue for each mounted devfs
- Removed <devfs_invalidate_dcache>
- Created new ioctl()s for devfsd
- Incremented devfsd protocol revision to 3
- Fixed bug when re-creating directories: contents were lost
- Block access to inodes until devfsd updates permissions
===============================================================================
Changes for patch v112
- Modified patch so it applies against 2.3.5 and 2.3.6
- Updated an email address in ChangeLog
- Do not automatically change ownership/protection of /dev/tty<n>
- Updated sample modules.conf
- Switched to sending process uid/gid to devfsd
- Renamed <call_kmod> to <try_modload>
- Added DEVFSD_NOTIFY_LOOKUP event
- Added DEVFSD_NOTIFY_CHANGE event
- Added DEVFSD_NOTIFY_CREATE event
- Incremented devfsd protocol revision to 4
- Moved kernel-specific stuff to include/linux/devfs_fs_kernel.h
===============================================================================
Changes for patch v113
- Ported to kernel 2.3.9
- Restricted permissions on some block devices
===============================================================================
Changes for patch v114
- Added support for /dev/netlink
Thanks to Dennis Hou <smilax@mindmeld.yi.org>
- Return EISDIR rather than EINVAL for read(2) on directories
- Ported to kernel 2.3.10
===============================================================================
Changes for patch v115
- Added support for all remaining character devices
Thanks to Dennis Hou <smilax@mindmeld.yi.org>
- Cleaned up netlink support
===============================================================================
Changes for patch v116
- Added support for /dev/parport%d
Thanks to Tim Waugh <tim@cyberelk.demon.co.uk>
- Fixed parallel port ATAPI tape driver
- Fixed Atari SLM laser printer driver
===============================================================================
Changes for patch v117
- Added support for COSA card
Thanks to Dennis Hou <smilax@mindmeld.yi.org>
- Fixed drivers/char/ppdev.c: missing #include <linux/init.h>
- Fixed drivers/char/ftape/zftape/zftape-init.c
Thanks to Vladimir Popov <mashgrad@usa.net>
===============================================================================
Changes for patch v118
- Ported to kernel 2.3.15-pre3
- Fixed bug in loop driver
- Unregister /dev/lp%d entries in drivers/char/lp.c
Thanks to Maciej W. Rozycki <macro@ds2.pg.gda.pl>
===============================================================================
Changes for patch v119
- Ported to kernel 2.3.16
===============================================================================
Changes for patch v120
- Fixed bug in drivers/scsi/scsi.c
- Added /dev/ppp
Thanks to Dennis Hou <smilax@mindmeld.yi.org>
- Ported to kernel 2.3.17
===============================================================================
Changes for patch v121
- Fixed bug in drivers/block/loop.c
- Ported to kernel 2.3.18
===============================================================================
Changes for patch v122
- Ported to kernel 2.3.19
===============================================================================
Changes for patch v123
- Ported to kernel 2.3.20
===============================================================================
Changes for patch v124
- Ported to kernel 2.3.21
===============================================================================
Changes for patch v125
- Created <devfs_get_info>, <devfs_set_info>,
<devfs_get_first_child> and <devfs_get_next_sibling>
Added <<dir>> parameter to <devfs_register>, <devfs_mk_compat>,
<devfs_mk_dir> and <devfs_find_handle>
Work sponsored by SGI
- Fixed apparent bug in COSA driver
- Re-instated "scsihosts=" boot option
===============================================================================
Changes for patch v126
- Always create /dev/pts if CONFIG_UNIX98_PTYS=y
- Fixed call to <devfs_mk_dir> in drivers/block/ide-disk.c
Thanks to Dennis Hou <smilax@mindmeld.yi.org>
- Allow multiple unregistrations
- Created /dev/scsi hierarchy
Work sponsored by SGI
===============================================================================
Changes for patch v127
Work sponsored by SGI
- No longer disable devpts if devfs enabled (caveat emptor)
- Added flags array to struct gendisk and removed code from
drivers/scsi/sd.c
- Created /dev/discs hierarchy
===============================================================================
Changes for patch v128
Work sponsored by SGI
- Created /dev/cdroms hierarchy
===============================================================================
Changes for patch v129
Work sponsored by SGI
- Removed compatibility entries for sound devices
- Removed compatibility entries for printer devices
- Removed compatibility entries for video4linux devices
- Removed compatibility entries for parallel port devices
- Removed compatibility entries for frame buffer devices
===============================================================================
Changes for patch v130
Work sponsored by SGI
- Added major and minor number to devfsd protocol
- Incremented devfsd protocol revision to 5
- Removed compatibility entries for SoundBlaster CD-ROMs
- Removed compatibility entries for netlink devices
- Removed compatibility entries for SCSI generic devices
- Removed compatibility entries for SCSI tape devices
===============================================================================
Changes for patch v131
Work sponsored by SGI
- Support info pointer for all devfs entry types
- Added <<info>> parameter to <devfs_mk_dir> and <devfs_mk_symlink>
- Removed /dev/st hierarchy
- Removed /dev/sg hierarchy
- Removed compatibility entries for loop devices
- Removed compatibility entries for IDE tape devices
- Removed compatibility entries for SCSI CD-ROMs
- Removed /dev/sr hierarchy
===============================================================================
Changes for patch v132
Work sponsored by SGI
- Removed compatibility entries for floppy devices
- Removed compatibility entries for RAMDISCs
- Removed compatibility entries for meta-devices
- Removed compatibility entries for SCSI discs
- Created <devfs_make_root>
- Removed /dev/sd hierarchy
- Support "../" when searching devfs namespace
- Created /dev/ide/host* hierarchy
- Supported IDE hard discs in /dev/ide/host* hierarchy
- Removed compatibility entries for IDE discs
- Removed /dev/ide/hd hierarchy
- Supported IDE CD-ROMs in /dev/ide/host* hierarchy
- Removed compatibility entries for IDE CD-ROMs
- Removed /dev/ide/cd hierarchy
===============================================================================
Changes for patch v133
Work sponsored by SGI
- Created <devfs_get_unregister_slave>
- Fixed bug in fs/partitions/check.c when rescanning
===============================================================================
Changes for patch v134
Work sponsored by SGI
- Removed /dev/sd, /dev/sr, /dev/st and /dev/sg directories
- Removed /dev/ide/hd directory
- Exported <devfs_get_parent>
- Created <devfs_register_tape> and /dev/tapes hierarchy
- Removed /dev/ide/mt hierarchy
- Removed /dev/ide/fd hierarchy
- Ported to kernel 2.3.25
===============================================================================
Changes for patch v135
Work sponsored by SGI
- Removed compatibility entries for virtual console capture devices
- Removed unused <devfs_set_symlink_destination>
- Removed compatibility entries for serial devices
- Removed compatibility entries for console devices
- Do not hide entries from devfsd or children
- Removed DEVFS_FL_TTY_COMPAT flag
- Removed "nottycompat" boot option
- Removed <devfs_mk_compat>
===============================================================================
Changes for patch v136
Work sponsored by SGI
- Moved BSD pty devices to /dev/pty
- Added DEVFS_FL_WAIT flag
===============================================================================
Changes for patch v137
Work sponsored by SGI
- Really fixed bug in fs/partitions/check.c when rescanning
- Support new "disc" naming scheme in <get_removable_partition>
- Allow NULL fops in <devfs_register>
- Removed redundant name functions in SCSI disc and IDE drivers
===============================================================================
Changes for patch v138
Work sponsored by SGI
- Fixed old bugs in drivers/block/paride/pt.c, drivers/char/tpqic02.c,
drivers/net/wan/cosa.c and drivers/scsi/scsi.c
Thanks to Sergey Kubushin <ksi@ksi-linux.com>
- Fall back to major table if NULL fops given to <devfs_register>
===============================================================================
Changes for patch v139
Work sponsored by SGI
- Corrected and moved <get_blkfops> and <get_chrfops> declarations
from arch/alpha/kernel/osf_sys.c to include/linux/fs.h
- Removed name function from struct gendisk
- Updated devfs FAQ
===============================================================================
Changes for patch v140
Work sponsored by SGI
- Ported to kernel 2.3.27
===============================================================================
Changes for patch v141
Work sponsored by SGI
- Bug fix in arch/m68k/atari/joystick.c
- Moved ISDN and capi devices to /dev/isdn
===============================================================================
Changes for patch v142
Work sponsored by SGI
- Bug fix in drivers/block/ide-probe.c (patch confusion)
===============================================================================
Changes for patch v143
Work sponsored by SGI
- Bug fix in drivers/block/blkpg.c:partition_name()
===============================================================================
Changes for patch v144
Work sponsored by SGI
- Ported to kernel 2.3.29
- Removed calls to <devfs_register> from cdu31a, cm206, mcd and mcdx
CD-ROM drivers: generic driver handles this now
- Moved joystick devices to /dev/joysticks
===============================================================================
Changes for patch v145
Work sponsored by SGI
- Ported to kernel 2.3.30-pre3
- Register whole-disc entry even for invalid partition tables
- Fixed bug in mounting root FS when initrd enabled
- Fixed device entry leak with IDE CD-ROMs
- Fixed compile problem with drivers/isdn/isdn_common.c
- Moved COSA devices to /dev/cosa
- Support fifos when unregistering
- Created <devfs_register_series> and used in many drivers
- Moved Coda devices to /dev/coda
- Moved parallel port IDE tapes to /dev/pt
- Moved parallel port IDE generic devices to /dev/pg
===============================================================================
Changes for patch v146
Work sponsored by SGI
- Removed obsolete DEVFS_FL_COMPAT and DEVFS_FL_TOLERANT flags
- Fixed compile problem with fs/coda/psdev.c
- Reinstate change to <devfs_register_blkdev> in
drivers/block/ide-probe.c now that fs/isofs/inode.c is fixed
- Switched to <devfs_register_blkdev> in drivers/block/floppy.c,
drivers/scsi/sr.c and drivers/block/md.c
- Moved DAC960 devices to /dev/dac960
===============================================================================
Changes for patch v147
Work sponsored by SGI
- Ported to kernel 2.3.32-pre4
===============================================================================
Changes for patch v148
Work sponsored by SGI
- Removed kmod support: use devfsd instead
- Moved miscellaneous character devices to /dev/misc
===============================================================================
Changes for patch v149
Work sponsored by SGI
- Ensure include/linux/joystick.h is OK for user-space
- Improved debugging in <get_vfs_inode>
- Ensure dentries created by devfsd will be cleaned up
===============================================================================
Changes for patch v150
Work sponsored by SGI
- Ported to kernel 2.3.34
===============================================================================
Changes for patch v151
Work sponsored by SGI
- Ported to kernel 2.3.35-pre1
- Created <devfs_get_name>
===============================================================================
Changes for patch v152
Work sponsored by SGI
- Updated sample modules.conf
- Ported to kernel 2.3.36-pre1
===============================================================================
Changes for patch v153
Work sponsored by SGI
- Ported to kernel 2.3.42
- Removed <devfs_fill_file>
===============================================================================
Changes for patch v154
Work sponsored by SGI
- Took account of device number changes for /dev/fb*
===============================================================================
Changes for patch v155
Work sponsored by SGI
- Ported to kernel 2.3.43-pre8
- Moved /dev/tty0 to /dev/vc/0
- Moved sequence number formatting from <_tty_make_name> to drivers
===============================================================================
Changes for patch v156
Work sponsored by SGI
- Fixed breakage in drivers/scsi/sd.c due to recent SCSI changes
===============================================================================
Changes for patch v157
Work sponsored by SGI
- Ported to kernel 2.3.45
===============================================================================
Changes for patch v158
Work sponsored by SGI
- Ported to kernel 2.3.46-pre2
===============================================================================
Changes for patch v159
Work sponsored by SGI
- Fixed drivers/block/md.c
Thanks to Mike Galbraith <mikeg@weiden.de>
- Documentation fixes
- Moved device registration from <lp_init> to <lp_register>
Thanks to Tim Waugh <twaugh@redhat.com>
===============================================================================
Changes for patch v160
Work sponsored by SGI
- Fixed drivers/char/joystick/joystick.c
Thanks to Vojtech Pavlik <vojtech@suse.cz>
- Documentation updates
- Fixed arch/i386/kernel/mtrr.c if procfs and devfs not enabled
- Fixed drivers/char/stallion.c
===============================================================================
Changes for patch v161
Work sponsored by SGI
- Remove /dev/ide when ide-mod is unloaded
- Fixed bug in drivers/block/ide-probe.c when secondary but no primary
- Added DEVFS_FL_NO_PERSISTENCE flag
- Used new DEVFS_FL_NO_PERSISTENCE flag for Unix98 pty slaves
- Removed unnecessary call to <update_devfs_inode_from_entry> in
<devfs_readdir>
- Only set auto-ownership for /dev/pty/s*
===============================================================================
Changes for patch v162
Work sponsored by SGI
- Set inode->i_size to correct size for symlinks
Thanks to Jeremy Fitzhardinge <jeremy@goop.org>
- Only give lookup() method to directories to comply with new VFS
assumptions
- Remove unnecessary tests in symlink methods
- Don't kill existing block ops in <devfs_read_inode>
- Restore auto-ownership for /dev/pty/m*
===============================================================================
Changes for patch v163
Work sponsored by SGI
- Don't create missing directories in <devfs_find_handle>
- Removed Documentation/filesystems/devfs/mk-devlinks
- Updated Documentation/filesystems/devfs/README
===============================================================================
Changes for patch v164
Work sponsored by SGI
- Fixed CONFIG_DEVFS breakage in drivers/char/serial.c introduced in
linux-2.3.99-pre6-7
===============================================================================
Changes for patch v165
Work sponsored by SGI
- Ported to kernel 2.3.99-pre6
===============================================================================
Changes for patch v166
Work sponsored by SGI
- Added CONFIG_DEVFS_MOUNT
===============================================================================
Changes for patch v167
Work sponsored by SGI
- Updated Documentation/filesystems/devfs/README
- Updated sample modules.conf
===============================================================================
Changes for patch v168
Work sponsored by SGI
- Disabled multi-mount capability (use VFS bindings instead)
- Updated README from master HTML file
===============================================================================
Changes for patch v169
Work sponsored by SGI
- Removed multi-mount code
- Removed compatibility macros: VFS has changed too much
===============================================================================
Changes for patch v170
Work sponsored by SGI
- Updated README from master HTML file
- Merged devfs inode into devfs entry
===============================================================================
Changes for patch v171
Work sponsored by SGI
- Updated sample modules.conf
- Removed dead code in <devfs_register> which used to call
<free_dentries>
- Ported to kernel 2.4.0-test2-pre3
===============================================================================
Changes for patch v172
Work sponsored by SGI
- Changed interface to <devfs_register>
- Changed interface to <devfs_register_series>
===============================================================================
Changes for patch v173
Work sponsored by SGI
- Simplified interface to <devfs_mk_symlink>
- Simplified interface to <devfs_mk_dir>
- Simplified interface to <devfs_find_handle>
===============================================================================
Changes for patch v174
Work sponsored by SGI
- Updated README from master HTML file
===============================================================================
Changes for patch v175
Work sponsored by SGI
- DocBook update for fs/devfs/base.c
Thanks to Tim Waugh <twaugh@redhat.com>
- Removed stale fs/tunnel.c (was never used or completed)
===============================================================================
Changes for patch v176
Work sponsored by SGI
- Updated ToDo list
- Removed sample modules.conf: now distributed with devfsd
- Updated README from master HTML file
- Ported to kernel 2.4.0-test3-pre4 (which had devfs-patch-v174)
===============================================================================
Changes for patch v177
- Updated README from master HTML file
- Documentation cleanups
- Ensure <devfs_generate_path> terminates string for root entry
Thanks to Tim Jansen <tim@tjansen.de>
- Exported <devfs_get_name> to modules
- Make <devfs_mk_symlink> send events to devfsd
- Cleaned up option processing in <devfs_setup>
- Fixed bugs in handling symlinks: could leak or cause Oops
- Cleaned up directory handling by separating fops
Thanks to Alexander Viro <viro@parcelfarce.linux.theplanet.co.uk>
===============================================================================
Changes for patch v178
- Fixed handling of inverted options in <devfs_setup>
===============================================================================
Changes for patch v179
- Adjusted <try_modload> to account for <devfs_generate_path> fix
===============================================================================
Changes for patch v180
- Fixed !CONFIG_DEVFS_FS stub declaration of <devfs_get_info>
===============================================================================
Changes for patch v181
- Answered question posed by Al Viro and removed his comments from <devfs_open>
- Moved setting of registered flag after other fields are changed
- Fixed race between <devfsd_close> and <devfsd_notify_one>
- Global VFS changes added bogus BKL to devfsd_close(): removed
- Widened locking in <devfs_readlink> and <devfs_follow_link>
- Replaced <devfsd_read> stack usage with <devfsd_ioctl> kmalloc
- Simplified locking in <devfsd_ioctl> and fixed memory leak
===============================================================================
Changes for patch v182
- Created <devfs_*alloc_major> and <devfs_*alloc_devnum>
- Removed broken devnum allocation and use <devfs_alloc_devnum>
- Fixed old devnum leak by calling new <devfs_dealloc_devnum>
- Created <devfs_*alloc_unique_number>
- Fixed number leak for /dev/cdroms/cdrom%d
- Fixed number leak for /dev/discs/disc%d
===============================================================================
Changes for patch v183
- Fixed bug in <devfs_setup> which could hang boot process
===============================================================================
Changes for patch v184
- Documentation typo fix for fs/devfs/util.c
- Fixed drivers/char/stallion.c for devfs
- Added DEVFSD_NOTIFY_DELETE event
- Updated README from master HTML file
- Removed #include <asm/segment.h> from fs/devfs/base.c
===============================================================================
Changes for patch v185
- Made <block_semaphore> and <char_semaphore> in fs/devfs/util.c
private
- Fixed inode table races by removing it and using inode->u.generic_ip
instead
- Moved <devfs_read_inode> into <get_vfs_inode>
- Moved <devfs_write_inode> into <devfs_notify_change>
===============================================================================
Changes for patch v186
- Fixed race in <devfs_do_symlink> for uni-processor
- Updated README from master HTML file
===============================================================================
Changes for patch v187
- Fixed drivers/char/stallion.c for devfs
- Fixed drivers/char/rocket.c for devfs
- Fixed bug in <devfs_alloc_unique_number>: limited to 128 numbers
===============================================================================
Changes for patch v188
- Updated major masks in fs/devfs/util.c up to Linus' "no new majors"
proclamation. Block: were 126 now 122 free, char: were 26 now 19 free
- Updated README from master HTML file
- Removed remnant of multi-mount support in <devfs_mknod>
- Removed unused DEVFS_FL_SHOW_UNREG flag
===============================================================================
Changes for patch v189
- Removed nlink field from struct devfs_inode
- Removed auto-ownership for /dev/pty/* (BSD ptys) and used
DEVFS_FL_CURRENT_OWNER|DEVFS_FL_NO_PERSISTENCE for /dev/pty/s* (just
like Unix98 pty slaves) and made /dev/pty/m* rw-rw-rw- access
===============================================================================
Changes for patch v190
- Updated README from master HTML file
- Replaced BKL with global rwsem to protect symlink data (quick and
dirty hack)
===============================================================================
Changes for patch v191
- Replaced global rwsem for symlink with per-link refcount
===============================================================================
Changes for patch v192
- Removed unnecessary #ifdef CONFIG_DEVFS_FS from arch/i386/kernel/mtrr.c
- Ported to kernel 2.4.10-pre11
- Set inode->i_mapping->a_ops for block nodes in <get_vfs_inode>
===============================================================================
Changes for patch v193
- Went back to global rwsem for symlinks (refcount scheme no good)
===============================================================================
Changes for patch v194
- Fixed overrun in <devfs_link> by removing function (not needed)
- Updated README from master HTML file
===============================================================================
Changes for patch v195
- Fixed buffer underrun in <try_modload>
- Moved down_read() from <search_for_entry_in_dir> to <find_entry>
===============================================================================
Changes for patch v196
- Fixed race in <devfsd_ioctl> when setting event mask
Thanks to Kari Hurtta <hurtta@leija.mh.fmi.fi>
- Avoid deadlock in <devfs_follow_link> by using temporary buffer
===============================================================================
Changes for patch v197
- First release of new locking code for devfs core (v1.0)
- Fixed bug in drivers/cdrom/cdrom.c
===============================================================================
Changes for patch v198
- Discard temporary buffer, now use "%s" for dentry names
- Don't generate path in <try_modload>: use fake entry instead
- Use "existing" directory in <_devfs_make_parent_for_leaf>
- Use slab cache rather than fixed buffer for devfsd events
===============================================================================
Changes for patch v199
- Removed obsolete usage of DEVFS_FL_NO_PERSISTENCE
- Send DEVFSD_NOTIFY_REGISTERED events in <devfs_mk_dir>
- Fixed locking bug in <devfs_d_revalidate_wait> due to typo
- Do not send CREATE, CHANGE, ASYNC_OPEN or DELETE events from devfsd
or children
===============================================================================
Changes for patch v200
- Ported to kernel 2.5.1-pre2
===============================================================================
Changes for patch v201
- Fixed bug in <devfsd_read>: was dereferencing freed pointer
===============================================================================
Changes for patch v202
- Fixed bug in <devfsd_close>: was dereferencing freed pointer
- Added process group check for devfsd privileges
===============================================================================
Changes for patch v203
- Use SLAB_ATOMIC in <devfsd_notify_de> from <devfs_d_delete>
===============================================================================
Changes for patch v204
- Removed long obsolete rc.devfs
- Return old entry in <devfs_mk_dir> for 2.4.x kernels
- Updated README from master HTML file
- Increment refcount on module in <check_disc_changed>
- Created <devfs_get_handle> and exported <devfs_put>
- Increment refcount on module in <devfs_get_ops>
- Created <devfs_put_ops> and used where needed to fix races
- Added clarifying comments in response to preliminary EMC code review
- Added poisoning to <devfs_put>
- Improved debugging messages
- Fixed unregister bugs in drivers/md/lvm-fs.c
===============================================================================
Changes for patch v205
- Corrected (made useful) debugging message in <unregister>
- Moved <kmem_cache_create> in <mount_devfs_fs> to <init_devfs_fs>
- Fixed drivers/md/lvm-fs.c to create "lvm" entry
- Added magic number to guard against scribbling drivers
- Only return old entry in <devfs_mk_dir> if a directory
- Defined macros for error and debug messages
- Updated README from master HTML file
===============================================================================
Changes for patch v206
- Added support for multiple Compaq cpqarray controllers
- Fixed (rare, old) race in <devfs_lookup>
===============================================================================
Changes for patch v207
- Fixed deadlock bug in <devfs_d_revalidate_wait>
- Tag VFS deletable in <devfs_mk_symlink> if handle ignored
- Updated README from master HTML file
===============================================================================
Changes for patch v208
- Added KERN_* to remaining messages
- Cleaned up declaration of <stat_read>
- Updated README from master HTML file
===============================================================================
Changes for patch v209
- Updated README from master HTML file
- Removed silently introduced calls to lock_kernel() and
unlock_kernel() due to recent VFS locking changes. BKL isn't
required in devfs
- Changed <devfs_rmdir> to allow later additions if not yet empty
- Added calls to <devfs_register_partitions> in drivers/block/blkpc.c
<add_partition> and <del_partition>
- Fixed bug in <devfs_alloc_unique_number>: was clearing beyond
bitfield
- Fixed bitfield data type for <devfs_*alloc_devnum>
- Made major bitfield type and initialiser 64 bit safe
===============================================================================
Changes for patch v210
- Updated fs/devfs/util.c to fix shift warning on 64 bit machines
Thanks to Anton Blanchard <anton@samba.org>
- Updated README from master HTML file
===============================================================================
Changes for patch v211
- Do not put miscellaneous character devices in /dev/misc if they
specify their own directory (i.e. contain a '/' character)
- Copied macro for error messages from fs/devfs/base.c to
fs/devfs/util.c and made use of this macro
- Removed 2.4.x compatibility code from fs/devfs/base.c
===============================================================================
Changes for patch v212
- Added BKL to <devfs_open> because drivers still need it
===============================================================================
Changes for patch v213
- Protected <scan_dir_for_removable> and <get_removable_partition>
from changing directory contents
===============================================================================
Changes for patch v214
- Switched to ISO C structure field initialisers
- Switch to set_current_state() and move before add_wait_queue()
- Updated README from master HTML file
- Fixed devfs entry leak in <devfs_readdir> when *readdir fails
===============================================================================
Changes for patch v215
- Created <devfs_find_and_unregister>
- Switched many functions from <devfs_find_handle> to
<devfs_find_and_unregister>
- Switched many functions from <devfs_find_handle> to <devfs_get_handle>
===============================================================================
Changes for patch v216
- Switched arch/ia64/sn/io/hcl.c from <devfs_find_handle> to
<devfs_get_handle>
- Removed deprecated <devfs_find_handle>
===============================================================================
Changes for patch v217
- Exported <devfs_find_and_unregister> and <devfs_only> to modules
- Updated README from master HTML file
- Fixed module unload race in <devfs_open>
===============================================================================
Changes for patch v218
- Removed DEVFS_FL_AUTO_OWNER flag
- Switched lingering structure field initialiser to ISO C
- Added locking when setting/clearing flags
- Documentation fix in fs/devfs/util.c
Documentation/filesystems/devfs/README deleted 100644 → 0
View file @ d8deac50
Devfs (Device File System) FAQ
Linux Devfs (Device File System) FAQ
Richard Gooch
20-AUG-2002
Document languages:
-----------------------------------------------------------------------------
NOTE: the master copy of this document is available online at:
http://www.atnf.csiro.au/~rgooch/linux/docs/devfs.html
and looks much better than the text version distributed with the
kernel sources. A mirror site is available at:
http://www.ras.ucalgary.ca/~rgooch/linux/docs/devfs.html
There is also an optional daemon that may be used with devfs. You can
find out more about it at:
http://www.atnf.csiro.au/~rgooch/linux/
A mailing list is available which you may subscribe to. Send
email
to majordomo@oss.sgi.com with the following line in the
body of the message:
subscribe devfs
To unsubscribe, send the message body:
unsubscribe devfs
instead. The list is archived at
http://oss.sgi.com/projects/devfs/archive/.
-----------------------------------------------------------------------------
Contents
What is it?
Why do it?
Who else does it?
How it works
Operational issues (essential reading)
Instructions for the impatient
Permissions persistence across reboots
Dealing with drivers without devfs support
All the way with Devfs
Other Issues
Kernel Naming Scheme
Devfsd Naming Scheme
Old Compatibility Names
SCSI Host Probing Issues
Device drivers currently ported
Allocation of Device Numbers
Questions and Answers
Making things work
Alternatives to devfs
What I don't like about devfs
How to report bugs
Strange kernel messages
Compilation problems with devfsd
Other resources
Translations of this document
-----------------------------------------------------------------------------
What is it?
Devfs is an alternative to "real" character and block special devices
on your root filesystem. Kernel device drivers can register devices by
name rather than major and minor numbers. These devices will appear in
devfs automatically, with whatever default ownership and
protection the driver specified. A daemon (devfsd) can be used to
override these defaults. Devfs has been in the kernel since 2.3.46.
NOTE that devfs is entirely optional. If you prefer the old
disc-based device nodes, then simply leave CONFIG_DEVFS_FS=n (the
default). In this case, nothing will change. ALSO NOTE that if you do
enable devfs, the defaults are such that full compatibility is
maintained with the old devices names.
There are two aspects to devfs: one is the underlying device
namespace, which is a namespace just like any mounted filesystem. The
other aspect is the filesystem code which provides a view of the
device namespace. The reason I make a distinction is because devfs
can be mounted many times, with each mount showing the same device
namespace. Changes made are global to all mounted devfs filesystems.
Also, because the devfs namespace exists without any devfs mounts, you
can easily mount the root filesystem by referring to an entry in the
devfs namespace.
The cost of devfs is a small increase in kernel code size and memory
usage. About 7 pages of code (some of that in __init sections) and 72
bytes for each entry in the namespace. A modest system has only a
couple of hundred device entries, so this costs a few more
pages. Compare this with the suggestion to put /dev on a <a
href="#why-faq-ramdisc">ramdisc.
On a typical machine, the cost is under 0.2 percent. On a modest
system with 64 MBytes of RAM, the cost is under 0.1 percent. The
accusations of "bloatware" levelled at devfs are not justified.
-----------------------------------------------------------------------------
Why do it?
There are several problems that devfs addresses. Some of these
problems are more serious than others (depending on your point of
view), and some can be solved without devfs. However, the totality of
these problems really calls out for devfs.
The choice is a patchwork of inefficient user space solutions, which
are complex and likely to be fragile, or to use a simple and efficient
devfs which is robust.
There have been many counter-proposals to devfs, all seeking to
provide some of the benefits without actually implementing devfs. So
far there has been an absence of code and no proposed alternative has
been able to provide all the features that devfs does. Further,
alternative proposals require far more complexity in user-space (and
still deliver less functionality than devfs). Some people have the
mantra of reducing "kernel bloat", but don't consider the effects on
user-space.
A good solution limits the total complexity of kernel-space and
user-space.
Major&minor allocation
The existing scheme requires the allocation of major and minor device
numbers for each and every device. This means that a central
co-ordinating authority is required to issue these device numbers
(unless you're developing a "private" device driver), in order to
preserve uniqueness. Devfs shifts the burden to a namespace. This may
not seem like a huge benefit, but actually it is. Since driver authors
will naturally choose a device name which reflects the functionality
of the device, there is far less potential for namespace conflict.
Solving this requires a kernel change.
/dev management
Because you currently access devices through device nodes, these must
be created by the system administrator. For standard devices you can
usually find a MAKEDEV programme which creates all these (hundreds!)
of nodes. This means that changes in the kernel must be reflected by
changes in the MAKEDEV programme, or else the system administrator
creates device nodes by hand.
The basic problem is that there are two separate databases of
major and minor numbers. One is in the kernel and one is in /dev (or
in a MAKEDEV programme, if you want to look at it that way). This is
duplication of information, which is not good practice.
Solving this requires a kernel change.
/dev growth
A typical /dev has over 1200 nodes! Most of these devices simply don't
exist because the hardware is not available. A huge /dev increases the
time to access devices (I'm just referring to the dentry lookup times
and the time taken to read inodes off disc: the next subsection shows
some more horrors).
An example of how big /dev can grow is if we consider SCSI devices:
host 6 bits (say up to 64 hosts on a really big machine)
channel 4 bits (say up to 16 SCSI buses per host)
id 4 bits
lun 3 bits
partition 6 bits
TOTAL 23 bits
This requires 8 Mega (1024*1024) inodes if we want to store all
possible device nodes. Even if we scrap everything but id,partition
and assume a single host adapter with a single SCSI bus and only one
logical unit per SCSI target (id), that's still 10 bits or 1024
inodes. Each VFS inode takes around 256 bytes (kernel 2.1.78), so
that's 256 kBytes of inode storage on disc (assuming real inodes take
a similar amount of space as VFS inodes). This is actually not so bad,
because disc is cheap these days. Embedded systems would care about
256 kBytes of /dev inodes, but you could argue that embedded systems
would have hand-tuned /dev directories. I've had to do just that on my
embedded systems, but I would rather just leave it to devfs.
Another issue is the time taken to lookup an inode when first
referenced. Not only does this take time in scanning through a list in
memory, but also the seek times to read the inodes off disc.
This could be solved in user-space using a clever programme which
scanned the kernel logs and deleted /dev entries which are not
available and created them when they were available. This programme
would need to be run every time a new module was loaded, which would
slow things down a lot.
There is an existing programme called scsidev which will automatically
create device nodes for SCSI devices. It can do this by scanning files
in /proc/scsi. Unfortunately, to extend this idea to other device
nodes would require significant modifications to existing drivers (so
they too would provide information in /proc). This is a non-trivial
change (I should know: devfs has had to do something similar). Once
you go to this much effort, you may as well use devfs itself (which
also provides this information). Furthermore, such a system would
likely be implemented in an ad-hoc fashion, as different drivers will
provide their information in different ways.
Devfs is much cleaner, because it (naturally) has a uniform mechanism
to provide this information: the device nodes themselves!
Node to driver file_operations translation
There is an important difference between the way disc-based character
and block nodes and devfs entries make the connection between an entry
in /dev and the actual device driver.
With the current 8 bit major and minor numbers the connection between
disc-based c&b nodes and per-major drivers is done through a
fixed-length table of 128 entries. The various filesystem types set
the inode operations for c&b nodes to {chr,blk}dev_inode_operations,
so when a device is opened a few quick levels of indirection bring us
to the driver file_operations.
For miscellaneous character devices a second step is required: there
is a scan for the driver entry with the same minor number as the file
that was opened, and the appropriate minor open method is called. This
scanning is done *every time* you open a device node. Potentially, you
may be searching through dozens of misc. entries before you find your
open method. While not an enormous performance overhead, this does
seem pointless.
Linux *must* move beyond the 8 bit major and minor barrier,
somehow. If we simply increase each to 16 bits, then the indexing
scheme used for major driver lookup becomes untenable, because the
major tables (one each for character and block devices) would need to
be 64 k entries long (512 kBytes on x86, 1 MByte for 64 bit
systems). So we would have to use a scheme like that used for
miscellaneous character devices, which means the search time goes up
linearly with the average number of major device drivers on your
system. Not all "devices" are hardware, some are higher-level drivers
like KGI, so you can get more "devices" without adding hardware
You can improve this by creating an ordered (balanced:-)
binary tree, in which case your search time becomes log(N).
Alternatively, you can use hashing to speed up the search.
But why do that search at all if you don't have to? Once again, it
seems pointless.
Note that devfs doesn't use the major&minor system. For devfs
entries, the connection is done when you lookup the /dev entry. When
devfs_register() is called, an internal table is appended which has
the entry name and the file_operations. If the dentry cache doesn't
have the /dev entry already, this internal table is scanned to get the
file_operations, and an inode is created. If the dentry cache already
has the entry, there is *no lookup time* (other than the dentry scan
itself, but we can't avoid that anyway, and besides Linux dentries
cream other OS's which don't have them:-). Furthermore, the number of
node entries in a devfs is only the number of available device
entries, not the number of *conceivable* entries. Even if you remove
unnecessary entries in a disc-based /dev, the number of conceivable
entries remains the same: you just limit yourself in order to save
space.
Devfs provides a fast connection between a VFS node and the device
driver, in a scalable way.
/dev as a system administration tool
Right now /dev contains a list of conceivable devices, most of which I
don't have. Devfs only shows those devices available on my
system. This means that listing /dev is a handy way of checking what
devices are available.
Major&minor size
Existing major and minor numbers are limited to 8 bits each. This is
now a limiting factor for some drivers, particularly the SCSI disc
driver, which consumes a single major number. Only 16 discs are
supported, and each disc may have only 15 partitions. Maybe this isn't
a problem for you, but some of us are building huge Linux systems with
disc arrays. With devfs an arbitrary pointer can be associated with
each device entry, which can be used to give an effective 32 bit
device identifier (i.e. that's like having a 32 bit minor
number). Since this is private to the kernel, there are no C library
compatibility issues which you would have with increasing major and
minor number sizes. See the section on "Allocation of Device Numbers"
for details on maintaining compatibility with userspace.
Solving this requires a kernel change.
Since writing this, the kernel has been modified so that the SCSI disc
driver has more major numbers allocated to it and now supports up to
128 discs. Since these major numbers are non-contiguous (a result of
unplanned expansion), the implementation is a little more cumbersome
than originally.
Just like the changes to IPv4 to fix impending limitations in the
address space, people find ways around the limitations. In the long
run, however, solutions like IPv6 or devfs can't be put off forever.
Read-only root filesystem
Having your device nodes on the root filesystem means that you can't
operate properly with a read-only root filesystem. This is because you
want to change ownerships and protections of tty devices. Existing
practice prevents you using a CD-ROM as your root filesystem for a
*real* system. Sure, you can boot off a CD-ROM, but you can't change
tty ownerships, so it's only good for installing.
Also, you can't use a shared NFS root filesystem for a cluster of
discless Linux machines (having tty ownerships changed on a common
/dev is not good). Nor can you embed your root filesystem in a
ROM-FS.
You can get around this by creating a RAMDISC at boot time, making
an ext2 filesystem in it, mounting it somewhere and copying the
contents of /dev into it, then unmounting it and mounting it over
/dev.
A devfs is a cleaner way of solving this.
Non-Unix root filesystem
Non-Unix filesystems (such as NTFS) can't be used for a root
filesystem because they variously don't support character and block
special files or symbolic links. You can't have a separate disc-based
or RAMDISC-based filesystem mounted on /dev because you need device
nodes before you can mount these. Devfs can be mounted without any
device nodes. Devlinks won't work because symlinks aren't supported.
An alternative solution is to use initrd to mount a RAMDISC initial
root filesystem (which is populated with a minimal set of device
nodes), and then construct a new /dev in another RAMDISC, and finally
switch to your non-Unix root filesystem. This requires clever boot
scripts and a fragile and conceptually complex boot procedure.
Devfs solves this in a robust and conceptually simple way.
PTY security
Current pseudo-tty (pty) devices are owned by root and read-writable
by everyone. The user of a pty-pair cannot change
ownership/protections without being suid-root.
This could be solved with a secure user-space daemon which runs as
root and does the actual creation of pty-pairs. Such a daemon would
require modification to *every* programme that wants to use this new
mechanism. It also slows down creation of pty-pairs.
An alternative is to create a new open_pty() syscall which does much
the same thing as the user-space daemon. Once again, this requires
modifications to pty-handling programmes.
The devfs solution allows a device driver to "tag" certain device
files so that when an unopened device is opened, the ownerships are
changed to the current euid and egid of the opening process, and the
protections are changed to the default registered by the driver. When
the device is closed ownership is set back to root and protections are
set back to read-write for everybody. No programme need be changed.
The devpts filesystem provides this auto-ownership feature for Unix98
ptys. It doesn't support old-style pty devices, nor does it have all
the other features of devfs.
Intelligent device management
Devfs implements a simple yet powerful protocol for communication with
a device management daemon (devfsd) which runs in user space. It is
possible to send a message (either synchronously or asynchronously) to
devfsd on any event, such as registration/unregistration of device
entries, opening and closing devices, looking up inodes, scanning
directories and more. This has many possibilities. Some of these are
already implemented. See:
http://www.atnf.csiro.au/~rgooch/linux/
Device entry registration events can be used by devfsd to change
permissions of newly-created device nodes. This is one mechanism to
control device permissions.
Device entry registration/unregistration events can be used to run
programmes or scripts. This can be used to provide automatic mounting
of filesystems when a new block device media is inserted into the
drive.
Asynchronous device open and close events can be used to implement
clever permissions management. For example, the default permissions on
/dev/dsp do not allow everybody to read from the device. This is
sensible, as you don't want some remote user recording what you say at
your console. However, the console user is also prevented from
recording. This behaviour is not desirable. With asynchronous device
open and close events, you can have devfsd run a programme or script
when console devices are opened to change the ownerships for *other*
device nodes (such as /dev/dsp). On closure, you can run a different
script to restore permissions. An advantage of this scheme over
modifying the C library tty handling is that this works even if your
programme crashes (how many times have you seen the utmp database with
lingering entries for non-existent logins?).
Synchronous device open events can be used to perform intelligent
device access protections. Before the device driver open() method is
called, the daemon must first validate the open attempt, by running an
external programme or script. This is far more flexible than access
control lists, as access can be determined on the basis of other
system conditions instead of just the UID and GID.
Inode lookup events can be used to authenticate module autoload
requests. Instead of using kmod directly, the event is sent to
devfsd which can implement an arbitrary authentication before loading
the module itself.
Inode lookup events can also be used to construct arbitrary
namespaces, without having to resort to populating devfs with symlinks
to devices that don't exist.
Speculative Device Scanning
Consider an application (like cdparanoia) that wants to find all
CD-ROM devices on the system (SCSI, IDE and other types), whether or
not their respective modules are loaded. The application must
speculatively open certain device nodes (such as /dev/sr0 for the SCSI
CD-ROMs) in order to make sure the module is loaded. This requires
that all Linux distributions follow the standard device naming scheme
(last time I looked RedHat did things differently). Devfs solves the
naming problem.
The same application also wants to see which devices are actually
available on the system. With the existing system it needs to read the
/dev directory and speculatively open each /dev/sr* device to
determine if the device exists or not. With a large /dev this is an
inefficient operation, especially if there are many /dev/sr* nodes. A
solution like scsidev could reduce the number of /dev/sr* entries (but
of course that also requires all that inefficient directory scanning).
With devfs, the application can open the /dev/sr directory
(which triggers the module autoloading if required), and proceed to
read /dev/sr. Since only the available devices will have
entries, there are no inefficencies in directory scanning or device
openings.
-----------------------------------------------------------------------------
Who else does it?
FreeBSD has a devfs implementation. Solaris and AIX each have a
pseudo-devfs (something akin to scsidev but for all devices, with some
unspecified kernel support). BeOS, Plan9 and QNX also have it. SGI's
IRIX 6.4 and above also have a device filesystem.
While we shouldn't just automatically do something because others do
it, we should not ignore the work of others either. FreeBSD has a lot
of competent people working on it, so their opinion should not be
blithely ignored.
-----------------------------------------------------------------------------
How it works
Registering device entries
For every entry (device node) in a devfs-based /dev a driver must call
devfs_register(). This adds the name of the device entry, the
file_operations structure pointer and a few other things to an
internal table. Device entries may be added and removed at any
time. When a device entry is registered, it automagically appears in
any mounted devfs'.
Inode lookup
When a lookup operation on an entry is performed and if there is no
driver information for that entry devfs will attempt to call
devfsd. If still no driver information can be found then a negative
dentry is yielded and the next stage operation will be called by the
VFS (such as create() or mknod() inode methods). If driver information
can be found, an inode is created (if one does not exist already) and
all is well.
Manually creating device nodes
The mknod() method allows you to create an ordinary named pipe in the
devfs, or you can create a character or block special inode if one
does not already exist. You may wish to create a character or block
special inode so that you can set permissions and ownership. Later, if
a device driver registers an entry with the same name, the
permissions, ownership and times are retained. This is how you can set
the protections on a device even before the driver is loaded. Once you
create an inode it appears in the directory listing.
Unregistering device entries
A device driver calls devfs_unregister() to unregister an entry.
Chroot() gaols
2.2.x kernels
The semantics of inode creation are different when devfs is mounted
with the "explicit" option. Now, when a device entry is registered, it
will not appear until you use mknod() to create the device. It doesn't
matter if you mknod() before or after the device is registered with
devfs_register(). The purpose of this behaviour is to support
chroot(2) gaols, where you want to mount a minimal devfs inside the
gaol. Only the devices you specifically want to be available (through
your mknod() setup) will be accessible.
2.4.x kernels
As of kernel 2.3.99, the VFS has had the ability to rebind parts of
the global filesystem namespace into another part of the namespace.
This now works even at the leaf-node level, which means that
individual files and device nodes may be bound into other parts of the
namespace. This is like making links, but better, because it works
across filesystems (unlike hard links) and works through chroot()
gaols (unlike symbolic links).
Because of these improvements to the VFS, the multi-mount capability
in devfs is no longer needed. The administrator may create a minimal
device tree inside a chroot(2) gaol by using VFS bindings. As this
provides most of the features of the devfs multi-mount capability, I
removed the multi-mount support code (after issuing an RFC). This
yielded code size reductions and simplifications.
If you want to construct a minimal chroot() gaol, the following
command should suffice:
mount --bind /dev/null /gaol/dev/null
Repeat for other device nodes you want to expose. Simple!
-----------------------------------------------------------------------------
Operational issues
Instructions for the impatient
Nobody likes reading documentation. People just want to get in there
and play. So this section tells you quickly the steps you need to take
to run with devfs mounted over /dev. Skip these steps and you will end
up with a nearly unbootable system. Subsequent sections describe the
issues in more detail, and discuss non-essential configuration
options.
Devfsd
OK, if you're reading this, I assume you want to play with
devfs. First you should ensure that /usr/src/linux contains a
recent kernel source tree. Then you need to compile devfsd, the device
management daemon, available at
http://www.atnf.csiro.au/~rgooch/linux/.
Because the kernel has a naming scheme
which is quite different from the old naming scheme, you need to
install devfsd so that software and configuration files that use the
old naming scheme will not break.
Compile and install devfsd. You will be provided with a default
configuration file /etc/devfsd.conf which will provide
compatibility symlinks for the old naming scheme. Don't change this
config file unless you know what you're doing. Even if you think you
do know what you're doing, don't change it until you've followed all
the steps below and booted a devfs-enabled system and verified that it
works.
Now edit your main system boot script so that devfsd is started at the
very beginning (before any filesystem
checks). /etc/rc.d/rc.sysinit is often the main boot script
on systems with SysV-style boot scripts. On systems with BSD-style
boot scripts it is often /etc/rc. Also check
/sbin/rc.
NOTE that the line you put into the boot
script should be exactly:
/sbin/devfsd /dev
DO NOT use some special daemon-launching
programme, otherwise the boot script may not wait for devfsd to finish
initialising.
System Libraries
There may still be some problems because of broken software making
assumptions about device names. In particular, some software does not
handle devices which are symbolic links. If you are running a libc 5
based system, install libc 5.4.44 (if you have libc 5.4.46, go back to
libc 5.4.44, which is actually correct). If you are running a glibc
based system, make sure you have glibc 2.1.3 or later.
/etc/securetty
PAM (Pluggable Authentication Modules) is supposed to be a flexible
mechanism for providing better user authentication and access to
services. Unfortunately, it's also fragile, complex and undocumented
(check out RedHat 6.1, and probably other distributions as well). PAM
has problems with symbolic links. Append the following lines to your
/etc/securetty file:
vc/1
vc/2
vc/3
vc/4
vc/5
vc/6
vc/7
vc/8
This will not weaken security. If you have a version of util-linux
earlier than 2.10.h, please upgrade to 2.10.h or later. If you
absolutely cannot upgrade, then also append the following lines to
your /etc/securetty file:
1
2
3
4
5
6
7
8
This may potentially weaken security by allowing root logins over the
network (a password is still required, though). However, since there
are problems with dealing with symlinks, I'm suspicious of the level
of security offered in any case.
XFree86
While not essential, it's probably a good idea to upgrade to XFree86
4.0, as patches went in to make it more devfs-friendly. If you don't,
you'll probably need to apply the following patch to
/etc/security/console.perms so that ordinary users can run
startx. Note that not all distributions have this file (e.g. Debian),
so if it's not present, don't worry about it.
--- /etc/security/console.perms.orig Sat Apr 17 16:26:47 1999
+++ /etc/security/console.perms Fri Feb 25 23:53:55 2000
@@ -14,7 +14,7 @@
# man 5 console.perms
# file classes -- these are regular expressions
-<console>=tty[0-9][0-9]* :[0-9]\.[0-9] :[0-9]
+<console>=tty[0-9][0-9]* vc/[0-9][0-9]* :[0-9]\.[0-9] :[0-9]
# device classes -- these are shell-style globs
<floppy>=/dev/fd[0-1]*
If the patch does not apply, then change the line:
<console>=tty[0-9][0-9]* :[0-9]\.[0-9] :[0-9]
with:
<console>=tty[0-9][0-9]* vc/[0-9][0-9]* :[0-9]\.[0-9] :[0-9]
Disable devpts
I've had a report of devpts mounted on /dev/pts not working
correctly. Since devfs will also manage /dev/pts, there is no
need to mount devpts as well. You should either edit your
/etc/fstab so devpts is not mounted, or disable devpts from
your kernel configuration.
Unsupported drivers
Not all drivers have devfs support. If you depend on one of these
drivers, you will need to create a script or tarfile that you can use
at boot time to create device nodes as appropriate. There is a
section which describes this. Another
section lists the drivers which have
devfs support.
/dev/mouse
Many disributions configure /dev/mouse to be the mouse device
for XFree86 and GPM. I actually think this is a bad idea, because it
adds another level of indirection. When looking at a config file, if
you see /dev/mouse you're left wondering which mouse
is being referred to. Hence I recommend putting the actual mouse
device (for example /dev/psaux) into your
/etc/X11/XF86Config file (and similarly for the GPM
configuration file).
Alternatively, use the same technique used for unsupported drivers
described above.
The Kernel
Finally, you need to make sure devfs is compiled into your kernel. Set
CONFIG_EXPERIMENTAL=y, CONFIG_DEVFS_FS=y and CONFIG_DEVFS_MOUNT=y by
using favourite configuration tool (i.e. make config or
make xconfig) and then make clean and then recompile your kernel and
modules. At boot, devfs will be mounted onto /dev.
If you encounter problems booting (for example if you forgot a
configuration step), you can pass devfs=nomount at the kernel
boot command line. This will prevent the kernel from mounting devfs at
boot time onto /dev.
In general, a kernel built with CONFIG_DEVFS_FS=y but without mounting
devfs onto /dev is completely safe, and requires no
configuration changes. One exception to take note of is when
LABEL= directives are used in /etc/fstab. In this
case you will be unable to boot properly. This is because the
mount(8) programme uses /proc/partitions as part of
the volume label search process, and the device names it finds are not
available, because setting CONFIG_DEVFS_FS=y changes the names in
/proc/partitions, irrespective of whether devfs is mounted.
Now you've finished all the steps required. You're now ready to boot
your shiny new kernel. Enjoy.
Changing the configuration
OK, you've now booted a devfs-enabled system, and everything works.
Now you may feel like changing the configuration (common targets are
/etc/fstab and /etc/devfsd.conf). Since you have a
system that works, if you make any changes and it doesn't work, you
now know that you only have to restore your configuration files to the
default and it will work again.
Permissions persistence across reboots
If you don't use mknod(2) to create a device file, nor use chmod(2) or
chown(2) to change the ownerships/permissions, the inode ctime will
remain at 0 (the epoch, 12 am, 1-JAN-1970, GMT). Anything with a ctime
later than this has had it's ownership/permissions changed. Hence, a
simple script or programme may be used to tar up all changed inodes,
prior to shutdown. Although effective, many consider this approach a
kludge.
A much better approach is to use devfsd to save and restore
permissions. It may be configured to record changes in permissions and
will save them in a database (in fact a directory tree), and restore
these upon boot. This is an efficient method and results in immediate
saving of current permissions (unlike the tar approach, which saves
permissions at some unspecified future time).
The default configuration file supplied with devfsd has config entries
which you may uncomment to enable persistence management.
If you decide to use the tar approach anyway, be aware that tar will
first unlink(2) an inode before creating a new device node. The
unlink(2) has the effect of breaking the connection between a devfs
entry and the device driver. If you use the "devfs=only" boot option,
you lose access to the device driver, requiring you to reload the
module. I consider this a bug in tar (there is no real need to
unlink(2) the inode first).
Alternatively, you can use devfsd to provide more sophisticated
management of device permissions. You can use devfsd to store
permissions for whole groups of devices with a single configuration
entry, rather than the conventional single entry per device entry.
Permissions database stored in mounted-over /dev
If you wish to save and restore your device permissions into the
disc-based /dev while still mounting devfs onto /dev
you may do so. This requires a 2.4.x kernel (in fact, 2.3.99 or
later), which has the VFS binding facility. You need to do the
following to set this up:
make sure the kernel does not mount devfs at boot time
make sure you have a correct /dev/console entry in your
root file-system (where your disc-based /dev lives)
create the /dev-state directory
add the following lines near the very beginning of your boot
scripts:
mount --bind /dev /dev-state
mount -t devfs none /dev
devfsd /dev
add the following lines to your /etc/devfsd.conf file:
REGISTER ^pt[sy] IGNORE
CREATE ^pt[sy] IGNORE
CHANGE ^pt[sy] IGNORE
DELETE ^pt[sy] IGNORE
REGISTER .* COPY /dev-state/$devname $devpath
CREATE .* COPY $devpath /dev-state/$devname
CHANGE .* COPY $devpath /dev-state/$devname
DELETE .* CFUNCTION GLOBAL unlink /dev-state/$devname
RESTORE /dev-state
Note that the sample devfsd.conf file contains these lines,
as well as other sample configurations you may find useful. See the
devfsd distribution
reboot.
Permissions database stored in normal directory
If you are using an older kernel which doesn't support VFS binding,
then you won't be able to have the permissions database in a
mounted-over /dev. However, you can still use a regular
directory to store the database. The sample /etc/devfsd.conf
file above may still be used. You will need to create the
/dev-state directory prior to installing devfsd. If you have
old permissions in /dev, then just copy (or move) the device
nodes over to the new directory.
Which method is better?
The best method is to have the permissions database stored in the
mounted-over /dev. This is because you will not need to copy
device nodes over to /dev-state, and because it allows you to
switch between devfs and non-devfs kernels, without requiring you to
copy permissions between /dev-state (for devfs) and
/dev (for non-devfs).
Dealing with drivers without devfs support
Currently, not all device drivers in the kernel have been modified to
use devfs. Device drivers which do not yet have devfs support will not
automagically appear in devfs. The simplest way to create device nodes
for these drivers is to unpack a tarfile containing the required
device nodes. You can do this in your boot scripts. All your drivers
will now work as before.
Hopefully for most people devfs will have enough support so that they
can mount devfs directly over /dev without losing most functionality
(i.e. losing access to various devices). As of 22-JAN-1998 (devfs
patch version 10) I am now running this way. All the devices I have
are available in devfs, so I don't lose anything.
WARNING: if your configuration requires the old-style device names
(i.e. /dev/hda1 or /dev/sda1), you must install devfsd and configure
it to maintain compatibility entries. It is almost certain that you
will require this. Note that the kernel creates a compatibility entry
for the root device, so you don't need initrd.
Note that you no longer need to mount devpts if you use Unix98 PTYs,
as devfs can manage /dev/pts itself. This saves you some RAM, as you
don't need to compile and install devpts. Note that some versions of
glibc have a bug with Unix98 pty handling on devfs systems. Contact
the glibc maintainers for a fix. Glibc 2.1.3 has the fix.
Note also that apart from editing /etc/fstab, other things will need
to be changed if you *don't* install devfsd. Some software (like the X
server) hard-wire device names in their source. It really is much
easier to install devfsd so that compatibility entries are created.
You can then slowly migrate your system to using the new device names
(for example, by starting with /etc/fstab), and then limiting the
compatibility entries that devfsd creates.
IF YOU CONFIGURE TO MOUNT DEVFS AT BOOT, MAKE SURE YOU INSTALL DEVFSD
BEFORE YOU BOOT A DEVFS-ENABLED KERNEL!
Now that devfs has gone into the 2.3.46 kernel, I'm getting a lot of
reports back. Many of these are because people are trying to run
without devfsd, and hence some things break. Please just run devfsd if
things break. I want to concentrate on real bugs rather than
misconfiguration problems at the moment. If people are willing to fix
bugs/false assumptions in other code (i.e. glibc, X server) and submit
that to the respective maintainers, that would be great.
All the way with Devfs
The devfs kernel patch creates a rationalised device tree. As stated
above, if you want to keep using the old /dev naming scheme,
you just need to configure devfsd appopriately (see the man
page). People who prefer the old names can ignore this section. For
those of us who like the rationalised names and an uncluttered
/dev, read on.
If you don't run devfsd, or don't enable compatibility entry
management, then you will have to configure your system to use the new
names. For example, you will then need to edit your
/etc/fstab to use the new disc naming scheme. If you want to
be able to boot non-devfs kernels, you will need compatibility
symlinks in the underlying disc-based /dev pointing back to
the old-style names for when you boot a kernel without devfs.
You can selectively decide which devices you want compatibility
entries for. For example, you may only want compatibility entries for
BSD pseudo-terminal devices (otherwise you'll have to patch you C
library or use Unix98 ptys instead). It's just a matter of putting in
the correct regular expression into /dev/devfsd.conf.
There are other choices of naming schemes that you may prefer. For
example, I don't use the kernel-supplied
names, because they are too verbose. A common misconception is
that the kernel-supplied names are meant to be used directly in
configuration files. This is not the case. They are designed to
reflect the layout of the devices attached and to provide easy
classification.
If you like the kernel-supplied names, that's fine. If you don't then
you should be using devfsd to construct a namespace more to your
liking. Devfsd has built-in code to construct a
namespace that is both logical and easy to
manage. In essence, it creates a convenient abbreviation of the
kernel-supplied namespace.
You are of course free to build your own namespace. Devfsd has all the
infrastructure required to make this easy for you. All you need do is
write a script. You can even write some C code and devfsd can load the
shared object as a callable extension.
Other Issues
The init programme
Another thing to take note of is whether your init programme
creates a Unix socket /dev/telinit. Some versions of init
create /dev/telinit so that the telinit programme can
communicate with the init process. If you have such a system you need
to make sure that devfs is mounted over /dev *before* init
starts. In other words, you can't leave the mounting of devfs to
/etc/rc, since this is executed after init. Other
versions of init require a named pipe /dev/initctl
which must exist *before* init starts. Once again, you need to
mount devfs and then create the named pipe *before* init
starts.
The default behaviour now is not to mount devfs onto /dev at
boot time for 2.3.x and later kernels. You can correct this with the
"devfs=mount" boot option. This solves any problems with init,
and also prevents the dreaded:
Cannot open initial console
message. For 2.2.x kernels where you need to apply the devfs patch,
the default is to mount.
If you have automatic mounting of devfs onto /dev then you
may need to create /dev/initctl in your boot scripts. The
following lines should suffice:
mknod /dev/initctl p
kill -SIGUSR1 1 # tell init that /dev/initctl now exists
Alternatively, if you don't want the kernel to mount devfs onto
/dev then you could use the following procedure is a
guideline for how to get around /dev/initctl problems:
# cd /sbin
# mv init init.real
# cat > init
#! /bin/sh
mount -n -t devfs none /dev
mknod /dev/initctl p
exec /sbin/init.real $*
[control-D]
# chmod a+x init
Note that newer versions of init create /dev/initctl
automatically, so you don't have to worry about this.
Module autoloading
You will need to configure devfsd to enable module
autoloading. The following lines should be placed in your
/etc/devfsd.conf file:
LOOKUP .* MODLOAD
As of devfsd-v1.3.10, a generic /etc/modules.devfs
configuration file is installed, which is used by the MODLOAD
action. This should be sufficient for most configurations. If you
require further configuration, edit your /etc/modules.conf
file. The way module autoloading work with devfs is:
a process attempts to lookup a device node (e.g. /dev/fred)
if that device node does not exist, the full pathname is passed to
devfsd as a string
devfsd will pass the string to the modprobe programme (provided the
configuration line shown above is present), and specifies that
/etc/modules.devfs is the configuration file
/etc/modules.devfs includes /etc/modules.conf to
access local configurations
modprobe will search it's configuration files, looking for an alias
that translates the pathname into a module name
the translated pathname is then used to load the module.
If you wanted a lookup of /dev/fred to load the
mymod module, you would require the following configuration
line in /etc/modules.conf:
alias /dev/fred mymod
The /etc/modules.devfs configuration file provides many such
aliases for standard device names. If you look closely at this file,
you will note that some modules require multiple alias configuration
lines. This is required to support module autoloading for old and new
device names.
Mounting root off a devfs device
If you wish to mount root off a devfs device when you pass the
"devfs=only" boot option, then you need to pass in the
"root=<device>" option to the kernel when booting. If you use
LILO, then you must have this in lilo.conf:
append = "root=<device>"
Surprised? Yep, so was I. It turns out if you have (as most people
do):
root = <device>
then LILO will determine the device number of <device> and will
write that device number into a special place in the kernel image
before starting the kernel, and the kernel will use that device number
to mount the root filesystem. So, using the "append" variety ensures
that LILO passes the root filesystem device as a string, which devfs
can then use.
Note that this isn't an issue if you don't pass "devfs=only".
TTY issues
The ttyname(3) function in some versions of the C library makes
false assumptions about device entries which are symbolic links. The
tty(1) programme is one that depends on this function. I've
written a patch to libc 5.4.43 which fixes this. This has been
included in libc 5.4.44 and a similar fix is in glibc 2.1.3.
Kernel Naming Scheme
The kernel provides a default naming scheme. This scheme is designed
to make it easy to search for specific devices or device types, and to
view the available devices. Some device types (such as hard discs),
have a directory of entries, making it easy to see what devices of
that class are available. Often, the entries are symbolic links into a
directory tree that reflects the topology of available devices. The
topological tree is useful for finding how your devices are arranged.
Below is a list of the naming schemes for the most common drivers. A
list of reserved device names is
available for reference. Please send email to
rgooch@atnf.csiro.au to obtain an allocation. Please be
patient (the maintainer is busy). An alternative name may be allocated
instead of the requested name, at the discretion of the maintainer.
Disc Devices
All discs, whether SCSI, IDE or whatever, are placed under the
/dev/discs hierarchy:
/dev/discs/disc0 first disc
/dev/discs/disc1 second disc
Each of these entries is a symbolic link to the directory for that
device. The device directory contains:
disc for the whole disc
part* for individual partitions
CD-ROM Devices
All CD-ROMs, whether SCSI, IDE or whatever, are placed under the
/dev/cdroms hierarchy:
/dev/cdroms/cdrom0 first CD-ROM
/dev/cdroms/cdrom1 second CD-ROM
Each of these entries is a symbolic link to the real device entry for
that device.
Tape Devices
All tapes, whether SCSI, IDE or whatever, are placed under the
/dev/tapes hierarchy:
/dev/tapes/tape0 first tape
/dev/tapes/tape1 second tape
Each of these entries is a symbolic link to the directory for that
device. The device directory contains:
mt for mode 0
mtl for mode 1
mtm for mode 2
mta for mode 3
mtn for mode 0, no rewind
mtln for mode 1, no rewind
mtmn for mode 2, no rewind
mtan for mode 3, no rewind
SCSI Devices
To uniquely identify any SCSI device requires the following
information:
controller (host adapter)
bus (SCSI channel)
target (SCSI ID)
unit (Logical Unit Number)
All SCSI devices are placed under /dev/scsi (assuming devfs
is mounted on /dev). Hence, a SCSI device with the following
parameters: c=1,b=2,t=3,u=4 would appear as:
/dev/scsi/host1/bus2/target3/lun4 device directory
Inside this directory, a number of device entries may be created,
depending on which SCSI device-type drivers were installed.
See the section on the disc naming scheme to see what entries the SCSI
disc driver creates.
See the section on the tape naming scheme to see what entries the SCSI
tape driver creates.
The SCSI CD-ROM driver creates:
cd
The SCSI generic driver creates:
generic
IDE Devices
To uniquely identify any IDE device requires the following
information:
controller
bus (aka. primary/secondary)
target (aka. master/slave)
unit
All IDE devices are placed under /dev/ide, and uses a similar
naming scheme to the SCSI subsystem.
XT Hard Discs
All XT discs are placed under /dev/xd. The first XT disc has
the directory /dev/xd/disc0.
TTY devices
The tty devices now appear as:
New name Old-name Device Type
-------- -------- -----------
/dev/tts/{0,1,...} /dev/ttyS{0,1,...} Serial ports
/dev/cua/{0,1,...} /dev/cua{0,1,...} Call out devices
/dev/vc/0 /dev/tty Current virtual console
/dev/vc/{1,2,...} /dev/tty{1...63} Virtual consoles
/dev/vcc/{0,1,...} /dev/vcs{1...63} Virtual consoles
/dev/pty/m{0,1,...} /dev/ptyp?? PTY masters
/dev/pty/s{0,1,...} /dev/ttyp?? PTY slaves
RAMDISCS
The RAMDISCS are placed in their own directory, and are named thus:
/dev/rd/{0,1,2,...}
Meta Devices
The meta devices are placed in their own directory, and are named
thus:
/dev/md/{0,1,2,...}
Floppy discs
Floppy discs are placed in the /dev/floppy directory.
Loop devices
Loop devices are placed in the /dev/loop directory.
Sound devices
Sound devices are placed in the /dev/sound directory
(audio, sequencer, ...).
Devfsd Naming Scheme
Devfsd provides a naming scheme which is a convenient abbreviation of
the kernel-supplied namespace. In some
cases, the kernel-supplied naming scheme is quite convenient, so
devfsd does not provide another naming scheme. The convenience names
that devfsd creates are in fact the same names as the original devfs
kernel patch created (before Linus mandated the Big Name
Change). These are referred to as "new compatibility entries".
In order to configure devfsd to create these convenience names, the
following lines should be placed in your /etc/devfsd.conf:
REGISTER .* MKNEWCOMPAT
UNREGISTER .* RMNEWCOMPAT
This will cause devfsd to create (and destroy) symbolic links which
point to the kernel-supplied names.
SCSI Hard Discs
All SCSI discs are placed under /dev/sd (assuming devfs is
mounted on /dev). Hence, a SCSI disc with the following
parameters: c=1,b=2,t=3,u=4 would appear as:
/dev/sd/c1b2t3u4 for the whole disc
/dev/sd/c1b2t3u4p5 for the 5th partition
/dev/sd/c1b2t3u4p5s6 for the 6th slice in the 5th partition
SCSI Tapes
All SCSI tapes are placed under /dev/st. A similar naming
scheme is used as for SCSI discs. A SCSI tape with the
parameters:c=1,b=2,t=3,u=4 would appear as:
/dev/st/c1b2t3u4m0 for mode 0
/dev/st/c1b2t3u4m1 for mode 1
/dev/st/c1b2t3u4m2 for mode 2
/dev/st/c1b2t3u4m3 for mode 3
/dev/st/c1b2t3u4m0n for mode 0, no rewind
/dev/st/c1b2t3u4m1n for mode 1, no rewind
/dev/st/c1b2t3u4m2n for mode 2, no rewind
/dev/st/c1b2t3u4m3n for mode 3, no rewind
SCSI CD-ROMs
All SCSI CD-ROMs are placed under /dev/sr. A similar naming
scheme is used as for SCSI discs. A SCSI CD-ROM with the
parameters:c=1,b=2,t=3,u=4 would appear as:
/dev/sr/c1b2t3u4
SCSI Generic Devices
The generic (aka. raw) interface for all SCSI devices are placed under
/dev/sg. A similar naming scheme is used as for SCSI discs. A
SCSI generic device with the parameters:c=1,b=2,t=3,u=4 would appear
as:
/dev/sg/c1b2t3u4
IDE Hard Discs
All IDE discs are placed under /dev/ide/hd, using a similar
convention to SCSI discs. The following mappings exist between the new
and the old names:
/dev/hda /dev/ide/hd/c0b0t0u0
/dev/hdb /dev/ide/hd/c0b0t1u0
/dev/hdc /dev/ide/hd/c0b1t0u0
/dev/hdd /dev/ide/hd/c0b1t1u0
IDE Tapes
A similar naming scheme is used as for IDE discs. The entries will
appear in the /dev/ide/mt directory.
IDE CD-ROM
A similar naming scheme is used as for IDE discs. The entries will
appear in the /dev/ide/cd directory.
IDE Floppies
A similar naming scheme is used as for IDE discs. The entries will
appear in the /dev/ide/fd directory.
XT Hard Discs
All XT discs are placed under /dev/xd. The first XT disc
would appear as /dev/xd/c0t0.
Old Compatibility Names
The old compatibility names are the legacy device names, such as
/dev/hda, /dev/sda, /dev/rtc and so on.
Devfsd can be configured to create compatibility symlinks so that you
may continue to use the old names in your configuration files and so
that old applications will continue to function correctly.
In order to configure devfsd to create these legacy names, the
following lines should be placed in your /etc/devfsd.conf:
REGISTER .* MKOLDCOMPAT
UNREGISTER .* RMOLDCOMPAT
This will cause devfsd to create (and destroy) symbolic links which
point to the kernel-supplied names.
-----------------------------------------------------------------------------
Device drivers currently ported
- All miscellaneous character devices support devfs (this is done
transparently through misc_register())
- SCSI discs and generic hard discs
- Character memory devices (null, zero, full and so on)
Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
- Loop devices (/dev/loop?)
- TTY devices (console, serial ports, terminals and pseudo-terminals)
Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
- SCSI tapes (/dev/scsi and /dev/tapes)
- SCSI CD-ROMs (/dev/scsi and /dev/cdroms)
- SCSI generic devices (/dev/scsi)
- RAMDISCS (/dev/ram?)
- Meta Devices (/dev/md*)
- Floppy discs (/dev/floppy)
- Parallel port printers (/dev/printers)
- Sound devices (/dev/sound)
Thanks to Eric Dumas <dumas@linux.eu.org> and
C. Scott Ananian <cananian@alumni.princeton.edu>
- Joysticks (/dev/joysticks)
- Sparc keyboard (/dev/kbd)
- DSP56001 digital signal processor (/dev/dsp56k)
- Apple Desktop Bus (/dev/adb)
- Coda network file system (/dev/cfs*)
- Virtual console capture devices (/dev/vcc)
Thanks to Dennis Hou <smilax@mindmeld.yi.org>
- Frame buffer devices (/dev/fb)
- Video capture devices (/dev/v4l)
-----------------------------------------------------------------------------
Allocation of Device Numbers
Devfs allows you to write a driver which doesn't need to allocate a
device number (major&minor numbers) for the internal operation of the
kernel. However, there are a number of userspace programmes that use
the device number as a unique handle for a device. An example is the
find programme, which uses device numbers to determine whether
an inode is on a different filesystem than another inode. The device
number used is the one for the block device which a filesystem is
using. To preserve compatibility with userspace programmes, block
devices using devfs need to have unique device numbers allocated to
them. Furthermore, POSIX specifies device numbers, so some kind of
device number needs to be presented to userspace.
The simplest option (especially when porting drivers to devfs) is to
keep using the old major and minor numbers. Devfs will take whatever
values are given for major&minor and pass them onto userspace.
This device number is a 16 bit number, so this leaves plenty of space
for large numbers of discs and partitions. This scheme can also be
used for character devices, in particular the tty devices, which are
currently limited to 256 pseudo-ttys (this limits the total number of
simultaneous xterms and remote logins). Note that the device number
is limited to the range 36864-61439 (majors 144-239), in order to
avoid any possible conflicts with existing official allocations.
Please note that using dynamically allocated block device numbers may
break the NFS daemons (both user and kernel mode), which expect dev_t
for a given device to be constant over the lifetime of remote mounts.
A final note on this scheme: since it doesn't increase the size of
device numbers, there are no compatibility issues with userspace.
-----------------------------------------------------------------------------
Questions and Answers
Making things work
Alternatives to devfs
What I don't like about devfs
How to report bugs
Strange kernel messages
Compilation problems with devfsd
Making things work
Here are some common questions and answers.
Devfsd doesn't start
Make sure you have compiled and installed devfsd
Make sure devfsd is being started from your boot
scripts
Make sure you have configured your kernel to enable devfs (see
below)
Make sure devfs is mounted (see below)
Devfsd is not managing all my permissions
Make sure you are capturing the appropriate events. For example,
device entries created by the kernel generate REGISTER events,
but those created by devfsd generate CREATE events.
Devfsd is not capturing all REGISTER events
See the previous entry: you may need to capture CREATE events.
X will not start
Make sure you followed the steps
outlined above.
Why don't my network devices appear in devfs?
This is not a bug. Network devices have their own, completely separate
namespace. They are accessed via socket(2) and
setsockopt(2) calls, and thus require no device nodes. I have
raised the possibilty of moving network devices into the device
namespace, but have had no response.
How can I test if I have devfs compiled into my kernel?
All filesystems built-in or currently loaded are listed in
/proc/filesystems. If you see a devfs entry, then
you know that devfs was compiled into your kernel. If you have
correctly configured and rebuilt your kernel, then devfs will be
built-in. If you think you've configured it in, but
/proc/filesystems doesn't show it, you've made a mistake.
Common mistakes include:
Using a 2.2.x kernel without applying the devfs patch (if you
don't know how to patch your kernel, use 2.4.x instead, don't bother
asking me how to patch)
Forgetting to set CONFIG_EXPERIMENTAL=y
Forgetting to set CONFIG_DEVFS_FS=y
Forgetting to set CONFIG_DEVFS_MOUNT=y (if you want devfs
to be automatically mounted at boot)
Editing your .config manually, instead of using make
config or make xconfig
Forgetting to run make dep; make clean after changing the
configuration and before compiling
Forgetting to compile your kernel and modules
Forgetting to install your kernel
Forgetting to install your modules
Please check twice that you've done all these steps before sending in
a bug report.
How can I test if devfs is mounted on /dev?
The device filesystem will always create an entry called
".devfsd", which is used to communicate with the daemon. Even
if the daemon is not running, this entry will exist. Testing for the
existence of this entry is the approved method of determining if devfs
is mounted or not. Note that the type of entry (i.e. regular file,
character device, named pipe, etc.) may change without notice. Only
the existence of the entry should be relied upon.
When I start devfsd, I see the error:
Error opening file: ".devfsd" No such file or directory?
This means that devfs is not mounted. Make sure you have devfs mounted.
How do I mount devfs?
First make sure you have devfs compiled into your kernel (see
above). Then you will either need to:
set CONFIG_DEVFS_MOUNT=y in your kernel config
pass devfs=mount to your boot loader
mount devfs manually in your boot scripts with:
mount -t none devfs /dev
Mount by volume LABEL=<label> doesn't work with
devfs
Most probably you are not mounting devfs onto /dev. What
happens is that if your kernel config has CONFIG_DEVFS_FS=y
then the contents of /proc/partitions will have the devfs
names (such as scsi/host0/bus0/target0/lun0/part1). The
contents of /proc/partitions are used by mount(8) when
mounting by volume label. If devfs is not mounted on /dev,
then mount(8) will fail to find devices. The solution is to
make sure that devfs is mounted on /dev. See above for how to
do that.
I have extra or incorrect entries in /dev
You may have stale entries in your dev-state area. Check for a
RESTORE configuration line in your devfsd configuration
(typically /etc/devfsd.conf). If you have this line, check
the contents of the specified directory for stale entries. Remove
any entries which are incorrect, then reboot.
I get "Unable to open initial console" messages at boot
This usually happens when you don't have devfs automounted onto
/dev at boot time, and there is no valid
/dev/console entry on your root file-system. Create a valid
/dev/console device node.
Alternatives to devfs
I've attempted to collate all the anti-devfs proposals and explain
their limitations. Under construction.
Why not just pass device create/remove events to a daemon?
Here the suggestion is to develop an API in the kernel so that devices
can register create and remove events, and a daemon listens for those
events. The daemon would then populate/depopulate /dev (which
resides on disc).
This has several limitations:
it only works for modules loaded and unloaded (or devices inserted
and removed) after the kernel has finished booting. Without a database
of events, there is no way the daemon could fully populate
/dev
if you add a database to this scheme, the question is then how to
present that database to user-space. If you make it a list of strings
with embedded event codes which are passed through a pipe to the
daemon, then this is only of use to the daemon. I would argue that the
natural way to present this data is via a filesystem (since many of
the events will be of a hierarchical nature), such as devfs.
Presenting the data as a filesystem makes it easy for the user to see
what is available and also makes it easy to write scripts to scan the
"database"
the tight binding between device nodes and drivers is no longer
possible (requiring the otherwise perfectly avoidable
table lookups)
you cannot catch inode lookup events on /dev which means
that module autoloading requires device nodes to be created. This is a
problem, particularly for drivers where only a few inodes are created
from a potentially large set
this technique can't be used when the root FS is mounted
read-only
Just implement a better scsidev
This suggestion involves taking the scsidev programme and
extending it to scan for all devices, not just SCSI devices. The
scsidev programme works by scanning /proc/scsi
Problems:
the kernel does not currently provide a list of all devices
available. Not all drivers register entries in /proc or
generate kernel messages
there is no uniform mechanism to register devices other than the
devfs API
implementing such an API is then the same as the
proposal above
Put /dev on a ramdisc
This suggestion involves creating a ramdisc and populating it with
device nodes and then mounting it over /dev.
Problems:
this doesn't help when mounting the root filesystem, since you
still need a device node to do that
if you want to use this technique for the root device node as
well, you need to use initrd. This complicates the booting sequence
and makes it significantly harder to administer and configure. The
initrd is essentially opaque, robbing the system administrator of easy
configuration
insufficient information is available to correctly populate the
ramdisc. So we come back to the
proposal above to "solve" this
a ramdisc-based solution would take more kernel memory, since the
backing store would be (at best) normal VFS inodes and dentries, which
take 284 bytes and 112 bytes, respectively, for each entry. Compare
that to 72 bytes for devfs
Do nothing: there's no problem
Sometimes people can be heard to claim that the existing scheme is
fine. This is what they're ignoring:
device number size (8 bits each for major and minor) is a real
limitation, and must be fixed somehow. Systems with large numbers of
SCSI devices, for example, will continue to consume the remaining
unallocated major numbers. USB will also need to push beyond the 8 bit
minor limitation
simply increasing the device number size is insufficient. Apart
from causing a lot of pain, it doesn't solve the management issues
of a /dev with thousands or more device nodes
ignoring the problem of a huge /dev will not make it go
away, and dismisses the legitimacy of a large number of people who
want a dynamic /dev
the standard response then becomes: "write a device management
daemon", which brings us back to the
proposal above
What I don't like about devfs
Here are some common complaints about devfs, and some suggestions and
solutions that may make it more palatable for you. I can't please
everybody, but I do try :-)
I hate the naming scheme
First, remember that no naming scheme will please everybody. You hate
the scheme, others love it. Who's to say who's right and who's wrong?
Ultimately, the person who writes the code gets to choose, and what
exists now is a combination of the choices made by the
devfs author and the
kernel maintainer (Linus).
However, not all is lost. If you want to create your own naming
scheme, it is a simple matter to write a standalone script, hack
devfsd, or write a script called by devfsd. You can create whatever
naming scheme you like.
Further, if you want to remove all traces of the devfs naming scheme
from /dev, you can mount devfs elsewhere (say
/devfs) and populate /dev with links into
/devfs. This population can be automated using devfsd if you
wish.
You can even use the VFS binding facility to make the links, rather
than using symbolic links. This way, you don't even have to see the
"destination" of these symbolic links.
Devfs puts policy into the kernel
There's already policy in the kernel. Device numbers are in fact
policy (why should the kernel dictate what device numbers I use?).
Face it, some policy has to be in the kernel. The real difference
between device names as policy and device numbers as policy is that
no one will use device numbers directly, because device
numbers are devoid of meaning to humans and are ugly. At least with
the devfs device names, (even though you can add your own naming
scheme) some people will use the devfs-supplied names directly. This
offends some people :-)
Devfs is bloatware
This is not even remotely true. As shown above,
both code and data size are quite modest.
How to report bugs
If you have (or think you have) a bug with devfs, please follow the
steps below:
make sure you have enabled debugging output when configuring your
kernel. You will need to set (at least) the following config options:
CONFIG_DEVFS_DEBUG=y
CONFIG_DEBUG_KERNEL=y
CONFIG_DEBUG_SLAB=y
please make sure you have the latest devfs patches applied. The
latest kernel version might not have the latest devfs patches applied
yet (Linus is very busy)
save a copy of your complete kernel logs (preferably by
using the dmesg programme) for later inclusion in your bug
report. You may need to use the -s switch to increase the
internal buffer size so you can capture all the boot messages.
Don't edit or trim the dmesg output
try booting with devfs=dall passed to the kernel boot
command line (read the documentation on your bootloader on how to do
this), and save the result to a file. This may be quite verbose, and
it may overflow the messages buffer, but try to get as much of it as
you can
send a copy of your devfsd configuration file(s)
send the bug report to me first.
Don't expect that I will see it if you post it to the linux-kernel
mailing list. Include all the information listed above, plus
anything else that you think might be relevant. Put the string
devfs somewhere in the subject line, so my mail filters mark
it as urgent
Here is a general guide on how to ask questions in a way that greatly
improves your chances of getting a reply:
http://www.tuxedo.org/~esr/faqs/smart-questions.html. If you have
a bug to report, you should also read
http://www.chiark.greenend.org.uk/~sgtatham/bugs.html.
Strange kernel messages
You may see devfs-related messages in your kernel logs. Below are some
messages and what they mean (and what you should do about them, if
anything).
devfs_register(fred): could not append to parent, err: -17
You need to check what the error code means, but usually 17 means
EEXIST. This means that a driver attempted to create an entry
fred in a directory, but there already was an entry with that
name. This is often caused by flawed boot scripts which untar a bunch
of inodes into /dev, as a way to restore permissions. This
message is harmless, as the device nodes will still
provide access to the driver (unless you use the devfs=only
boot option, which is only for dedicated souls:-). If you want to get
rid of these annoying messages, upgrade to devfsd-v1.3.20 and use the
recommended RESTORE directive to restore permissions.
devfs_mk_dir(bill): using old entry in dir: c1808724 ""
This is similar to the message above, except that a driver attempted
to create a directory named bill, and the parent directory
has an entry with the same name. In this case, to ensure that drivers
continue to work properly, the old entry is re-used and given to the
driver. In 2.5 kernels, the driver is given a NULL entry, and thus,
under rare circumstances, may not create the require device nodes.
The solution is the same as above.
Compilation problems with devfsd
Usually, you can compile devfsd just by typing in
make in the source directory, followed by a make
install (as root). Sometimes, you may have problems, particularly
on broken configurations.
error messages relating to DEVFSD_NOTIFY_DELETE
This happened because you have an ancient set of kernel headers
installed in /usr/include/linux or /usr/src/linux.
Install kernel 2.4.10 or later. You may need to pass the
KERNEL_DIR variable to make (if you did not install
the new kernel sources as /usr/src/linux), or you may copy
the devfs_fs.h file in the kernel source tree into
/usr/include/linux.
-----------------------------------------------------------------------------
Other resources
Douglas Gilbert has written a useful document at
http://www.torque.net/sg/devfs_scsi.html which
explores the SCSI subsystem and how it interacts with devfs
Douglas Gilbert has written another useful document at
http://www.torque.net/scsi/SCSI-2.4-HOWTO/ which
discusses the Linux SCSI subsystem in 2.4.
Johannes Erdfelt has started a discussion paper on Linux and
hot-swap devices, describing what the requirements are for a scalable
solution and how and why he's used devfs+devfsd. Note that this is an
early draft only, available in plain text form at:
http://johannes.erdfelt.com/hotswap.txt.
Johannes has promised a HTML version will follow.
I presented an invited
paper
at the
2nd Annual Storage Management Workshop held in Miamia, Florida,
U.S.A. in October 2000.
-----------------------------------------------------------------------------
Translations of this document
This document has been translated into other languages.
The document master (in English) by rgooch@atnf.csiro.au is
available at
http://www.atnf.csiro.au/~rgooch/linux/docs/devfs.html
A Korean translation by viatoris@nownuri.net is available at
http://your.destiny.pe.kr/devfs/devfs.html
-----------------------------------------------------------------------------
Most flags courtesy of ITA's
Flags of All Countries
used with permission.
Documentation/filesystems/devfs/ToDo deleted 100644 → 0
View file @ d8deac50
Device File System (devfs) ToDo List
Richard Gooch <rgooch@atnf.csiro.au>
3-JUL-2000
This is a list of things to be done for better devfs support in the
Linux kernel. If you'd like to contribute to the devfs, please have a
look at this list for anything that is unallocated. Also, if there are
items missing (surely), please contact me so I can add them to the
list (preferably with your name attached to them:-).
- >256 ptys
Thanks to C. Scott Ananian <cananian@alumni.princeton.edu>
- Amiga floppy driver (drivers/block/amiflop.c)
- Atari floppy driver (drivers/block/ataflop.c)
- SWIM3 (Super Woz Integrated Machine 3) floppy driver (drivers/block/swim3.c)
- Amiga ZorroII ramdisc driver (drivers/block/z2ram.c)
- Parallel port ATAPI CD-ROM (drivers/block/paride/pcd.c)
- Parallel port ATAPI floppy (drivers/block/paride/pf.c)
- AP1000 block driver (drivers/ap1000/ap.c, drivers/ap1000/ddv.c)
- Archimedes floppy (drivers/acorn/block/fd1772.c)
- MFM hard drive (drivers/acorn/block/mfmhd.c)
- I2O block device (drivers/message/i2o/i2o_block.c)
- ST-RAM device (arch/m68k/atari/stram.c)
- Raw devices
Documentation/filesystems/devfs/boot-options deleted 100644 → 0
View file @ d8deac50
/* -*- auto-fill -*- */
Device File System (devfs) Boot Options
Richard Gooch <rgooch@atnf.csiro.au>
18-AUG-2001
When CONFIG_DEVFS_DEBUG is enabled, you can pass several boot options
to the kernel to debug devfs. The boot options are prefixed by
"devfs=", and are separated by commas. Spaces are not allowed. The
syntax looks like this:
devfs=<option1>,<option2>,<option3>
and so on. For example, if you wanted to turn on debugging for module
load requests and device registration, you would do:
devfs=dmod,dreg
You may prefix "no" to any option. This will invert the option.
Debugging Options
=================
These requires CONFIG_DEVFS_DEBUG to be enabled.
Note that all debugging options have 'd' as the first character. By
default all options are off. All debugging output is sent to the
kernel logs. The debugging options do not take effect until the devfs
version message appears (just prior to the root filesystem being
mounted).
These are the options:
dmod print module load requests to <request_module>
dreg print device register requests to <devfs_register>
dunreg print device unregister requests to <devfs_unregister>
dchange print device change requests to <devfs_set_flags>
dilookup print inode lookup requests
diget print VFS inode allocations
diunlink print inode unlinks
dichange print inode changes
dimknod print calls to mknod(2)
dall some debugging turned on
Other Options
=============
These control the default behaviour of devfs. The options are:
mount mount devfs onto /dev at boot time
only disable non-devfs device nodes for devfs-capable drivers
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