Skip to content

L
linux
Commit e6ced426 authored by James Bottomley's avatar James Bottomley
Browse files
Options

[PATCH] scsi_mid_low_api.txt update 

From: Douglas Gilbert <dougg@torque.net>

Attached is an update of the scsi_mid_low_api text
document. The first attachment is a gzipped patch against
lk 2.6.0-test4 and the second one is the file gzipped.

Changes:
   - add "Calling context:" entry to interface functions
   - add "Might block:" entry to mid level functions
   - drop scsi_set_device_offline() + command()
   - change references to reflect transfer of headers to
     include/scsi/scsi_*.h
   - try to define what a "scsi host" is
   - typos + grammar

Thanks to Randy Dunlap, Alan Stern amd Christoph Hellwig
for their input. Comments welcome.
parent 5946da3c
Show whitespace changes
Inline Side-by-side
Showing with 190 additions and 134 deletions
Documentation/scsi/scsi_mid_low_api.txt
View file @ e6ced426
Linux Kernel 2.5 series
Linux Kernel 2.6 series
SCSI mid_level - lower_level driver interface
=============================================
......@@ -6,26 +6,36 @@ Introduction
============
This document outlines the interface between the Linux SCSI mid level and
SCSI lower level drivers. Lower level drivers (LLDs) are variously called
host bus adapter (HBA) drivers, host drivers (HD) or pseudo adapter drivers.
The latter alludes to the fact that a LLD may be a bridge to another IO
subsystem (e.g. the "usb-storage" driver). There can be many LLDs in a
running system, but only one per hardware type. Most LLDs can control one
or more SCSI hosts.
host bus adapter (HBA) drivers and host drivers (HD). A "host" in this
context is a bridge between a computer IO bus (e.g. PCI or ISA) and a
single SCSI initiator device on a SCSI transport. An "initiator" device
(SCSI terminology) sends SCSI commands to "target" SCSI devices (e.g.
disks). There can be many LLDs in a running system, but only one per
hardware type. Most LLDs can control one or more SCSI HBAs. Some HBAs
contain multiple hosts.
In some cases the SCSI transport is an external bus that already has
its own subsystem in Linux (e.g. USB and ieee1394). In such cases the
SCSI subsystem LLD is a software bridge to the other driver subsystem.
Examples are the usb-storage driver (found in the drivers/usb/storage
directory) and the ieee1394/sbp2 driver (found in the drivers/ieee1394
directory).
For example, the aic7xxx LLD controls Adaptec SCSI parallel interface
(SPI) controllers based on that company's 7xxx chip series. The aic7xxx
LLD can be built into the kernel or loaded as a module. There can only be
one aic7xxx LLD running in a Linux system but it may be controlling many
HBAs. These HBAs might be either on PCI daughter-boards or built into
the motherboard (or both). Like most modern HBAs, each aic7xxx host
the motherboard (or both). Some aic7xxx based HBAs are dual controllers
and thus represent two hosts. Like most modern HBAs, each aic7xxx host
has its own PCI device address. [The one-to-one correspondence between
a SCSI host and a PCI device is common but not required (e.g. with
ISA or MCA adapters).]
The SCSI mid level isolates a LLD from other layers such as the SCSI
The SCSI mid level isolates an LLD from other layers such as the SCSI
upper layer drivers and the block layer.
This version of the document roughly matches linux kernel version 2.5.73 .
This version of the document roughly matches linux kernel version 2.6.0-test4.
Documentation
=============
......@@ -52,7 +62,7 @@ file (e.g. the interface functions).
Driver structure
================
Traditionally a LLD for the SCSI subsystem has been at least two files in
Traditionally an LLD for the SCSI subsystem has been at least two files in
the drivers/scsi directory. For example, a driver called "xyz" has a header
file "xyz.h" and a source file "xyz.c". [Actually there is no good reason
why this couldn't all be in one file; the header file is superfluous.] Some
......@@ -65,20 +75,20 @@ When a new LLD is being added to Linux, the following files (found in the
drivers/scsi directory) will need some attention: Makefile and Kconfig .
It is probably best to study how existing LLDs are organized.
As the 2.5 series development kernels evolve, changes are being
introduced into this interface. An example of this is driver
initialization code where there are now 2 models available. The older
one, similar to what was found in the lk 2.4 series, is based on hosts
that are detected at HBA driver load time. This will be referred to
the "passive" initialization model. The newer model allows HBAs to be
hot plugged (and unplugged) during the lifetime of the LLD and will be
referred to as the "hotplug" initialization model. The newer model is
As the 2.5 series development kernels evolve into the 2.6 series
production series, changes are being introduced into this interface. An
example of this is driver initialization code where there are now 2 models
available. The older one, similar to what was found in the lk 2.4 series,
is based on hosts that are detected at HBA driver load time. This will be
referred to the "passive" initialization model. The newer model allows HBAs
to be hot plugged (and unplugged) during the lifetime of the LLD and will
be referred to as the "hotplug" initialization model. The newer model is
preferred as it can handle both traditional SCSI equipment that is
permanently connected as well as modern "SCSI" devices (e.g. USB or
IEEE 1394 connected digital cameras) that are hotplugged. Both
initialization models are discussed in the following sections.
A LLD interfaces to the SCSI subsystem several ways:
An LLD interfaces to the SCSI subsystem several ways:
a) directly invoking functions supplied by the mid level
b) passing a set of function pointers to a registration function
supplied by the mid level. The mid level will then invoke these
......@@ -103,8 +113,8 @@ Those usages in group c) should be handled with care, especially in a
"hotplug" environment. LLDs should be aware of the lifetime of instances
that are shared with the mid level and other layers.
All functions defined within a LLD and all data defined at file scope
should be static. For example the slave_alloc() function in a LLD
All functions defined within an LLD and all data defined at file scope
should be static. For example the slave_alloc() function in an LLD
called "xxx" could be defined as
"static int xxx_slave_alloc(struct scsi_device * sdev) { /* code */ }"
......@@ -116,10 +126,10 @@ the passive initialization model.
Hotplug initialization model
============================
In this model a LLD controls when SCSI hosts are introduced and removed
In this model an LLD controls when SCSI hosts are introduced and removed
from the SCSI subsystem. Hosts can be introduced as early as driver
initialization and removed as late as driver shutdown. Typically a driver
will respond to a sysfs probe() callback that indicates a HBA has been
will respond to a sysfs probe() callback that indicates an HBA has been
detected. After confirming that the new device is one that the LLD wants
to control, the LLD will initialize the HBA and then register a new host
with the SCSI mid level.
......@@ -129,9 +139,9 @@ appropriate IO bus on which it expects to find HBA(s) (e.g. the PCI bus).
This can probably be done via sysfs. Any driver parameters (especially
those that are writable after the driver is loaded) could also be
registered with sysfs at this point. The SCSI mid level first becomes
aware of a LLD when that LLD registers its first HBA.
aware of an LLD when that LLD registers its first HBA.
At some later time, the LLD becomes aware of a HBA and what follows
At some later time, the LLD becomes aware of an HBA and what follows
is a typical sequence of calls between the LLD and the mid level.
This example shows the mid level scanning the newly introduced HBA for 3
scsi devices of which only the first 2 respond:
......@@ -158,7 +168,7 @@ scsi_adjust_queue_depth() in its slave_configure() routine.
*** For scsi devices that the mid level tries to scan but do not
respond, a slave_alloc(), slave_destroy() pair is called.
When a HBA is being removed is could as part of an orderly shutdown
When an HBA is being removed it could be as part of an orderly shutdown
associated with the LLD module being unloaded (e.g. with the "rmmod"
command) or in response to a "hot unplug" indicated by sysfs()'s
remove() callback being invoked. In either case, the sequence is the
......@@ -179,17 +189,17 @@ It may be useful for a LLD to keep track of struct Scsi_Host instances
by the mid-level. struct Scsi_Host instances are freed from
scsi_host_put() when the reference count hits zero.
Hot unplugging a HBA that controls a disk which is processing SCSI
Hot unplugging an HBA that controls a disk which is processing SCSI
commands on a mounted file system is an interesting situation. Reference
counting logic is being introduced into the mid level to cope with many
of the issues involved. See the section on reference counting below.
The hotplug concept may be extended to SCSI devices. Currently, when a
The hotplug concept may be extended to SCSI devices. Currently, when an
HBA is added, the scsi_add_host() function causes a scan for SCSI devices
attached to the HBA's SCSI transport. On newer SCSI transports the HBA
may become aware of a new SCSI device _after_ the scan has completed.
A LLD can use this sequence to make the mid level aware of a SCSI device:
An LLD can use this sequence to make the mid level aware of a SCSI device:
SCSI DEVICE hotplug
LLD mid level LLD
......@@ -200,24 +210,23 @@ scsi_add_device() ------+
slave_configure() [--> scsi_adjust_queue_depth()]
------------------------------------------------------------
In a similar fashion, a LLD may become aware that a SCSI device has been
In a similar fashion, an LLD may become aware that a SCSI device has been
removed (unplugged) or the connection to it has been interrupted. Some
existing SCSI transports (e.g. SPI) may not become aware that a SCSI
device has been removed until a subsequent SCSI command fails which will
probably cause that device to be set offline by the mid level. A LLD that
probably cause that device to be set offline by the mid level. An LLD that
detects the removal of a SCSI device can instigate its removal from
upper layers with this sequence:
SCSI DEVICE hot unplug
LLD mid level LLD
===----------------------=========-----------------===------
scsi_set_device_offline()
scsi_remove_device() -------+
|
slave_destroy()
------------------------------------------------------------
It may be useful for a LLD to keep track of struct scsi_device instances
It may be useful for an LLD to keep track of struct scsi_device instances
(a pointer is passed as the parameter to slave_alloc() and
slave_configure() callbacks). Such instances are "owned" by the mid-level.
struct scsi_device instances are freed after slave_destroy().
......@@ -240,7 +249,7 @@ The scsi_module.c file contains two functions:
- exit_this_scsi_driver() which is executed when the LLD is shut
down (i.e. module unload time)
Note: since these functions are tagged with __init and __exit qualifiers
a LLD should not call them explicitly (since the kernel does that).
an LLD should not call them explicitly (since the kernel does that).
Here is an example of an initialization sequence when two hosts are
detected (so detect() returns 2) and the SCSI bus scan on each host
......@@ -273,7 +282,7 @@ overridden by a slave_configure() supplied by the LLD.
*** For scsi devices that the mid level tries to scan but do not
respond, a slave_alloc(), slave_destroy() pair is called.
Here is a LLD shutdown sequence:
Here is an LLD shutdown sequence:
LLD mid level LLD
===----------------------=========-----------------===------
......@@ -286,13 +295,13 @@ exit_this_scsi_driver() ----+
release() --> scsi_unregister()
------------------------------------------------------------
A LLD need not define slave_destroy() (i.e. it is optional).
An LLD need not define slave_destroy() (i.e. it is optional).
The shortcoming of the "passive initialization model" is that host
registration and de-registration are (typically) tied to LLD initialization
and shutdown. Once the LLD is initialized then a new host that appears
(e.g. via hotplugging) cannot easily be added without a redundant
driver shutdown and re-initialization. It may be possible to write a LLD
driver shutdown and re-initialization. It may be possible to write an LLD
that uses both initialization models.
......@@ -320,7 +329,7 @@ in parallel by these functions.
Conventions
===========
First, Linus Torvald's thoughts on C coding style can be found in the
First, Linus Torvalds's thoughts on C coding style can be found in the
Documentation/CodingStyle file.
Next, there is a movement to "outlaw" typedefs introducing synonyms for
......@@ -329,10 +338,11 @@ the typedefs have been moved to a single file, scsi_typedefs.h to
make their future removal easier, for example:
"typedef struct scsi_host_template Scsi_Host_Template;"
Also, C99 enhancements are encouraged to the extent they are supported
by the relevant gcc compilers. So "//" style comments are encouraged
were appropriate as are C99 style structure and array initializers.
Don't go too far, VLAs are not properly supported yet.
Also, most C99 enhancements are encouraged to the extent they are supported
by the relevant gcc compilers. So C99 style structure and array
initializers are encouraged where appropriate. Don't go too far,
VLAs are not properly supported yet. An exception to this is the use of
"//" style comments; /*...*/ comments are still preferred in Linux.
Well written, tested and documented code, need not be re-formatted to
comply with the above conventions. For example, the aic7xxx driver
......@@ -343,8 +353,8 @@ and Adaptec have their own coding conventions.
Mid level supplied functions
============================
These functions are supplied by the SCSI mid level for use by LLDs.
The names (i.e. entry points) of these functions are exported (in
scsi_syms.c) so a LLD that is a module can access them. The kernel will
The names (i.e. entry points) of these functions are exported (mainly in
scsi_syms.c) so an LLD that is a module can access them. The kernel will
arrange for the SCSI mid level to be loaded and initialized before any LLD
is initialized. The functions below are listed alphabetically and their
names all start with "scsi_".
......@@ -367,7 +377,6 @@ Summary:
scsi_remove_host - detach and remove all SCSI devices owned by host
scsi_report_bus_reset - report scsi _bus_ reset observed
scsi_set_device - place device reference in host structure
scsi_set_device_offline - set device offline then flush its queue
scsi_to_pci_dma_dir - convert SCSI subsystem direction flag to PCI
scsi_to_sbus_dma_dir - convert SCSI subsystem direction flag to SBUS
scsi_track_queue_full - track successive QUEUE_FULL events
......@@ -388,8 +397,10 @@ Details:
* ERR_PTR(-ENODEV) (or some other bent pointer) if something is
* wrong (e.g. no lu responds at given address)
*
* Might block: yes
*
* Notes: This call is usually performed internally during a scsi
* bus scan when a HBA is added (i.e. scsi_add_host()). So it
* bus scan when an HBA is added (i.e. scsi_add_host()). So it
* should only be called if the HBA becomes aware of a new scsi
* device (lu) after scsi_add_host() has completed. If successful
* this call we lead to slave_alloc() and slave_configure() callbacks
......@@ -409,6 +420,8 @@ struct scsi_device * scsi_add_device(struct Scsi_Host *shost,
*
* Returns 0 on success, negative errno of failure (e.g. -ENOMEM)
*
* Might block: no
*
* Notes: Only required in "hotplug initialization model" after a
* successful call to scsi_host_alloc().
*
......@@ -425,9 +438,11 @@ int scsi_add_host(struct Scsi_Host *shost, struct device * dev)
*
* Returns nothing
*
* Might block: no
*
* Notes: Each scsi command has its own timer, and as it is added
* to the queue, we set up the timer. When the command completes,
* we cancel the timer. A LLD can use this function to change
* we cancel the timer. An LLD can use this function to change
* the existing timeout value.
*
* Defined in: drivers/scsi/scsi_error.c
......@@ -448,6 +463,8 @@ void scsi_add_timer(struct scsi_cmnd *scmd, int timeout,
*
* Returns nothing
*
* Might block: no
*
* Notes: Can be invoked any time on a SCSI device controlled by this
* LLD. [Specifically during and after slave_configure() and prior to
* slave_destroy().] Can safely be invoked from interrupt code. Actual
......@@ -468,7 +485,9 @@ void scsi_adjust_queue_depth(struct scsi_device * SDpnt, int tagged,
*
* Returns nothing
*
* Defined in: drivers/scsi/hosts.h .
* Might block: no
*
* Defined in: include/scsi/scsi_host.h .
**/
void scsi_assign_lock(struct Scsi_Host *shost, spinlock_t *lock)
......@@ -479,6 +498,8 @@ void scsi_assign_lock(struct Scsi_Host *shost, spinlock_t *lock)
*
* Returns pointer to partition table, or NULL for failure
*
* Might block: yes
*
* Notes: Caller owns memory returned (free with kfree() )
*
* Defined in: drivers/scsi/scsicam.c
......@@ -493,6 +514,8 @@ unsigned char *scsi_bios_ptable(struct block_device *dev)
*
* Returns nothing
*
* Might block: no
*
* Notes: There is no timer nor any other means by which the requests
* get unblocked other than the LLD calling scsi_unblock_requests().
*
......@@ -508,8 +531,10 @@ void scsi_block_requests(struct Scsi_Host * SHpnt)
* Returns 1 if able to cancel timer else 0 (i.e. too late or already
* cancelled).
*
* Might block: no [may in the future if it invokes del_timer_sync()]
*
* Notes: All commands issued by upper levels already have a timeout
* associated with them. A LLD can use this function to cancel the
* associated with them. An LLD can use this function to cancel the
* timer.
*
* Defined in: drivers/scsi/scsi_error.c
......@@ -525,11 +550,13 @@ int scsi_delete_timer(struct scsi_cmnd *scmd)
*
* Returns pointer to new Scsi_Host instance or NULL on failure
*
* Notes: When this call returns to the LLDD, the SCSI bus scan on
* Might block: yes
*
* Notes: When this call returns to the LLD, the SCSI bus scan on
* this host has _not_ yet been done.
* The hostdata array (by default zero length) is a per host scratch
* area for the LLD.
* Both associated refcounting objects have there refcount set to 1.
* Both associated refcounting objects have their refcount set to 1.
*
* Defined in: drivers/scsi/hosts.c .
**/
......@@ -542,6 +569,8 @@ struct Scsi_Host * scsi_host_alloc(struct scsi_host_template *, int xtr_bytes)
*
* Returns nothing
*
* Might block: currently may block but may be changed to not block
*
* Notes: Actually increments the counts in two sub-objects
*
* Defined in: drivers/scsi/hosts.c
......@@ -555,6 +584,8 @@ void scsi_host_get(struct Scsi_Host *shost)
*
* Returns nothing
*
* Might block: currently may block but may be changed to not block
*
* Notes: Actually decrements the counts in two sub-objects. If the
* latter refcount reaches 0, the Scsi_Host instance is freed.
* The LLD need not worry exactly when the Scsi_Host instance is
......@@ -576,6 +607,8 @@ void scsi_host_put(struct Scsi_Host *shost)
*
* Returns 0 on success, -1 on failure
*
* Might block: no
*
* Notes: Caller owns memory returned (free with kfree() )
*
* Defined in: drivers/scsi/scsicam.c
......@@ -592,7 +625,9 @@ int scsi_partsize(unsigned char *buf, unsigned long capacity,
*
* Returns pointer to new Scsi_Host instance or NULL on failure
*
* Notes: When this call returns to the LLDD, the SCSI bus scan on
* Might block: yes
*
* Notes: When this call returns to the LLD, the SCSI bus scan on
* this host has _not_ yet been done.
* The hostdata array (by default zero length) is a per host scratch
* area for the LLD.
......@@ -608,13 +643,15 @@ struct Scsi_Host * scsi_register(struct scsi_host_template *, int xtr_bytes)
*
* Returns value: 0 on success, -EINVAL if device not attached
*
* Notes: If a LLD becomes aware that a scsi device (lu) has
* Might block: yes
*
* Notes: If an LLD becomes aware that a scsi device (lu) has
* been removed but its host is still present then it can request
* the removal of that scsi device. If successful this call will
* lead to the slave_destroy() callback being invoked. sdev is an
* invalid pointer after this call.
*
* Defined in: drivers/scsi/scsi_scan.c .
* Defined in: drivers/scsi/scsi_sysfs.c .
**/
int scsi_remove_device(struct scsi_device *sdev)
......@@ -625,6 +662,8 @@ int scsi_remove_device(struct scsi_device *sdev)
*
* Returns value: 0 on success, 1 on failure (e.g. LLD busy ??)
*
* Might block: yes
*
* Notes: Should only be invoked if the "hotplug initialization
* model" is being used. It should be called _prior_ to
* scsi_unregister().
......@@ -641,13 +680,15 @@ int scsi_remove_host(struct Scsi_Host *shost)
*
* Returns nothing
*
* Might block: no
*
* Notes: This only needs to be called if the reset is one which
* originates from an unknown location. Resets originated by the
* mid level itself don't need to call this, but there should be
* no harm. The main purpose of this is to make sure that a
* CHECK_CONDITION is properly treated.
*
* Defined in: drivers/scsi/scsi_lib.c .
* Defined in: drivers/scsi/scsi_error.c .
**/
void scsi_report_bus_reset(struct Scsi_Host * shost, int channel)
......@@ -659,24 +700,11 @@ void scsi_report_bus_reset(struct Scsi_Host * shost, int channel)
*
* Returns nothing
*
* Defined in: drivers/scsi/hosts.h .
**/
void scsi_set_device(struct Scsi_Host * shost, struct device * dev)
/**
* scsi_set_device_offline - set device offline then flush its queue
* @sdev: a pointer to a scsi device instance to be set offline
*
* Returns nothing
* Might block: no
*
* Notes: Commands that are currently active on the scsi device have
* their timers cancelled and are transferred to the host's
* "eh" list for cancellation.
* Defined in: drivers/scsi/scsi.c .
* Defined in: include/scsi/scsi_host.h .
**/
void scsi_set_device_offline(struct scsi_device * sdev)
void scsi_set_device(struct Scsi_Host * shost, struct device * dev)
/**
......@@ -688,6 +716,11 @@ void scsi_set_device_offline(struct scsi_device * sdev)
* PCI_DMA_BIDIRECTIONAL given SCSI_DATA_UNKNOWN
* else returns PCI_DMA_NONE
*
* Might block: no
*
* Notes: The SCSI subsystem now uses the same values for these
* constants as the PCI subsystem so this function is a nop.
*
* Defined in: drivers/scsi/scsi.h .
**/
int scsi_to_pci_dma_dir(unsigned char scsi_data_direction)
......@@ -702,6 +735,11 @@ int scsi_to_pci_dma_dir(unsigned char scsi_data_direction)
* SBUS_DMA_BIDIRECTIONAL given SCSI_DATA_UNKNOWN
* else returns SBUS_DMA_NONE
*
* Notes: The SCSI subsystem now uses the same values for these
* constants as the SBUS subsystem so this function is a nop.
*
* Might block: no
*
* Defined in: drivers/scsi/scsi.h .
**/
int scsi_to_sbus_dma_dir(unsigned char scsi_data_direction)
......@@ -720,6 +758,8 @@ int scsi_to_sbus_dma_dir(unsigned char scsi_data_direction)
* -1 - drop back to untagged operation using host->cmd_per_lun
* as the untagged command depth
*
* Might block: no
*
* Notes: LLDs may call this at any time and we will do "The Right
* Thing"; interrupt context safe.
*
......@@ -735,6 +775,8 @@ int scsi_track_queue_full(Scsi_Device *SDptr, int depth)
*
* Returns nothing
*
* Might block: no
*
* Defined in: drivers/scsi/scsi_lib.c .
**/
void scsi_unblock_requests(struct Scsi_Host * SHpnt)
......@@ -746,9 +788,12 @@ void scsi_unblock_requests(struct Scsi_Host * SHpnt)
*
* Returns nothing
*
* Notes: Should only be invoked if the "hotplug initialization
* model" is being used. It should be called _after_
* scsi_remove_host(). The shp pointer is invalid after this call.
* Might block: no
*
* Notes: Should not be invoked if the "hotplug initialization
* model" is being used. Called internally by exit_this_scsi_driver()
* in the "passive initialization model". Hence a LLD has no need to
* call this function directly.
*
* Defined in: drivers/scsi/hosts.c .
**/
......@@ -766,21 +811,21 @@ Some are mandatory. Interface functions should be declared static. The
accepted convention is that driver "xyz" will declare its slave_configure()
function as:
static int xyz_slave_configure(struct scsi_device * sdev);
and so forth for all interface functions listed below.
A pointer to this function should be placed in the 'slave_configure' member
of a "struct scsi_host_template" instance. A pointer to such an instance
should passed to the mid level's scsi_host_alloc() [or scsi_register() /
should be passed to the mid level's scsi_host_alloc() [or scsi_register() /
init_this_scsi_driver()].
The interface functions are also described in the hosts.h file immediately
above their definition point in "struct scsi_host_template". In some cases
more detail is given in hosts.h than below.
The interface functions are also described in the include/scsi/scsi_host.h
file immediately above their definition point in "struct scsi_host_template".
In some cases more detail is given in scsi_host.h than below.
The interface functions are listed below in alphabetical order.
Summary:
bios_param - fetch head, sector, cylinder info for a disk
command - send scsi command to device, wait for reply
detect - detects HBAs this driver wants to control
eh_abort_handler - abort given command
eh_bus_reset_handler - issue SCSI bus reset
......@@ -801,7 +846,8 @@ Details:
/**
* bios_param - fetch head, sector, cylinder info for a disk
* @sdev: pointer to scsi device context (defined in scsi.h)
* @sdev: pointer to scsi device context (defined in
* include/scsi/scsi_device.h)
* @bdev: pointer to block device context (defined in fs.h)
* @capacity: device size (in 512 byte sectors)
* @params: three element array to place output:
......@@ -813,6 +859,8 @@ Details:
*
* Locks: none
*
* Calling context: process (sd)
*
* Notes: an arbitrary geometry (based on READ CAPACITY) is used
* if this function is not provided. The params array is
* pre-initialized with made up values just in case this function
......@@ -824,26 +872,6 @@ Details:
sector_t capacity, int params[3])
/**
* command - send scsi command to device, wait for reply
* @scp: pointer to scsi command object
*
* Returns an int with four component bytes: scsi_byte, msg_byte,
* host_byte, driver_byte (status_byte is in the lsb). A value of
* 0 is an unqualified success.
*
* Locks: struct Scsi_Host::host_lock held on entry (with "irqsave")
* and is expected to be held on return.
*
* Notes: Drivers tend to be dropping support for this function and
* supporting queuecommand() instead.
*
* Defined in: LLD (if struct Scsi_Host::can_queue can ever by cleared
* (zero) then this function is required)
**/
int command(struct scsi_cmnd * scp)
/**
* detect - detects HBAs this driver wants to control
* @shtp: host template for this driver.
......@@ -853,6 +881,8 @@ Details:
*
* Locks: none held
*
* Calling context: process [invoked from init_this_scsi_driver()]
*
* Notes: First function called from the SCSI mid level on this
* driver. Upper level drivers (e.g. sd) may not (yet) be present.
* For each host found, this method should call scsi_register()
......@@ -873,6 +903,8 @@ Details:
* Locks: struct Scsi_Host::host_lock held (with irqsave) on entry
* and assumed to be held on return.
*
* Calling context: kernel thread
*
* Notes: Invoked from scsi_eh thread. No other commands will be
* queued on current host during eh.
*
......@@ -890,6 +922,8 @@ Details:
* Locks: struct Scsi_Host::host_lock held (with irqsave) on entry
* and assumed to be held on return.
*
* Calling context: kernel thread
*
* Notes: Invoked from scsi_eh thread. No other commands will be
* queued on current host during eh.
*
......@@ -907,6 +941,8 @@ Details:
* Locks: struct Scsi_Host::host_lock held (with irqsave) on entry
* and assumed to be held on return.
*
* Calling context: kernel thread
*
* Notes: Invoked from scsi_eh thread. No other commands will be
* queued on current host during eh.
*
......@@ -924,6 +960,8 @@ Details:
* Locks: struct Scsi_Host::host_lock held (with irqsave) on entry
* and assumed to be held on return.
*
* Calling context: kernel thread
*
* Notes: Invoked from scsi_eh thread. No other commands will be
* queued on current host during eh.
* With the default eh_strategy in place, if none of the _abort_,
......@@ -944,6 +982,8 @@ Details:
*
* Locks: none
*
* Calling context: kernel thread
*
* Notes: Invoked from scsi_eh thread. LLD supplied alternate to
* scsi_unjam_host() found in scsi_error.c
*
......@@ -963,6 +1003,8 @@ Details:
*
* Locks: none
*
* Calling context: process
*
* Notes: Often supplies PCI or ISA information such as IO addresses
* and interrupt numbers. If not supplied struct Scsi_Host::name used
* instead. It is assumed the returned information fits on one line
......@@ -994,6 +1036,8 @@ Details:
*
* Locks: none
*
* Calling context: process
*
* Notes: The SCSI subsystem uses a "trickle down" ioctl model.
* The user issues an ioctl() against an upper level driver
* (e.g. /dev/sdc) and if the upper level driver doesn't recognize
......@@ -1031,7 +1075,10 @@ Details:
*
* Locks: none held
*
* Notes: Driven from scsi_proc.c which interfaces to proc_fs
* Calling context: process
*
* Notes: Driven from scsi_proc.c which interfaces to proc_fs. proc_fs
* support can now be configured out of the scsi subsystem.
*
* Optionally defined in: LLD
**/
......@@ -1046,31 +1093,33 @@ Details:
*
* Returns 0 on success and 1 if the LLD or the HBA is busy (i.e. run
* out of resources to queue further commands). Other types of errors
* are flagged by setting struct scsi_cmnd:result to an appropriate
* value, invoking the 'done' callback, and then returning 0.
* that are detected immediately are flagged by setting scp->result
* to an appropriate value, invoking the 'done' callback, and then
* returning 0 from this function. If the command is not performed
* immediately (and the LLD is starting (or will start) the given
* command) then this function should place 0 in scp->result and
* return 0.
*
* Locks: struct Scsi_Host::host_lock held on entry (with "irqsave")
* and is expected to be held on return.
*
* Calling context: in interrupt (soft irq) or process context
*
* Notes: This function should be relatively fast. Normally it will
* not wait for IO to complete. Hence the 'done' callback is invoked
* (often directly from an interrupt service routine) sometime after
* this command has returned. In some cases (e.g. pseudo adapter
* (often directly from an interrupt service routine) some time after
* this function has returned. In some cases (e.g. pseudo adapter
* drivers that manufacture the response to a SCSI INQUIRY)
* the 'done' callback may be invoked before this function returns.
* If the 'done' callback is not invoked within a certain period
* the SCSI mid level will commence error processing.
* The integer with 4 component bytes that command() uses as its
* return value should be generated by this function. However, in
* this case, it should be placed in scp->result before this function
* returns.
* If a status of CHECK CONDITION is placed in "result" when the
* 'done' callback is invoked, then the LLD driver should
* perform autosense and fill in the struct scsi_cmnd::sense_buffer
* array.
* array. The scsi_cmnd::sense_buffer array is zeroed prior to
* the mid level queuing a command to an LLD.
*
* Defined in: LLD (required if if struct Scsi_Host::can_queue is ever
* non-zero)
* Defined in: LLD
**/
int queuecommand(struct scsi_cmnd * scp,
void (*done)(struct scsi_cmnd *))
......@@ -1084,6 +1133,8 @@ Details:
*
* Locks: none held
*
* Calling context: process
*
* Notes: Invoked from scsi_module.c's exit_this_scsi_driver().
* LLD's implementation of this function should call
* scsi_unregister(shp) prior to returning.
......@@ -1105,13 +1156,15 @@ Details:
*
* Locks: none
*
* Calling context: process
*
* Notes: Allows the driver to allocate any resources for a device
* prior to its initial scan. The corresponding scsi device may not
* exist but the mid level is just about to scan for it (i.e. send
* and INQUIRY command plus ...). If a device is found then
* slave_configure() will be called while if a device is not found
* slave_destroy() is called.
* For more details see the hosts.h file.
* For more details see the include/scsi/scsi_host.h file.
*
* Optionally defined in: LLD
**/
......@@ -1130,9 +1183,11 @@ Details:
*
* Locks: none
*
* Calling context: process
*
* Notes: Allows the driver to inspect the response to the initial
* INQUIRY done by the scanning code and take appropriate action.
* For more details see the hosts.h file.
* For more details see the include/scsi/scsi_host.h file.
*
* Optionally defined in: LLD
**/
......@@ -1148,6 +1203,8 @@ Details:
*
* Locks: none
*
* Calling context: process
*
* Notes: Mid level structures for given device are still in place
* but are about to be torn down. Any per device resources allocated
* by this driver for given device should be freed now. No further
......@@ -1177,17 +1234,17 @@ Member of interest:
"proc_name" should only contain characters acceptable
to a Unix file name.
(*queuecommand)() - primary callback that the mid level uses to inject
SCSI commands into a LLD.
The structure is defined and commented in hosts.h
SCSI commands into an LLD.
The structure is defined and commented in include/scsi/scsi_host.h
*** In extreme situations a single driver may have several instances
if it controls several different classes of hardware (e.g. a LLD
if it controls several different classes of hardware (e.g. an LLD
that handles both ISA and PCI cards and has a separate instance of
struct scsi_host_template for each class).
struct Scsi_Host
----------------
There is one struct Scsi_Host instance per host (HBA) that a LLD
There is one struct Scsi_Host instance per host (HBA) that an LLD
controls. The struct Scsi_Host structure has many members in common
with "struct scsi_host_template". When a new struct Scsi_Host instance
is created (in scsi_host_alloc() in hosts.c) those common members are
......@@ -1197,23 +1254,21 @@ of interest:
this host. Issued in ascending order from 0 (and the
positioning can be influenced by the scsihosts
kernel boot (or module) parameter)
can_queue - 0->use command(), greater than 0->use queuecommand() and
do not send more than can_queue commands to the adapter.
can_queue - must be greater than 0; do not send more than can_queue
commands to the adapter.
this_id - scsi id of host (scsi initiator) or -1 if not known
sg_tablesize - maximum scatter gather elements allowed by host.
0 implies scatter gather not supported by host
max_sectors - maximum number of sectors (usually 512 bytes) allowed
in a single SCSI command. 0 implies no maximum.
cmd_per_lun - maximum number of command that can be queued on devices
cmd_per_lun - maximum number of commands that can be queued on devices
controlled by the host. Overridden by LLD calls to
scsi_adjust_queue_depth().
unchecked_isa_dma - 1->only use bottom 16 MB of ram (ISA DMA addressing
restriction), 0->can use full 32 bit (or better) DMA
unchecked_isa_dma - 1=>only use bottom 16 MB of ram (ISA DMA addressing
restriction), 0=>can use full 32 bit (or better) DMA
address space
use_clustering - 1->SCSI commands in mid level's queue can be merged,
0->disallow SCSI command merging
highmem_io - 1->can DMA in to or out of high memory,
0->use bounce buffers if data is in high memory
use_clustering - 1=>SCSI commands in mid level's queue can be merged,
0=>disallow SCSI command merging
hostt - pointer to driver's struct scsi_host_template from which
this struct Scsi_Host instance was spawned
sh_list - a double linked list of pointers to all struct Scsi_Host
......@@ -1223,14 +1278,14 @@ of interest:
hostdata[0] - area reserved for LLD at end of struct Scsi_Host. Size
is set by the second argument (named 'xtr_bytes') to
scsi_host_alloc() or scsi_register().
The structure is defined in hosts.h
The structure is defined in include/scsi/scsi_host.h
struct scsi_device
------------------
Generally, there is one instance of this structure for each SCSI logical unit
on a host. Scsi devices connected to a host are uniquely identified by a
channel number, target id and logical unit number (lun).
The structure is defined in scsi.h
The structure is defined in include/scsi/scsi_device.h
struct scsi_cmnd
----------------
......@@ -1239,7 +1294,7 @@ back to the mid level. The SCSI mid level will ensure that no more SCSI
commands become queued against the LLD than are indicated by
scsi_adjust_queue_depth() (or struct Scsi_Host::cmd_per_lun). There will
be at least one instance of struct scsi_cmnd available for each SCSI device.
The structure is defined in scsi.h
The structure is defined in include/scsi/scsi_cmnd.h
Locks
......@@ -1295,9 +1350,9 @@ The struct scsi_host_template::use_new_eh_code flag has been removed.
In the 2.4 series the SCSI subsystem configuration descriptions were
aggregated with the configuration descriptions from all other Linux
subsystems in the Documentation/Configure.help file. In the 2.5 series,
the SCSI subsystem now has its own (much smaller) drivers/scsi/Config.help
file.
subsystems in the Documentation/Configure.help file. In the 2.6 series,
the SCSI subsystem now has its own (much smaller) drivers/scsi/Kconfig
file that contains both configuration and help information.
struct SHT has been renamed to struct scsi_host_template.
......@@ -1314,8 +1369,9 @@ The following people have contributed to this document:
Christoph Hellwig <hch@infradead.org>
Doug Ledford <dledford@redhat.com>
Andries Brouwer <Andries.Brouwer@cwi.nl>
Randy Dunlap <rddunlap@osdl.org>
Douglas Gilbert
dgilbert@interlog.com
18th June 2003
29th August 2003
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment
GitLab Nexedi Edition | About GitLab | About Nexedi | 沪ICP备2021021310号-2 | 沪ICP备2021021310号-7