Commit dbda8325 authored by H.J. Thomassen's avatar H.J. Thomassen Committed by Greg Kroah-Hartman

Staging: add cowloop driver

Cowloop is a "copy-on-write" pseudo block driver. It can
be stacked on top of a "real" block driver, and catches
all write operations on their way from the file systems
layer above to the real driver below, effectively shielding
the lower driver from those write accesses. The requests are
then diverted to an ordinary file, located somewhere else
(configurable). Later read requests are checked to see whether
they can be serviced by the "real" block driver below, or
must be pulled in from the diverted location. More information
is on the project's website http://www.ATComputing.nl/cowloop/

From: "H.J. Thomassen" <hjt@ATComputing.nl>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent fa052e91
This diff is collapsed.
/*
** DO NOT MODIFY THESE VALUES (would make old cowfiles unusable)
*/
#define MAPUNIT 1024 /* blocksize for bit in bitmap */
#define MUSHIFT 10 /* bitshift for bit in bitmap */
#define MUMASK 0x3ff /* bitmask for bit in bitmap */
#define COWMAGIC 0x574f437f /* byte-swapped '7f C O W' */
#define COWDIRTY 0x01
#define COWPACKED 0x02
#define COWVERSION 1
struct cowhead
{
int magic; /* identifies a cowfile */
short version; /* version of cowhead */
short flags; /* flags indicating status */
unsigned long mapunit; /* blocksize per bit in bitmap */
unsigned long mapsize; /* total size of bitmap (bytes) */
unsigned long doffset; /* start-offset datablocks in cow */
unsigned long rdoblocks; /* size of related read-only file */
unsigned long rdofingerprint; /* fingerprint of read-only file */
unsigned long cowused; /* number of datablocks used in cow */
};
#define COWDEVDIR "/dev/cow/"
#define COWDEVICE COWDEVDIR "%ld"
#define COWCONTROL COWDEVDIR "ctl"
#define MAXCOWS 1024
#define COWCTL (MAXCOWS-1) /* minor number of /dev/cow/ctl */
#define COWPROCDIR "/proc/cow/"
#define COWPROCFILE COWPROCDIR "%d"
/*
** ioctl related stuff
*/
#define ANYDEV ((unsigned long)-1)
struct cowpair
{
unsigned char *rdofile; /* pathname of the rdofile */
unsigned char *cowfile; /* pathname of the cowfile */
unsigned short rdoflen; /* length of rdofile pathname */
unsigned short cowflen; /* length of cowfile pathname */
unsigned long device; /* requested/returned device number */
};
struct cowwatch
{
int flags; /* request flags */
unsigned long device; /* requested device number */
unsigned long threshold; /* continue if free Kb < threshold */
unsigned long totalkb; /* ret: total filesystem size (Kb) */
unsigned long availkb; /* ret: free filesystem size (Kb) */
};
#define WATCHWAIT 0x01 /* block until threshold reached */
#define COWSYNC _IO ('C', 1)
#define COWMKPAIR _IOW ('C', 2, struct cowpair)
#define COWRMPAIR _IOW ('C', 3, unsigned long)
#define COWWATCH _IOW ('C', 4, struct cowwatch)
#define COWCLOSE _IOW ('C', 5, unsigned long)
#define COWRDOPEN _IOW ('C', 6, unsigned long)
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