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[PATCH] dm: map and endio return code clarification 

Tighten the use of return values from the target map and end_io functions.
Values of 2 and above are now explictly reserved for future use.  There are no
existing targets using such values.

The patch has no effect on existing behaviour.

o Reserve return values of 2 and above from target map functions.
  Any positive value currently indicates "mapping complete", but all
  existing drivers use the value 1.  We now make that a requirement
  so we can assign new meaning to higher values in future.

  The new definition of return values from target map functions is:
      < 0 : error
      = 0 : The target will handle the io (DM_MAPIO_SUBMITTED).
      = 1 : Mapping completed (DM_MAPIO_REMAPPED).
      > 1 : Reserved (undefined).  Previously this was the same as '= 1'.

o Reserve return values of 2 and above from target end_io functions
  for similar reasons.
  DM_ENDIO_INCOMPLETE is introduced for a return value of 1.

Test results:

  I have tested by using the multipath target.

  I/Os succeed when valid paths exist.

  I/Os are queued in the multipath target when there are no valid paths and
queue_if_no_path is set.

  I/Os fail when there are no valid paths and queue_if_no_path is not set.

Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Cc: dm-devel@redhat.com
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Kiyoshi Ueda 2006-12-08 02:41:05 -08:00 committed by Linus Torvalds
parent a3d77d35be
commit 45cbcd7983
3 changed files with 22 additions and 4 deletions
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13
drivers/md/dm.c
View File

@ -482,9 +482,13 @@ static int clone_endio(struct bio *bio, unsigned int done, int error)
r = endio(tio->ti, bio, error, &tio->info);
if (r < 0)
error = r;
else if (r > 0)
/* the target wants another shot at the io */
else if (r == DM_ENDIO_INCOMPLETE)
/* The target will handle the io */
return 1;
else if (r) {
DMWARN("unimplemented target endio return value: %d", r);
BUG();
}
}
dec_pending(tio->io, error);
@ -542,7 +546,7 @@ static void __map_bio(struct dm_target *ti, struct bio *clone,
atomic_inc(&tio->io->io_count);
sector = clone->bi_sector;
r = ti->type->map(ti, clone, &tio->info);
if (r > 0) {
if (r == DM_MAPIO_REMAPPED) {
/* the bio has been remapped so dispatch it */
blk_add_trace_remap(bdev_get_queue(clone->bi_bdev), clone,
@ -560,6 +564,9 @@ static void __map_bio(struct dm_target *ti, struct bio *clone,
clone->bi_private = md->bs;
bio_put(clone);
free_tio(md, tio);
} else if (r) {
DMWARN("unimplemented target map return value: %d", r);
BUG();
}
}

11
drivers/md/dm.h
View File

@ -32,6 +32,17 @@
#define SECTOR_SHIFT 9
/*
* Definitions of return values from target end_io function.
*/
#define DM_ENDIO_INCOMPLETE 1
/*
* Definitions of return values from target map function.
*/
#define DM_MAPIO_SUBMITTED 0
#define DM_MAPIO_REMAPPED 1
/*
* Suspend feature flags
*/

2
include/linux/device-mapper.h
View File

@ -39,7 +39,7 @@ typedef void (*dm_dtr_fn) (struct dm_target *ti);
* The map function must return:
* < 0: error
* = 0: The target will handle the io by resubmitting it later
* > 0: simple remap complete
* = 1: simple remap complete
*/
typedef int (*dm_map_fn) (struct dm_target *ti, struct bio *bio,
union map_info *map_context);