[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>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index b42e71bb9e6722f71ce332948b78e6732f531dae..d8544e1a4c1f96a0f79490226d833880ee3c38a5 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -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();
        }
 }
 

diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index 81c98d6e35e97c6489b51ed9e83fd0117ea175e1..293d5ce62a2150793b787cdd7a683f931c9eeeb3 100644 (file)
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -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
  */

diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 9194ff2d08c0c7ef411fd41eaa690681c91336c3..2e5c42346c381a0857963ee79aacffec97eaff9c 100644 (file)
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -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);