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Subject[PATCH 04/11] dm: map and endio return code clarification
From: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>

This patch tightens 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

Index: linux-2.6.19-rc6/drivers/md/dm.c
===================================================================
--- linux-2.6.19-rc6.orig/drivers/md/dm.c 2006-11-22 17:26:57.000000000 +0000
+++ linux-2.6.19-rc6/drivers/md/dm.c 2006-11-22 17:26:58.000000000 +0000
@@ -482,9 +482,13 @@ static int clone_endio(struct bio *bio,
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 *
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 *
clone->bi_private = md->bs;
bio_put(clone);
free_tio(md, tio);
+ } else if (r) {
+ DMWARN("unimplemented target map return value: %d", r);
+ BUG();
}
}

Index: linux-2.6.19-rc6/drivers/md/dm.h
===================================================================
--- linux-2.6.19-rc6.orig/drivers/md/dm.h 2006-11-22 17:26:57.000000000 +0000
+++ linux-2.6.19-rc6/drivers/md/dm.h 2006-11-22 17:26:58.000000000 +0000
@@ -33,6 +33,17 @@
#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
*/
#define DM_SUSPEND_LOCKFS_FLAG (1 << 0)
Index: linux-2.6.19-rc6/include/linux/device-mapper.h
===================================================================
--- linux-2.6.19-rc6.orig/include/linux/device-mapper.h 2006-11-22 17:26:57.000000000 +0000
+++ linux-2.6.19-rc6/include/linux/device-mapper.h 2006-11-22 17:26:58.000000000 +0000
@@ -39,7 +39,7 @@ typedef void (*dm_dtr_fn) (struct dm_tar
* 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);
-
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