dm: support non power of two target max_io_len

Remove the restriction that limits a target's specified maximum incoming
I/O size to be a power of 2.

Rename this setting from 'split_io' to the less-ambiguous 'max_io_len'.
Change it from sector_t to uint32_t, which is plenty big enough, and
introduce a wrapper function dm_set_target_max_io_len() to set it.
Use sector_div() to process it now that it is not necessarily a power of 2.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index d70cbb2ada25..b19c1e189a68 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -186,8 +186,8 @@ struct dm_target {
 	sector_t begin;
 	sector_t len;
 
-	/* Always a power of 2 */
-	sector_t split_io;
+	/* If non-zero, maximum size of I/O submitted to a target. */
+	uint32_t max_io_len;
 
 	/*
 	 * A number of zero-length barrier requests that will be submitted
@@ -358,6 +358,11 @@ void dm_table_add_target_callbacks(struct dm_table *t, struct dm_target_callback
 int dm_table_complete(struct dm_table *t);
 
 /*
+ * Target may require that it is never sent I/O larger than len.
+ */
+int __must_check dm_set_target_max_io_len(struct dm_target *ti, sector_t len);
+
+/*
  * Table reference counting.
  */
 struct dm_table *dm_get_live_table(struct mapped_device *md);