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, 15 insertions, 12 deletions

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index a228c20e40b3..6c0f3e33923a 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -691,7 +691,7 @@ static int dm_add_exception(void *context, chunk_t old, chunk_t new)
  * Return a minimum chunk size of all snapshots that have the specified origin.
  * Return zero if the origin has no snapshots.
  */
-static sector_t __minimum_chunk_size(struct origin *o)
+static uint32_t __minimum_chunk_size(struct origin *o)
 {
         struct dm_snapshot *snap;
         unsigned chunk_size = 0;
@@ -701,7 +701,7 @@ static sector_t __minimum_chunk_size(struct origin *o)
                         chunk_size = min_not_zero(chunk_size,
                                                   snap->store->chunk_size);
 
-        return chunk_size;
+        return (uint32_t) chunk_size;
 }
 
 /*
@@ -1172,7 +1172,10 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
                 ti->error = "Chunk size not set";
                 goto bad_read_metadata;
         }
-        ti->split_io = s->store->chunk_size;
+
+        r = dm_set_target_max_io_len(ti, s->store->chunk_size);
+        if (r)
+                goto bad_read_metadata;
 
         return 0;
 
@@ -1239,7 +1242,7 @@ static void __handover_exceptions(struct dm_snapshot *snap_src,
         snap_dest->store->snap = snap_dest;
         snap_src->store->snap = snap_src;
 
-        snap_dest->ti->split_io = snap_dest->store->chunk_size;
+        snap_dest->ti->max_io_len = snap_dest->store->chunk_size;
         snap_dest->valid = snap_src->valid;
 
         /*
@@ -1817,9 +1820,9 @@ static void snapshot_resume(struct dm_target *ti)
         up_write(&s->lock);
 }
 
-static sector_t get_origin_minimum_chunksize(struct block_device *bdev)
+static uint32_t get_origin_minimum_chunksize(struct block_device *bdev)
 {
-        sector_t min_chunksize;
+        uint32_t min_chunksize;
 
         down_read(&_origins_lock);
         min_chunksize = __minimum_chunk_size(__lookup_origin(bdev));
@@ -1838,9 +1841,9 @@ static void snapshot_merge_resume(struct dm_target *ti)
         snapshot_resume(ti);
 
         /*
-         * snapshot-merge acts as an origin, so set ti->split_io
+         * snapshot-merge acts as an origin, so set ti->max_io_len
          */
-        ti->split_io = get_origin_minimum_chunksize(s->origin->bdev);
+        ti->max_io_len = get_origin_minimum_chunksize(s->origin->bdev);
 
         start_merge(s);
 }
@@ -2073,12 +2076,12 @@ static int origin_write_extent(struct dm_snapshot *merging_snap,
         struct origin *o;
 
         /*
-         * The origin's __minimum_chunk_size() got stored in split_io
+         * The origin's __minimum_chunk_size() got stored in max_io_len
          * by snapshot_merge_resume().
          */
         down_read(&_origins_lock);
         o = __lookup_origin(merging_snap->origin->bdev);
-        for (n = 0; n < size; n += merging_snap->ti->split_io)
+        for (n = 0; n < size; n += merging_snap->ti->max_io_len)
                 if (__origin_write(&o->snapshots, sector + n, NULL) ==
                     DM_MAPIO_SUBMITTED)
                         must_wait = 1;
@@ -2138,14 +2141,14 @@ static int origin_map(struct dm_target *ti, struct bio *bio,
 }
 
 /*
- * Set the target "split_io" field to the minimum of all the snapshots'
+ * Set the target "max_io_len" field to the minimum of all the snapshots'
  * chunk sizes.
  */
 static void origin_resume(struct dm_target *ti)
 {
         struct dm_dev *dev = ti->private;
 
-        ti->split_io = get_origin_minimum_chunksize(dev->bdev);
+        ti->max_io_len = get_origin_minimum_chunksize(dev->bdev);
 }
 
 static int origin_status(struct dm_target *ti, status_type_t type, char *result,