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, 27 insertions, 8 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index e24143cc2040..415c2803c0c9 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -968,22 +968,41 @@ static sector_t max_io_len_target_boundary(sector_t sector, struct dm_target *ti
 static sector_t max_io_len(sector_t sector, struct dm_target *ti)
 {
         sector_t len = max_io_len_target_boundary(sector, ti);
+        sector_t offset, max_len;
 
         /*
-         * Does the target need to split even further ?
+         * Does the target need to split even further?
          */
-        if (ti->split_io) {
-                sector_t boundary;
-                sector_t offset = dm_target_offset(ti, sector);
-                boundary = ((offset + ti->split_io) & ~(ti->split_io - 1))
-                           - offset;
-                if (len > boundary)
-                        len = boundary;
+        if (ti->max_io_len) {
+                offset = dm_target_offset(ti, sector);
+                if (unlikely(ti->max_io_len & (ti->max_io_len - 1)))
+                        max_len = sector_div(offset, ti->max_io_len);
+                else
+                        max_len = offset & (ti->max_io_len - 1);
+                max_len = ti->max_io_len - max_len;
+
+                if (len > max_len)
+                        len = max_len;
         }
 
         return len;
 }
 
+int dm_set_target_max_io_len(struct dm_target *ti, sector_t len)
+{
+        if (len > UINT_MAX) {
+                DMERR("Specified maximum size of target IO (%llu) exceeds limit (%u)",
+                      (unsigned long long)len, UINT_MAX);
+                ti->error = "Maximum size of target IO is too large";
+                return -EINVAL;
+        }
+
+        ti->max_io_len = (uint32_t) len;
+
+        return 0;
+}
+EXPORT_SYMBOL_GPL(dm_set_target_max_io_len);
+
 static void __map_bio(struct dm_target *ti, struct bio *clone,
                       struct dm_target_io *tio)
 {