[PATCH] dm: bio split bvec fix

The code that handles bios that span table target boundaries by breaking
them up into smaller bios will not split an individual struct bio_vec into
more than two pieces.  Sometimes more than that are required.

This patch adds a loop to break the second piece up into as many pieces as
are necessary.

Cc: "Abhishek Gupta" <abhishekgupt@gmail.com>
Cc: Dan Smith <danms@us.ibm.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/md/dm.c

@@ -533,30 +533,35 @@ static void __clone_and_map(struct clone_info *ci)
 
 	} else {
 		/*
-		 * Create two copy bios to deal with io that has
-		 * been split across a target.
+		 * Handle a bvec that must be split between two or more targets.
 		 */
 		struct bio_vec *bv = bio->bi_io_vec + ci->idx;
+		sector_t remaining = to_sector(bv->bv_len);
+		unsigned int offset = 0;
 
-		clone = split_bvec(bio, ci->sector, ci->idx,
-				   bv->bv_offset, max);
-		__map_bio(ti, clone, tio);
+		do {
+			if (offset) {
+				ti = dm_table_find_target(ci->map, ci->sector);
+				max = max_io_len(ci->md, ci->sector, ti);
 
-		ci->sector += max;
-		ci->sector_count -= max;
-		ti = dm_table_find_target(ci->map, ci->sector);
-
-		len = to_sector(bv->bv_len) - max;
-		clone = split_bvec(bio, ci->sector, ci->idx,
-				   bv->bv_offset + to_bytes(max), len);
-		tio = alloc_tio(ci->md);
-		tio->io = ci->io;
-		tio->ti = ti;
-		memset(&tio->info, 0, sizeof(tio->info));
-		__map_bio(ti, clone, tio);
+				tio = alloc_tio(ci->md);
+				tio->io = ci->io;
+				tio->ti = ti;
+				memset(&tio->info, 0, sizeof(tio->info));
+			}
+
+			len = min(remaining, max);
+
+			clone = split_bvec(bio, ci->sector, ci->idx,
+					   bv->bv_offset + offset, len);
+
+			__map_bio(ti, clone, tio);
+
+			ci->sector += len;
+			ci->sector_count -= len;
+			offset += to_bytes(len);
+		} while (remaining -= len);
 
-		ci->sector += len;
-		ci->sector_count -= len;
 		ci->idx++;
 	}
 }