dm io: handle empty barriers

Accept empty barriers in dm-io.

dm-io will process empty write barrier requests just like the other
read/write requests.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index f6a714c..10f457c 100644 (file)
--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -309,7 +309,11 @@ static void do_region(int rw, unsigned region, struct dm_io_region *where,
        unsigned num_bvecs;
        sector_t remaining = where->count;
 
-       while (remaining) {
+       /*
+        * where->count may be zero if rw holds a write barrier and we
+        * need to send a zero-sized barrier.
+        */
+       do {
                /*
                 * Allocate a suitably sized-bio.
                 */
@@ -339,7 +343,7 @@ static void do_region(int rw, unsigned region, struct dm_io_region *where,
 
                atomic_inc(&io->count);
                submit_bio(rw, bio);
-       }
+       } while (remaining);
 }
 
 static void dispatch_io(int rw, unsigned int num_regions,
@@ -360,7 +364,7 @@ static void dispatch_io(int rw, unsigned int num_regions,
         */
        for (i = 0; i < num_regions; i++) {
                *dp = old_pages;
-               if (where[i].count)
+               if (where[i].count || (rw & (1 << BIO_RW_BARRIER)))
                        do_region(rw, i, where + i, dp, io);
        }