[PATCH] dm: mpath: use noflush suspending

Implement the pushback feature for the multipath target.

The pushback request is used when:
  1) there are no valid paths;
  2) queue_if_no_path was set;
  3) a suspend is being issued with the DMF_NOFLUSH_SUSPENDING flag.
     Otherwise bios are returned to applications with -EIO.

To check whether queue_if_no_path is specified or not, you need to check
both queue_if_no_path and saved_queue_if_no_path, because presuspend saves
the original queue_if_no_path value to saved_queue_if_no_path.

The check for 1 already exists in both map_io() and do_end_io().
So this patch adds __must_push_back() to check 2 and 3.

Test results:
See the test results in the preceding patch.

Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Cc: dm-devel@redhat.com
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 29 insertions, 5 deletions

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index d325edcbb3f5..3aa013506967 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -282,6 +282,23 @@ failed:
         m->current_pg = NULL;
 }
 
+/*
+ * Check whether bios must be queued in the device-mapper core rather
+ * than here in the target.
+ *
+ * m->lock must be held on entry.
+ *
+ * If m->queue_if_no_path and m->saved_queue_if_no_path hold the
+ * same value then we are not between multipath_presuspend()
+ * and multipath_resume() calls and we have no need to check
+ * for the DMF_NOFLUSH_SUSPENDING flag.
+ */
+static int __must_push_back(struct multipath *m)
+{
+        return (m->queue_if_no_path != m->saved_queue_if_no_path &&
+                dm_noflush_suspending(m->ti));
+}
+
 static int map_io(struct multipath *m, struct bio *bio, struct mpath_io *mpio,
                   unsigned was_queued)
 {
@@ -311,10 +328,12 @@ static int map_io(struct multipath *m, struct bio *bio, struct mpath_io *mpio,
                         queue_work(kmultipathd, &m->process_queued_ios);
                 pgpath = NULL;
                 r = DM_MAPIO_SUBMITTED;
-        } else if (!pgpath)
-                r = -EIO;               /* Failed */
-        else
+        } else if (pgpath)
                 bio->bi_bdev = pgpath->path.dev->bdev;
+        else if (__must_push_back(m))
+                r = DM_MAPIO_REQUEUE;
+        else
+                r = -EIO;       /* Failed */
 
         mpio->pgpath = pgpath;
 
@@ -374,6 +393,8 @@ static void dispatch_queued_ios(struct multipath *m)
                         bio_endio(bio, bio->bi_size, r);
                 else if (r == DM_MAPIO_REMAPPED)
                         generic_make_request(bio);
+                else if (r == DM_MAPIO_REQUEUE)
+                        bio_endio(bio, bio->bi_size, -EIO);
 
                 bio = next;
         }
@@ -783,7 +804,7 @@ static int multipath_map(struct dm_target *ti, struct bio *bio,
         map_context->ptr = mpio;
         bio->bi_rw |= (1 << BIO_RW_FAILFAST);
         r = map_io(m, bio, mpio, 0);
-        if (r < 0)
+        if (r < 0 || r == DM_MAPIO_REQUEUE)
                 mempool_free(mpio, m->mpio_pool);
 
         return r;
@@ -1007,7 +1028,10 @@ static int do_end_io(struct multipath *m, struct bio *bio,
 
         spin_lock_irqsave(&m->lock, flags);
         if (!m->nr_valid_paths) {
-                if (!m->queue_if_no_path) {
+                if (__must_push_back(m)) {
+                        spin_unlock_irqrestore(&m->lock, flags);
+                        return DM_ENDIO_REQUEUE;
+                } else if (!m->queue_if_no_path) {
                         spin_unlock_irqrestore(&m->lock, flags);
                         return -EIO;
                 } else {