dm: implement REQ_FLUSH/FUA support for bio-based dm

This patch converts bio-based dm to support REQ_FLUSH/FUA instead of
now deprecated REQ_HARDBARRIER.

* -EOPNOTSUPP handling logic dropped.

* Preflush is handled as before but postflush is dropped and replaced
  with passing down REQ_FUA to member request_queues.  This replaces
  one array wide cache flush w/ member specific FUA writes.

* __split_and_process_bio() now calls __clone_and_map_flush() directly
  for flushes and guarantees all FLUSH bio's going to targets are zero
`  length.

* It's now guaranteed that all FLUSH bio's which are passed onto dm
  targets are zero length.  bio_empty_barrier() tests are replaced
  with REQ_FLUSH tests.

* Empty WRITE_BARRIERs are replaced with WRITE_FLUSHes.

* Dropped unlikely() around REQ_FLUSH tests.  Flushes are not unlikely
  enough to be marked with unlikely().

* Block layer now filters out REQ_FLUSH/FUA bio's if the request_queue
  doesn't support cache flushing.  Advertise REQ_FLUSH | REQ_FUA
  capability.

* Request based dm isn't converted yet.  dm_init_request_based_queue()
  resets flush support to 0 for now.  To avoid disturbing request
  based dm code, dm->flush_error is added for bio based dm while
  requested based dm continues to use dm->barrier_error.

Lightly tested linear, stripe, raid1, snap and crypt targets.  Please
proceed with caution as I'm not familiar with the code base.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: dm-devel@redhat.com
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 4 insertions, 16 deletions

diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index 0590c75b0ab6..136d4f71a116 100644
--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -31,7 +31,6 @@ struct dm_io_client {
  */
 struct io {
         unsigned long error_bits;
-        unsigned long eopnotsupp_bits;
         atomic_t count;
         struct task_struct *sleeper;
         struct dm_io_client *client;
@@ -130,11 +129,8 @@ static void retrieve_io_and_region_from_bio(struct bio *bio, struct io **io,
  *---------------------------------------------------------------*/
 static void dec_count(struct io *io, unsigned int region, int error)
 {
-        if (error) {
+        if (error)
                 set_bit(region, &io->error_bits);
-                if (error == -EOPNOTSUPP)
-                        set_bit(region, &io->eopnotsupp_bits);
-        }
 
         if (atomic_dec_and_test(&io->count)) {
                 if (io->sleeper)
@@ -310,8 +306,8 @@ static void do_region(int rw, unsigned region, struct dm_io_region *where,
         sector_t remaining = where->count;
 
         /*
-         * where->count may be zero if rw holds a write barrier and we
-         * need to send a zero-sized barrier.
+         * where->count may be zero if rw holds a flush and we need to
+         * send a zero-sized flush.
          */
         do {
                 /*
@@ -364,7 +360,7 @@ static void dispatch_io(int rw, unsigned int num_regions,
          */
         for (i = 0; i < num_regions; i++) {
                 *dp = old_pages;
-                if (where[i].count || (rw & REQ_HARDBARRIER))
+                if (where[i].count || (rw & REQ_FLUSH))
                         do_region(rw, i, where + i, dp, io);
         }
 
@@ -393,9 +389,7 @@ static int sync_io(struct dm_io_client *client, unsigned int num_regions,
                 return -EIO;
         }
 
-retry:
         io->error_bits = 0;
-        io->eopnotsupp_bits = 0;
         atomic_set(&io->count, 1); /* see dispatch_io() */
         io->sleeper = current;
         io->client = client;
@@ -412,11 +406,6 @@ retry:
         }
         set_current_state(TASK_RUNNING);
 
-        if (io->eopnotsupp_bits && (rw & REQ_HARDBARRIER)) {
-                rw &= ~REQ_HARDBARRIER;
-                goto retry;
-        }
-
         if (error_bits)
                 *error_bits = io->error_bits;
 
@@ -437,7 +426,6 @@ static int async_io(struct dm_io_client *client, unsigned int num_regions,
 
         io = mempool_alloc(client->pool, GFP_NOIO);
         io->error_bits = 0;
-        io->eopnotsupp_bits = 0;
         atomic_set(&io->count, 1); /* see dispatch_io() */
         io->sleeper = NULL;
         io->client = client;