Correct bioq_disksort so that bioq_insert_tail() offers barrier semantic.

Add the BIO_ORDERED flag for struct bio and update bio clients to use it.

The barrier semantics of bioq_insert_tail() were broken in two ways:

 o In bioq_disksort(), an added bio could be inserted at the head of
   the queue, even when a barrier was present, if the sort key for
   the new entry was less than that of the last queued barrier bio.

 o The last_offset used to generate the sort key for newly queued bios
   did not stay at the position of the barrier until either the
   barrier was de-queued, or a new barrier (which updates last_offset)
   was queued.  When a barrier is in effect, we know that the disk
   will pass through the barrier position just before the
   "blocked bios" are released, so using the barrier's offset for
   last_offset is the optimal choice.

sys/geom/sched/subr_disk.c:
sys/kern/subr_disk.c:
	o Update last_offset in bioq_insert_tail().

	o Only update last_offset in bioq_remove() if the removed bio is
	  at the head of the queue (typically due to a call via
	  bioq_takefirst()) and no barrier is active.

	o In bioq_disksort(), if we have a barrier (insert_point is non-NULL),
	  set prev to the barrier and cur to it's next element.  Now that
	  last_offset is kept at the barrier position, this change isn't
	  strictly necessary, but since we have to take a decision branch
	  anyway, it does avoid one, no-op, loop iteration in the while
	  loop that immediately follows.

	o In bioq_disksort(), bypass the normal sort for bios with the
	  BIO_ORDERED attribute and instead insert them into the queue
	  with bioq_insert_tail().  bioq_insert_tail() not only gives
	  the desired command order during insertion, but also provides
	  barrier semantics so that commands disksorted in the future
	  cannot pass the just enqueued transaction.

sys/sys/bio.h:
	Add BIO_ORDERED as bit 4 of the bio_flags field in struct bio.

sys/cam/ata/ata_da.c:
sys/cam/scsi/scsi_da.c
	Use an ordered command for SCSI/ATA-NCQ commands issued in
	response to bios with the BIO_ORDERED flag set.

sys/cam/scsi/scsi_da.c
	Use an ordered tag when issuing a synchronize cache command.

	Wrap some lines to 80 columns.

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c
sys/geom/geom_io.c
	Mark bios with the BIO_FLUSH command as BIO_ORDERED.

Sponsored by:	Spectra Logic Corporation
MFC after:	1 month

1 files changed, 1 insertions, 0 deletions

diff --git a/sys/geom/geom_io.c b/sys/geom/geom_io.c
index b145441..b4044a7 100644
--- a/sys/geom/geom_io.c
+++ b/sys/geom/geom_io.c
@@ -265,6 +265,7 @@ g_io_flush(struct g_consumer *cp)
 	g_trace(G_T_BIO, "bio_flush(%s)", cp->provider->name);
 	bp = g_alloc_bio();
 	bp->bio_cmd = BIO_FLUSH;
+	bp->bio_flags |= BIO_ORDERED;
 	bp->bio_done = NULL;
 	bp->bio_attribute = NULL;
 	bp->bio_offset = cp->provider->mediasize;