Hi,
I'm adding cache flush support to the PS3 disk driver and have a few questions
related to barriers.
In my driver, I do:
blk_queue_issue_flush_fn(queue, ps3disk_issue_flush);
blk_queue_ordered(queue, QUEUE_ORDERED_DRAIN_FLUSH, ps3disk_prepare_flush);
but I can't find a way to actually trigger the calling of ps3disk_issue_flush()
and ps3disk_prepare_flush().
1. My prepare_flush_fn() routine should be called from queue_flush(), which is
in turn called by start_ordered().
start_ordered() is called by blk_do_ordered(), but only if there's no
barrier (REQ_HARDBARRIER is not set).
Apart from drivers/block/pktcdvd.c and init_request_from_bio()
(BIO_RW_BARRIER is set by drivers/md/md.c only?), the only other way
REQ_HARDBARRIER can be set is in queue_flush(), which is not possible.
2. My issue_flush_fn() should be called from blkdev_issue_flush() (ignoring
drivers/md). But blkdev_issue_flush() is called by ReiserFS and XFS only.
I read the Block Device chapter in Linux Device Drivers 3rd edition, which says
to check blk_barrier_rq(), but the barrier part seems to be obsolete, as we now
have the prepare_flush_fn parameter of blk_queue_ordered().
Am I missing something? Should I care about barriers?
Thanks!
BTW, Documentation/block/barrier.txt seems to be out-of-date. Patch to update
it is below.
---
Documentation/block/barrier.txt is not in sync with the actual code:
- blk_queue_ordered() no longer has a gfp_mask parameter
- blk_queue_ordered_locked() no longer exists
- sd_prepare_flush() looks slightly different
Signed-off-by: Geert Uytterhoeven <[email protected]>
--- a/Documentation/block/barrier.txt
+++ b/Documentation/block/barrier.txt
@@ -82,23 +82,12 @@ including draining and flushing.
typedef void (prepare_flush_fn)(request_queue_t *q, struct request *rq);
int blk_queue_ordered(request_queue_t *q, unsigned ordered,
- prepare_flush_fn *prepare_flush_fn,
- unsigned gfp_mask);
-
-int blk_queue_ordered_locked(request_queue_t *q, unsigned ordered,
- prepare_flush_fn *prepare_flush_fn,
- unsigned gfp_mask);
-
-The only difference between the two functions is whether or not the
-caller is holding q->queue_lock on entry. The latter expects the
-caller is holding the lock.
+ prepare_flush_fn *prepare_flush_fn);
@q : the queue in question
@ordered : the ordered mode the driver/device supports
@prepare_flush_fn : this function should prepare @rq such that it
flushes cache to physical medium when executed
-@gfp_mask : gfp_mask used when allocating data structures
- for ordered processing
For example, SCSI disk driver's prepare_flush_fn looks like the
following.
@@ -106,9 +95,10 @@ following.
static void sd_prepare_flush(request_queue_t *q, struct request *rq)
{
memset(rq->cmd, 0, sizeof(rq->cmd));
- rq->flags |= REQ_BLOCK_PC;
+ rq->cmd_type = REQ_TYPE_BLOCK_PC;
rq->timeout = SD_TIMEOUT;
rq->cmd[0] = SYNCHRONIZE_CACHE;
+ rq->cmd_len = 10;
}
The following seven ordered modes are supported. The following table
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- Sony Network and Software Technology Center Europe (NSCE)
[email protected] ------- The Corporate Village, Da Vincilaan 7-D1
Voice +32-2-7008453 Fax +32-2-7008622 ---------------- B-1935 Zaventem, Belgium
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