On Tue, 2008-08-12 at 12:54 +0200, Jens Axboe wrote:
> The easy fix is would just be to
> change init_request_from_bio() to do something ala:
>
> if (bio_barrier(bio)) {
> if (bio_has_data(bio))
> req->cmd_flags |= REQ_HARDBARRIER;
> else
> req->cmd_flags |= REQ_SOFTBARRIER;
> }
>
> since there's no real data dependency when you don't have data
> attached.
There's a check in __make_request() which will return -EOPNOTSUPP for
bios with BIO_RW_BARRIER set, in some circumstances. Is that OK too?
I was thinking of using the READ/WRITE bit for it -- just
(1<<BIO_RW_DISCARD) (i.e. read) would imply a barrier, while
having the WRITE bit also set would mean no barrier, and it gets
scheduled like a normal write.
Something like...
diff --git a/block/blk-barrier.c b/block/blk-barrier.c
index e544813..988b634 100644
--- a/block/blk-barrier.c
+++ b/block/blk-barrier.c
@@ -372,7 +372,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
nr_sects = 0;
}
bio_get(bio);
- submit_bio(WRITE_DISCARD, bio);
+ submit_bio(DISCARD_BARRIER, bio);
/* Check if it failed immediately */
if (bio_flagged(bio, BIO_EOPNOTSUPP))
diff --git a/block/blk-core.c b/block/blk-core.c
index 0c8ed97..be2fe52 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1079,6 +1079,13 @@ void init_request_from_bio(struct request *req, struct bio *bio)
req->cmd_flags |= (REQ_HARDBARRIER | REQ_NOMERGE);
if (unlikely(bio_discard(bio))) {
req->cmd_flags |= REQ_DISCARD;
+ /*
+ * READ discard requests are soft barriers; WRITE
+ * indicates the file system will take care of that
+ * for itself.
+ */
+ if (!bio_data_dir(bio))
+ req->cmd_flags |= REQ_SOFTBARRIER;
req->q->prepare_discard_fn(req->q, req);
}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 88358ca..5cfacb3 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -87,7 +87,8 @@ extern int dir_notify_enable;
#define WRITE_SYNC (WRITE | (1 << BIO_RW_SYNC))
#define SWRITE_SYNC (SWRITE | (1 << BIO_RW_SYNC))
#define WRITE_BARRIER (WRITE | (1 << BIO_RW_BARRIER))
-#define WRITE_DISCARD (WRITE | (1 << BIO_RW_DISCARD))
+#define DISCARD_NOBARRIER (WRITE | (1 << BIO_RW_DISCARD))
+#define DISCARD_BARRIER (1 << BIO_RW_DISCARD)
#define SEL_IN 1
#define SEL_OUT 2
--
David Woodhouse Open Source Technology Centre
David.Woodhouse@xxxxxxxxx Intel Corporation
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