Re: [PATCH v3 3/4] fs: make _submit_bh consistent with generic bio chaining

[Christoph Hellwig <hch@infradead.org>]

On Thu, Apr 23, 2015 at 04:04:34PM -0700, Ming Lin wrote:
> From: Kent Overstreet <kent.overstreet@gmail.com>
> 
> Make _submit_bh() handle refcounting by increasing bio->bi_remaining,
> followed by bio_endio(). Since bio chaining was introduced with
> 196d38bccfcf ("block: Generic bio chaining"), refcounting should be
> done on bi_remaining instead of ancient bio_cnt. Doing that, calling
> convention can be consistent with the immutable biovecs API.

I think this and the copy & paste version in nilfs2 can just go away.
Since the big barrier to flush rewrite we will never fail FUA
and FLUSH requests with BIO_EOPNOTSUPP.  That error is just left
for DISCARD adn WRITE_SAME.  So something like the untested patch
below should take care of this:

diff --git a/block/bounce.c b/block/bounce.c
index ab21ba2..4bac725 100644
--- a/block/bounce.c
+++ b/block/bounce.c
@@ -128,9 +128,6 @@ static void bounce_end_io(struct bio *bio, mempool_t *pool, int err)
 	struct bio_vec *bvec, *org_vec;
 	int i;
 
-	if (test_bit(BIO_EOPNOTSUPP, &bio->bi_flags))
-		set_bit(BIO_EOPNOTSUPP, &bio_orig->bi_flags);
-
 	/*
 	 * free up bounce indirect pages used
 	 */
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 639f266..e8d7670 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3225,11 +3225,8 @@ static int write_dev_supers(struct btrfs_device *device,
  */
 static void btrfs_end_empty_barrier(struct bio *bio, int err)
 {
-	if (err) {
-		if (err == -EOPNOTSUPP)
-			set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
+	if (err)
 		clear_bit(BIO_UPTODATE, &bio->bi_flags);
-	}
 	if (bio->bi_private)
 		complete(bio->bi_private);
 	bio_put(bio);
@@ -3257,11 +3254,7 @@ static int write_dev_flush(struct btrfs_device *device, int wait)
 
 		wait_for_completion(&device->flush_wait);
 
-		if (bio_flagged(bio, BIO_EOPNOTSUPP)) {
-			printk_in_rcu("BTRFS: disabling barriers on dev %s\n",
-				      rcu_str_deref(device->name));
-			device->nobarriers = 1;
-		} else if (!bio_flagged(bio, BIO_UPTODATE)) {
+		if (!bio_flagged(bio, BIO_UPTODATE)) {
 			ret = -EIO;
 			btrfs_dev_stat_inc_and_print(device,
 				BTRFS_DEV_STAT_FLUSH_ERRS);
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index d688cfe..6a44bea 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2767,8 +2767,6 @@ static int __must_check submit_one_bio(int rw, struct bio *bio,
 	else
 		btrfsic_submit_bio(rw, bio);
 
-	if (bio_flagged(bio, BIO_EOPNOTSUPP))
-		ret = -EOPNOTSUPP;
 	bio_put(bio);
 	return ret;
 }
diff --git a/fs/buffer.c b/fs/buffer.c
index c7a5602..efd85e0 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2938,10 +2938,6 @@ static void end_bio_bh_io_sync(struct bio *bio, int err)
 {
 	struct buffer_head *bh = bio->bi_private;
 
-	if (err == -EOPNOTSUPP) {
-		set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
-	}
-
 	if (unlikely (test_bit(BIO_QUIET,&bio->bi_flags)))
 		set_bit(BH_Quiet, &bh->b_state);
 
@@ -3041,13 +3037,7 @@ int _submit_bh(int rw, struct buffer_head *bh, unsigned long bio_flags)
 	if (buffer_prio(bh))
 		rw |= REQ_PRIO;
 
-	bio_get(bio);
 	submit_bio(rw, bio);
-
-	if (bio_flagged(bio, BIO_EOPNOTSUPP))
-		ret = -EOPNOTSUPP;
-
-	bio_put(bio);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(_submit_bh);
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 5765f88..c5d81e8 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -359,7 +359,6 @@ void ext4_io_submit(struct ext4_io_submit *io)
 	if (bio) {
 		bio_get(io->io_bio);
 		submit_bio(io->io_op, io->io_bio);
-		BUG_ON(bio_flagged(io->io_bio, BIO_EOPNOTSUPP));
 		bio_put(io->io_bio);
 	}
 	io->io_bio = NULL;
diff --git a/fs/nilfs2/segbuf.c b/fs/nilfs2/segbuf.c
index dc3a9efd..42468e5 100644
--- a/fs/nilfs2/segbuf.c
+++ b/fs/nilfs2/segbuf.c
@@ -343,11 +343,6 @@ static void nilfs_end_bio_write(struct bio *bio, int err)
 	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
 	struct nilfs_segment_buffer *segbuf = bio->bi_private;
 
-	if (err == -EOPNOTSUPP) {
-		set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
-		/* to be detected by nilfs_segbuf_submit_bio() */
-	}
-
 	if (!uptodate)
 		atomic_inc(&segbuf->sb_err);
 
@@ -374,15 +369,8 @@ static int nilfs_segbuf_submit_bio(struct nilfs_segment_buffer *segbuf,
 
 	bio->bi_end_io = nilfs_end_bio_write;
 	bio->bi_private = segbuf;
-	bio_get(bio);
 	submit_bio(mode, bio);
 	segbuf->sb_nbio++;
-	if (bio_flagged(bio, BIO_EOPNOTSUPP)) {
-		bio_put(bio);
-		err = -EOPNOTSUPP;
-		goto failed;
-	}
-	bio_put(bio);
 
 	wi->bio = NULL;
 	wi->rest_blocks -= wi->end - wi->start;
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index a1b25e3..809feb3 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -118,7 +118,6 @@ struct bio {
 #define BIO_CLONED	4	/* doesn't own data */
 #define BIO_BOUNCED	5	/* bio is a bounce bio */
 #define BIO_USER_MAPPED 6	/* contains user pages */
-#define BIO_EOPNOTSUPP	7	/* not supported */
 #define BIO_NULL_MAPPED 8	/* contains invalid user pages */
 #define BIO_QUIET	9	/* Make BIO Quiet */
 #define BIO_SNAP_STABLE	10	/* bio data must be snapshotted during write */