[PATCH 6/7] btrfs_get_dev_args_from_path(): don't call set_blocksize()

[Al Viro <viro@zeniv.linux.org.uk>]

We don't have bdev opened exclusive there.  And I'm rather dubious
about the need to do set_blocksize() anywhere in btrfs, to be
honest - there's some access to page cache of underlying block
devices in there, but it's nowhere near the hot paths, AFAICT.

In any case, btrfs_get_dev_args_from_path() only needs to read
the on-disk superblock and copy several fields out of it; all
callers are only interested in devices that are already opened
and brought into per-filesystem set, so setting the block size
is redundant for those and actively harmful if we are given
a pathname of unrelated device.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/btrfs/volumes.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index f15591f3e54f..43af5a9fb547 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -482,10 +482,12 @@ btrfs_get_bdev_and_sb(const char *device_path, blk_mode_t flags, void *holder,
 
 	if (flush)
 		sync_blockdev(bdev);
-	ret = set_blocksize(bdev, BTRFS_BDEV_BLOCKSIZE);
-	if (ret) {
-		fput(*bdev_file);
-		goto error;
+	if (holder) {
+		ret = set_blocksize(bdev, BTRFS_BDEV_BLOCKSIZE);
+		if (ret) {
+			fput(*bdev_file);
+			goto error;
+		}
 	}
 	invalidate_bdev(bdev);
 	*disk_super = btrfs_read_dev_super(bdev);
@@ -498,6 +500,7 @@ btrfs_get_bdev_and_sb(const char *device_path, blk_mode_t flags, void *holder,
 	return 0;
 
 error:
+	*disk_super = NULL;
 	*bdev_file = NULL;
 	return ret;
 }
-- 
2.39.2