On Thu 09-02-17 16:36:13, Boaz Harrosh wrote:

On 02/02/2017 07:34 PM, Jan Kara wrote:

quoted

So far we just relied on block device to hold a bdi reference for us
while the filesystem is mounted. While that works perfectly fine, it is
a bit awkward that we have a pointer to a refcounted structure in the
superblock without proper reference. So make s_bdi hold a proper
reference to block device's BDI. No filesystem using mount_bdev()
actually changes s_bdi so this is safe and will make bdev filesystems
work the same way as filesystems needing to set up their private bdi.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/super.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index 31dc4c6450ef..dfb95ccd4351 100644
--- a/fs/super.c
+++ b/fs/super.c

@@ -1047,12 +1047,9 @@ static int set_bdev_super(struct super_block *s, void *data)
 {
 	s->s_bdev = data;
 	s->s_dev = s->s_bdev->bd_dev;
+	s->s_bdi = bdi_get(s->s_bdev->bd_bdi);
+	s->s_iflags |= SB_I_DYNBDI;
 
-	/*
-	 * We set the bdi here to the queue backing, file systems can
-	 * overwrite this in ->fill_super()
-	 */

Question: So I have an FS that uses mount_bdev but than goes and
overrides sb->s_bdev in ->fill_super() anyway. This is because of two
reasons. One because I have many more devices. (like btrfs I'm
moulti-dev) but I like to use mount_bdev because of the somewhat delicate
handling of automatic bind-mounts.

For me it is a bigger hack to get the ref-counting and bind-mounts
locking correctly then to bdi_put and say the new super_setup_bdi(sb) in
fill_super. Would you expect problems?

No, that should work just fine.
	
								Honza
-- 
Jan Kara [off-list ref]
SUSE Labs, CR