Re: [PATCH 05/24] fs: Get proper reference for s_bdi

[Jan Kara <jack@suse.cz>]

On Thu 09-02-17 16:36:13, Boaz Harrosh wrote:
> On 02/02/2017 07:34 PM, Jan Kara wrote:
> > 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 <jack@suse.com>
SUSE Labs, CR