Re: [PATCH 1/7] bcachefs: Convert to bdev_open_by_path()

[Brian Foster <bfoster@redhat.com>]

On Thu, Nov 02, 2023 at 10:55:50AM +0100, Jan Kara wrote:
> Hi Brian,
> 
> On Wed 01-11-23 15:01:22, Brian Foster wrote:
> > On Wed, Nov 01, 2023 at 06:43:06PM +0100, Jan Kara wrote:
> > > Convert bcachefs to use bdev_open_by_path() and pass the handle around.
> > > 
> > > CC: Kent Overstreet <kent.overstreet@linux.dev>
> > > CC: Brian Foster <bfoster@redhat.com>
> > > CC: linux-bcachefs@vger.kernel.org
> > > Signed-off-by: Jan Kara <jack@suse.cz>
> > > ---
> > >  fs/bcachefs/super-io.c    | 19 ++++++++++---------
> > >  fs/bcachefs/super_types.h |  1 +
> > >  2 files changed, 11 insertions(+), 9 deletions(-)
> > > 
> > > diff --git a/fs/bcachefs/super-io.c b/fs/bcachefs/super-io.c
> > > index 332d41e1c0a3..01a32c41a540 100644
> > > --- a/fs/bcachefs/super-io.c
> > > +++ b/fs/bcachefs/super-io.c
> > ...
> > > @@ -685,21 +685,22 @@ int bch2_read_super(const char *path, struct bch_opts *opts,
> > >  	if (!opt_get(*opts, nochanges))
> > >  		sb->mode |= BLK_OPEN_WRITE;
> > >  
> > > -	sb->bdev = blkdev_get_by_path(path, sb->mode, sb->holder, &bch2_sb_handle_bdev_ops);
> > > -	if (IS_ERR(sb->bdev) &&
> > > -	    PTR_ERR(sb->bdev) == -EACCES &&
> > > +	sb->bdev_handle = bdev_open_by_path(path, sb->mode, sb->holder, &bch2_sb_handle_bdev_ops);
> > > +	if (IS_ERR(sb->bdev_handle) &&
> > > +	    PTR_ERR(sb->bdev_handle) == -EACCES &&
> > >  	    opt_get(*opts, read_only)) {
> > >  		sb->mode &= ~BLK_OPEN_WRITE;
> > >  
> > > -		sb->bdev = blkdev_get_by_path(path, sb->mode, sb->holder, &bch2_sb_handle_bdev_ops);
> > > -		if (!IS_ERR(sb->bdev))
> > > +		sb->bdev_handle = bdev_open_by_path(path, sb->mode, sb->holder, &bch2_sb_handle_bdev_ops);
> > > +		if (!IS_ERR(sb->bdev_handle))
> > >  			opt_set(*opts, nochanges, true);
> > >  	}
> > >  
> > > -	if (IS_ERR(sb->bdev)) {
> > > -		ret = PTR_ERR(sb->bdev);
> > > +	if (IS_ERR(sb->bdev_handle)) {
> > > +		ret = PTR_ERR(sb->bdev_handle);
> > >  		goto out;
> > >  	}
> > > +	sb->bdev = sb->bdev_handle->bdev;
> > >  
> > >  	ret = bch2_sb_realloc(sb, 0);
> > >  	if (ret) {
> > 
> > This all seems reasonable to me, but should bcachefs use sb_open_mode()
> > somewhere in here to involve use of the restrict writes flag in the
> > first place? It looks like bcachefs sort of open codes bits of
> > mount_bdev() so it isn't clear the flag would be used anywhere...
> 
> Yes, so AFAICS bcachefs will not get the write restriction from the changes
> in the generic code. Using sb_open_mode() in bcachefs would fix that but
> given the 'noexcl' and 'nochanges' mount options it will not be completely
> seamless anyway. I guess once the generic changes are in, bcachefs can
> decide how exactly it wants to set the BLK_OPEN_RESTRICT_WRITES flag. Or if
> you already have an opinion, we can just add the patch to this series.
> 

Yep, makes sense, and I agree with Kent this should be a separate patch
anyways. Just wanted to make sure I wasn't missing something or
otherwise it was known that bcachefs needs a bit more work to turn this
on... thanks.

Brian

> 								Honza
> -- 
> Jan Kara <jack@suse.com>
> SUSE Labs, CR
>