Re: [PATCH 05/17] btrfs: open block devices after superblock creation

[David Sterba <dsterba@suse.cz>]

On Fri, Aug 11, 2023 at 02:44:50PM +0200, Christian Brauner wrote:
> On Fri, Aug 11, 2023 at 12:08:16PM +0200, Christoph Hellwig wrote:
> > Currently btrfs_mount_root opens the block devices before committing to
> > allocating a super block. That creates problems for restricting the
> > number of writers to a device, and also leads to a unusual and not very
> > helpful holder (the fs_type).
> > 
> > Reorganize the code to first check whether the superblock for a
> > particular fsid does already exist and open the block devices only if it
> > doesn't, mirroring the recent changes to the VFS mount helpers.  To do
> > this the increment of the in_use counter moves out of btrfs_open_devices
> > and into the only caller in btrfs_mount_root so that it happens before
> > dropping uuid_mutex around the call to sget.
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > ---
> 
> Looks good to me,
> Acked-by: Christian Brauner <brauner@kernel.org>
> 
> And ofc, would be great to get btrfs reviews.

I'll take a look but there are some performance regressions to deal with
and pre-merge window freeze so it won't be soon.