linux-kernel - Re: [PATCH v2 5/6] Btrfs: unify subvol= and subvolid= mounting

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Message-ID: <20150511211531.GA10078@mew.dhcp4.washington.edu>
Date:	Mon, 11 May 2015 14:15:31 -0700
From:	Omar Sandoval <osandov@...ndov.com>
To:	dsterba@...e.cz, Chris Mason <clm@...com>,
	Josef Bacik <jbacik@...com>, linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, Qu Wenruo <quwenruo@...fujitsu.com>
Subject: Re: [PATCH v2 5/6] Btrfs: unify subvol= and subvolid= mounting

On Mon, May 11, 2015 at 05:37:24PM +0200, David Sterba wrote:
> On Thu, Apr 09, 2015 at 02:34:55PM -0700, Omar Sandoval wrote:
> > @@ -1321,7 +1438,7 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
> >  		return ERR_PTR(error);
> >  	}
> >  
> > -	if (subvol_name) {
> > +	if (subvol_name || subvol_objectid != BTRFS_FS_TREE_OBJECTID) {
> >  		/* mount_subvol() will free subvol_name. */
> >  		return mount_subvol(subvol_name, subvol_objectid, flags,
> >  				    device_name, data);
> 
> The story is that I've used this patchset as a base for my per-subvolume
> mount flags because it made the mount path cleaner, so it's possible that
> the issue I saw was related to my changes.
> 
> The modified 'if' above did not catch subvol_objectid == 0. I'm not sure
> now how it got there, btrfs_parse_early_options recognizes 0 and
> switches it to 5.
> 
> My testing script is quite simple and does only
> 
>   mount -o compress-force=lzo,subvol=/subv1 $dev mnt
>   mount -o compress-force=zlib,subvol=/subv2 $dev mnt2
> 
> after mkfs. The first pass would resolve the path to the subvol root and
> replace the options with subvolid=0, calls mount_subvol, vfs_kern_mount
> than in turn goes back to btrfs_mount. Unless I'm missing something,
> this should also work, because parse_early_options is called again and
> does subvolid=0 -> subvol_objectid=5 . Oh well, more debugging needed,
> not a blocker for this patchset.

Hm, yeah, I don't see how that would happen. Do you have that patchset
up anywhere?

-- 
Omar
--
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