linux-kernel - Re: [PATCH v2 2/6] Btrfs: remove all subvol options before mounting top-level

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Message-ID: <20150511160824.GQ23255@twin.jikos.cz>
Date:	Mon, 11 May 2015 18:08:24 +0200
From:	David Sterba <dsterba@...e.cz>
To:	Omar Sandoval <osandov@...ndov.com>
Cc:	Chris Mason <clm@...com>, Josef Bacik <jbacik@...com>,
	David Sterba <dsterba@...e.cz>, linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, Qu Wenruo <quwenruo@...fujitsu.com>
Subject: Re: [PATCH v2 2/6] Btrfs: remove all subvol options before mounting
 top-level

On Thu, Apr 09, 2015 at 02:34:52PM -0700, Omar Sandoval wrote:
> Currently, setup_root_args() substitutes 's/subvol=[^,]*/subvolid=0/'.
> But, this means that if the user passes both a subvol and subvolid for
> some reason, we won't actually mount the top-level when we recursively
> mount. For example, consider:
> 
> mkfs.btrfs -f /dev/sdb
> mount /dev/sdb /mnt
> btrfs subvol create /mnt/subvol1 # subvolid=257
> btrfs subvol create /mnt/subvol2 # subvolid=258
> umount /mnt
> mount -osubvol=/subvol1,subvolid=258 /dev/sdb /mnt
> 
> In the final mount, subvol=/subvol1,subvolid=258 becomes
> subvolid=0,subvolid=258, and the last option takes precedence, so we
> mount subvol2 and try to look up subvol1 inside of it, which fails.
> 
> So, instead, do a thorough scan through the argument list and remove any
> subvol= and subvolid= options, then append subvolid=0 to the end. This
> implicitly makes subvol= take precedence over subvolid=, but we're about
> to add a stricter check for that. This also makes setup_root_args() more
> generic, which we'll need soon.
> 
> Signed-off-by: Omar Sandoval <osandov@...ndov.com>

Reviewed-by: David Sterba <dsterba@...e.cz>
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