Btrfs devel - Oct 2013 - regression, can't mount subvol if default subvol is changed

After changing the default subvolume, I can''t mount a nested subvolume
with a correct relative pathname to the default subvolume; it can only be
mounted by absolute path or subvolid.

Setup: 
3.11.4-302.fc20.x86_64
btrfs-progs-0.20.rc1.20130917git194aa4a-1.fc20.x86_64
dir = a directory, sub=a subvolume, nested=a subvolume; set-default is top level
5


# mount -o subvol=dir/sub /dev/vda1 /mnt
# btrfs subvol list /mnt
ID 263 gen 140 top level 5 path dir/sub
ID 264 gen 140 top level 263 path nested

# btrfs subvol set-default 263 /mnt
# umount /mnt
# mount -o subvol=nested /dev/vda1 /mnt
mount: mount(2) failed: No such file or directory
# mount -o subvol=/nested /dev/vda1 /mnt
mount: mount(2) failed: No such file or directory

# mount -o subvol=/dir/sub/nested /dev/vda1 /mnt
[works]
# umount  /mnt
# mount -o subvolid=264 /dev/vda1 /mnt
[works]


The subvol nested is under dir/sub which is ID 263. So if set-default is 263, I
should be able to mount with subvol=nested as a relative path to the default
subvolume, but it fails. There''s no meaningful kernel message at the
time of the failed mount, just:
[ 4265.386990] device label fedora devid 1 transid 165 /dev/vda1

But I get the exact same message with a successful mount.

So should the mounting of relative pathnames still work?

Chris Murphy--
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On Oct 15, 2013, at 1:23 PM, Chris Murphy <lists@colorremedies.com>
wrote:
> 
> So should the mounting of relative pathnames still work?
Is it related to fix: [PATCH] Btrfs: use right root when checking for hash
collision

can''t move subvols into subvols
http://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg27848.html


Chris Murphy--
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On Oct 15, 2013, at 1:23 PM, Chris Murphy <lists@colorremedies.com> wrote:
> After changing the default subvolume, I can''t mount a nested
subvolume with a correct relative pathname to the default subvolume; it can only
be mounted by absolute path or subvolid.
> 
> Setup: 
> 3.11.4-302.fc20.x86_64
> btrfs-progs-0.20.rc1.20130917git194aa4a-1.fc20.x86_64
> dir = a directory, sub=a subvolume, nested=a subvolume; set-default is top
level 5
> 
> 
> # mount -o subvol=dir/sub /dev/vda1 /mnt
> # btrfs subvol list /mnt
> ID 263 gen 140 top level 5 path dir/sub
> ID 264 gen 140 top level 263 path nested
> 
> # btrfs subvol set-default 263 /mnt
> # umount /mnt
> # mount -o subvol=nested /dev/vda1 /mnt
> mount: mount(2) failed: No such file or directory
> # mount -o subvol=/nested /dev/vda1 /mnt
> mount: mount(2) failed: No such file or directory
> 
> # mount -o subvol=/dir/sub/nested /dev/vda1 /mnt
> [works]
> # umount  /mnt
> # mount -o subvolid=264 /dev/vda1 /mnt
> [works]
> 
Further both of these work and produce the same results

# mount -o subvol=/dir/sub/nested /dev/vda1 /mnt
# mount -o subvol=dir/sub/nested /dev/vda1 /mnt

I think that''s wrong, unless set-default is effectively deprecated. Is
it? /dir/ and dir/ are not the same thing, but even with set-default 263 both of
those work as if they were the same thing.


Chris Murphy--
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On Tue, Oct 15, 2013 at 01:23:44PM -0600, Chris Murphy
wrote:
> After changing the default subvolume, I can''t mount a nested
subvolume
> with a correct relative pathname to the default subvolume; it can only
> be mounted by absolute path or subvolid.
The path to subvol= is always taken as absolute, no matter if the path
starts with / or not.

david
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On Oct 15, 2013, at 2:50 PM, David Sterba <dsterba@suse.cz> wrote:
> On Tue, Oct 15, 2013 at 01:23:44PM -0600, Chris Murphy wrote:
>> After changing the default subvolume, I can''t mount a nested
subvolume
>> with a correct relative pathname to the default subvolume; it can only
>> be mounted by absolute path or subvolid.
> 
> The path to subvol= is always taken as absolute, no matter if the path
> starts with / or not.
Looks like this changed with the 3.2 kernel " Subvolumes mountable by full
path", I thought that was in addition to relative rather than a total
change in behavior. Good to know.

Is the idea that subvolume set-default only affects mount -o defaults behavior
and nothing else?


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On Tue, Oct 15, 2013 at 02:58:22PM -0600, Chris Murphy
wrote:
> Looks like this changed with the 3.2 kernel " Subvolumes mountable by
> full path", I thought that was in addition to relative rather than a
> total change in behavior. Good to know.
Yes, the pre-3.2 behaviour was limited to subvolumes in the toplevel
subvolume, nested subvols were mountable via subvolrootid, but that was
only a clumsy temporary workaround.
> Is the idea that subvolume set-default only affects mount -o defaults
> behavior and nothing else?
Yes.
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On Oct 15, 2013, at 3:48 PM, David Sterba <dsterba@suse.cz> wrote:
> On Tue, Oct 15, 2013 at 02:58:22PM -0600, Chris Murphy wrote:
>> Looks like this changed with the 3.2 kernel " Subvolumes mountable
by
>> full path", I thought that was in addition to relative rather than
a
>> total change in behavior. Good to know.
> 
> Yes, the pre-3.2 behaviour was limited to subvolumes in the toplevel
> subvolume, nested subvols were mountable via subvolrootid, but that was
> only a clumsy temporary workaround.
> 
>> Is the idea that subvolume set-default only affects mount -o defaults
>> behavior and nothing else?
> 
> Yes.
Great, thanks for the clarification.

Chris Murphy
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