read-only subvolumes?

read-only subvolumes?

[Andreas Philipp]

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Hi all,

When I am creating subvolumes I get this strange behavior. If I create
a subvolume with a name longer than 4 characters it is read-only, if
the name is shorter than 5 characters the subvolume is writeable as
expected. I think it is since I upgraded to kernel version 2.6.38 (I
do not create subvolumes on a regular basis.). I will compile one of
the latest 2.6.37 kernels to see whether there the problem exists,
too. Another interesting point is that previously created subvolumes
are not affected.

Thanks,
Andreas Philipp

thor btrfs # btrfs subvolume create 123456789
Create subvolume './123456789'
thor btrfs # touch 123456789/lsdkfj
touch: cannot touch `123456789/lsdkfj': Read-only file system

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Re: read-only subvolumes?

[Fajar A. Nugraha]

On Wed, Mar 23, 2011 at 3:21 PM, Andreas Philipp
<philipp.andreas@gmail.com> wrote:
> I think it is since I upgraded to kernel version 2.6.38 (I
> do not create subvolumes on a regular basis.).

> thor btrfs # btrfs subvolume create 123456789
> Create subvolume './123456789'
> thor btrfs # touch 123456789/lsdkfj
> touch: cannot touch `123456789/lsdkfj': Read-only file system

It works on my system

# touch test1
# btrfs su cr 123456789
Create subvolume './123456789'
# touch 123456789/lsdkfj
# uname -a
Linux HP 2.6.38-020638-generic #201103151303 SMP Tue Mar 15 14:33:40
UTC 2011 i686 GNU/Linux

-- 
Fajar

Re: read-only subvolumes?

[Li Zefan]

> Hi all,
> 
> When I am creating subvolumes I get this strange behavior. If I create
> a subvolume with a name longer than 4 characters it is read-only, if
> the name is shorter than 5 characters the subvolume is writeable as
> expected. I think it is since I upgraded to kernel version 2.6.38 (I
> do not create subvolumes on a regular basis.). I will compile one of
> the latest 2.6.37 kernels to see whether there the problem exists,
> too. Another interesting point is that previously created subvolumes
> are not affected.
> 
> Thanks,
> Andreas Philipp
> 
> thor btrfs # btrfs subvolume create 123456789
> Create subvolume './123456789'
> thor btrfs # touch 123456789/lsdkfj
> touch: cannot touch `123456789/lsdkfj': Read-only file system

This is really odd, but I can't reproduce it.

I created a btrfs filesystem on 2.6.37 kernel, and rebooted to latest
2.6.38+, and tried the procedures as you did, but nothing bad happend.

Re: read-only subvolumes?

[Andreas Philipp]

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Hash: SHA1
 
On 23.03.2011 10:25, Li Zefan wrote:
>> Hi all,
>>
>> When I am creating subvolumes I get this strange behavior. If I
>> create a subvolume with a name longer than 4 characters it is
>> read-only, if the name is shorter than 5 characters the subvolume
>> is writeable as expected. I think it is since I upgraded to
>> kernel version 2.6.38 (I do not create subvolumes on a regular
>> basis.). I will compile one of the latest 2.6.37 kernels to see
>> whether there the problem exists, too. Another interesting point
>> is that previously created subvolumes are not affected.
>>
>> Thanks, Andreas Philipp
>>
>> thor btrfs # btrfs subvolume create 123456789 Create subvolume
>> './123456789' thor btrfs # touch 123456789/lsdkfj touch: cannot
>> touch `123456789/lsdkfj': Read-only file system
>
> This is really odd, but I can't reproduce it.
>
> I created a btrfs filesystem on 2.6.37 kernel, and rebooted to
> latest 2.6.38+, and tried the procedures as you did, but nothing
> bad happend.
While playing around I found the following three new points:
- - Now the length of the subvolume name does not matter. So even the
ones with short names are read-only.
- - It also happens to a fresh newly created btrfs filesystem.
- - If I take a snapshot of an "old" (= writeable) subvolume this is
writeable.

I will now reboot into 2.6.37.4, check there, and then report back.

Thanks,
Andreas Philipp
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Re: read-only subvolumes?

[Andreas Philipp]

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Hash: SHA1
 
On 23.03.2011 11:07, Andreas Philipp wrote:
>
> On 23.03.2011 10:25, Li Zefan wrote:
>>> Hi all,
>>>
>>> When I am creating subvolumes I get this strange behavior. If I
>>> create a subvolume with a name longer than 4 characters it is
>>> read-only, if the name is shorter than 5 characters the
>>> subvolume is writeable as expected. I think it is since I
>>> upgraded to kernel version 2.6.38 (I do not create subvolumes
>>> on a regular basis.). I will compile one of the latest 2.6.37
>>> kernels to see whether there the problem exists, too. Another
>>> interesting point is that previously created subvolumes are
>>> not affected.
>>>
>>> Thanks, Andreas Philipp
>>>
>>> thor btrfs # btrfs subvolume create 123456789 Create subvolume
>>> './123456789' thor btrfs # touch 123456789/lsdkfj touch:
>>> cannot touch `123456789/lsdkfj': Read-only file system
>
>> This is really odd, but I can't reproduce it.
>
>> I created a btrfs filesystem on 2.6.37 kernel, and rebooted to
>> latest 2.6.38+, and tried the procedures as you did, but nothing
>> bad happend.
> While playing around I found the following three new points: - Now
> the length of the subvolume name does not matter. So even the ones
> with short names are read-only. - It also happens to a fresh newly
> created btrfs filesystem. - If I take a snapshot of an "old" (=
> writeable) subvolume this is writeable.
>
> I will now reboot into 2.6.37.4, check there, and then report
> back.

Well, this was fast. Everything works as expected on 2.6.37.4. See the
output of uname -a for the exact kernel version below.
I will now reboot into a differently configured kernel version 2.6.38
and look whether the problem is gone there.

Thanks,
Andreas Philipp

thor ~ # uname -a
Linux thor 2.6.37.4 #2 SMP Wed Mar 23 10:25:54 CET 2011 x86_64
Intel(R) Core(TM)2 CPU 6600 @ 2.40GHz GenuineIntel GNU/Linux
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Re: read-only subvolumes?

[Li Zefan]

>>>>> When I am creating subvolumes I get this strange behavior. If
>>>>> I create a subvolume with a name longer than 4 characters it
>>>>> is read-only, if the name is shorter than 5 characters the
>>>>> subvolume is writeable as expected. I think it is since I
>>>>> upgraded to kernel version 2.6.38 (I do not create
>>>>> subvolumes on a regular basis.). I will compile one of the
>>>>> latest 2.6.37 kernels to see whether there the problem
>>>>> exists, too. Another interesting point is that previously
>>>>> created subvolumes are not affected.
>>>>>
>>>>> Thanks, Andreas Philipp
>>>>>
>>>>> thor btrfs # btrfs subvolume create 123456789 Create
>>>>> subvolume './123456789' thor btrfs # touch 123456789/lsdkfj
>>>>> touch: cannot touch `123456789/lsdkfj': Read-only file
>>>>> system
>>
>>>> This is really odd, but I can't reproduce it.
>>
>>>> I created a btrfs filesystem on 2.6.37 kernel, and rebooted to
>>>> latest 2.6.38+, and tried the procedures as you did, but
>>>> nothing bad happend.
>>> While playing around I found the following three new points: -
>>> Now the length of the subvolume name does not matter. So even the
>>> ones with short names are read-only. - It also happens to a fresh
>>> newly created btrfs filesystem. - If I take a snapshot of an
>>> "old" (= writeable) subvolume this is writeable.
>>
>>> I will now reboot into 2.6.37.4, check there, and then report
>>> back.
>>
>> Well, this was fast. Everything works as expected on 2.6.37.4. See
>> the output of uname -a for the exact kernel version below. I will
>> now reboot into a differently configured kernel version 2.6.38 and
>> look whether the problem is gone there.
>>
>> Thanks, Andreas Philipp
>>
>> thor ~ # uname -a Linux thor 2.6.37.4 #2 SMP Wed Mar 23 10:25:54
>> CET 2011 x86_64 Intel(R) Core(TM)2 CPU 6600 @ 2.40GHz GenuineIntel
>> GNU/Linux
> 
> IMHO, this is related to how the debug options of the kernel are
> configured. Attached you find two config files, both for kernel
> version 2.6.38, with the one named 2.6.38-debug everything works and
> with the other one newly created subvolumes are read only.
> 

I'll see if I can reproduce the problem using your config. Thanks!

Re: read-only subvolumes?

[Li Zefan]

> IMHO, this is related to how the debug options of the kernel are
> configured. Attached you find two config files, both for kernel
> version 2.6.38, with the one named 2.6.38-debug everything works and
> with the other one newly created subvolumes are read only.
> 

I've figured out what's wrong.

The root cause is the flags field of the root item for a new subvol
is never _initialized_!! so the on disk root_item->flags can be of
arbitrary value..

(so is root_item->byte_limit btw.)

I don't have a perfect solution at the moment, but I think a workaround
is to use a flag in root_item->inode_item->flags to indicate if
root->flags is initialized.