Re: Can't mount subvolume with ro option

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

-------- Original Message --------
Subject: Re: Can't mount subvolume with ro option
From: Sébastien ROHAUT <sebastien.rohaut@free.fr>
To: Chris Murphy <lists@colorremedies.com>
Date: 2014年06月28日 19:02
> Le 28/06/2014 00:12, Chris Murphy a écrit :
>> On Jun 27, 2014, at 4:08 PM, Chris Murphy <lists@colorremedies.com> 
>> wrote:
>>
>>> On Jun 27, 2014, at 2:07 PM, Sébastien ROHAUT 
>>> <sebastien.rohaut@free.fr> wrote:
>>>
>>>> Hi,
>>>>
>>>> In the wiki, it's said we can mount subvolumes with different mount 
>>>> options. nosuid, nodev, rw and ro are listed, as valid generic 
>>>> mount options.
>>> This might require 3.15. I don't recall it working with early 3.14 
>>> kernels, but by 3.14.3 I'd moved onto testing 3.15.
>>
>> [root@f20v ~]# mount /dev/sda3 /mnt
>> [root@f20v ~]# btrfs subvol create /mnt/test
>> Create subvolume '/mnt/test'
>> [root@f20v ~]# umount /mnt
>> [root@f20v ~]# mount -o ro,subvol=test /dev/sda3 /mnt
>> mount: /dev/sda3 is already mounted or /mnt busy
>>         /dev/sda3 is already mounted on /
>>         /dev/sda3 is already mounted on /home
>>         /dev/sda3 is already mounted on /var
>>         /dev/sda3 is already mounted on /boot
>> [root@f20v ~]# uname -r
>> 3.14.6-200.fc20.x86_64
>>
>>
>> I don't know if this feature will be backported to stable kernels. If 
>> not, then probably the wiki should say it's a 3.15+ feature.
>> Chris Murphy
>>
>>
> Thank you for your answer. I'm actually moving to a Fedora Rawhide 
> (3.16 kernel).
>
> Sebastien Rohaut
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When testing on 3.15.2-ARCH alone with 3.16-rc2, the problem can also be 
reproduced.

But I can't always reproduce it, sometimes I was able to mount subvol 
with ro,
somtimes not.

So I think the problem needs to be investigated further.

Thanks,
Qu