Re: [PATCH v3] btrfs: Introduce new mount option to disable tree log replay

["Austin S. Hemmelgarn" <ahferroin7@gmail.com>]

On 2015-12-14 12:32, David Sterba wrote:
> On Thu, Dec 10, 2015 at 10:34:06AM +0800, Qu Wenruo wrote:
>> Introduce a new mount option "nologreplay" to co-operate with "ro" mount
>> option to get real readonly mount, like "norecovery" in ext* and xfs.
>>
>> Since the new parse_options() need to check new flags at remount time,
>> so add a new parameter for parse_options().
>>
>> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
>> Reviewed-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
>> Tested-by: Austin S. Hemmelgarn <ahferroin7@gmail.com>
>
> I've read the discussions around the change and from the user's POV I'd
> suggest to add another mount option that would be just an alias for any
> mount options that would implement the 'hard-ro' semantics.
>
> Say it's called 'nowr'. Now it would imply 'nologreplay', but may cover
> more options in the future.
It should also imply noatime.  I'm not sure how BTRFS handles atime when 
mounted RO, but I know a lot of old UNIX systems updated atime even on 
filesystems mounted RO, and I know that at least at one point Linux did too.
>
>   mount -o ro,nowr /dev/sdx /mnt
>
> would work when switching kernels.

I like this idea, but I think that having a name like true-ro or hard-ro 
and making it imply ro (and noatime) would probably be better (or at 
least, simpler to use from a user perspective).