Re: [PATCH RESEND] ubifs: Introduce a mount option of force_atime.

[Dongsheng Yang <yangds.fnst@cn.fujitsu.com>]

On 06/10/2015 06:25 PM, Artem Bityutskiy wrote:
> On Wed, 2015-06-10 at 18:10 +0800, Dongsheng Yang wrote:
>> On 06/10/2015 05:21 PM, Artem Bityutskiy wrote:
>>> On Wed, 2015-06-10 at 11:16 +0800, Dongsheng Yang wrote:
>>>> Therefore, I introduced a new option named as force_atime in ubifs.
>>>> That's a ubifs-dependent opiton and it works as a main switch, in
>>>> a higher level compared with atime and noatime. If force_atime, we
>>>> support the atime-related flags. Otherwise, we don't care about all of
>>>> them in flags and don't support atime anyway.
>>>
>>> How bad is it to just default to relatime like other file-systems do,
>>> comparing to what we have now?
>>
>> Ha, yes, that's a problem. I read it from wiki that the author think
>> it's bad for ubifs. But I did not do a measure about it.
>
> Since I am one of the authors, I think we were mostly looking at the
> full atime support, and did not really look at relatime.
>
>> In theory, yes, lots of writing would damage the flash. So I think
>> just make it optional to user is a flexible way to do it. Even we
>> want to make the default to relatime, I think it's better to keep
>> the compatibility for a period and provide a force_atime to user.
>>
>> When lots of users said "okey, we are mostly choosing force_atime in our
>> use cases.". I believe that's a safe way to make ubifs supporting
>> atime by default.
>
> Let me make a step back. So what I hear is that the problem is that you
> cannot find the original mount options. For example, when you see the
> MNT_RELATIME flag, you do not know whether it was specified by the user
> or it was VFS adding this flag. Is this correct?
>
> If it is correct, then I think we need to look at a VFS-level solution.
> If the above is the only problem, then I'd say that introducing a custom
> "force_atime" is a work-around for VFS limitations.

That's correct. Yes, I really want to solve it in vfs at first. But
later, just submited this patch as a Problem-solved for us. Because I
thought the force_atime would disappear when we decide to support
atime by default in future.

Besides a change in VFS would cause more discussion, after a trade-off,
I submitted this patch for ubifs. :)

But yes, there is really, at leat, a TODO entry for VFS in this
scenario I think. If you think we need to do it rather than a
work-around as what this patch did. I will think a better way
in VFS for that. :)

Thanx
Yang
>
> Artem.
>
> .
>