linux-kernel - Re: [PATCH] ubifs: Add freeze support

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Date:   Mon, 29 May 2017 13:04:22 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Richard Weinberger <richard@....at>
Cc:     Hyunchul Lee <hyc.lee@...il.com>,
        Artem Bityutskiy <dedekind1@...il.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, kernel-team@....com,
        linux-mtd@...ts.infradead.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] ubifs: Add freeze support

On Mon, May 29, 2017 at 12:00 PM, Richard Weinberger <richard@....at> wrote:
> Amir, Hyunchul,
>
> Am 29.05.2017 um 07:40 schrieb Amir Goldstein:
>> On Mon, May 29, 2017 at 7:40 AM, Hyunchul Lee <hyc.lee@...il.com> wrote:
>>>
>>> and I missed the following case.
>>>
>>> in some embedded systems, clean-up for shutdown should be fast.
>>> during this clean-up, freeze file system to guarantee integrity.
>>> umount with MNT_DETACH is not suitable because of not killing tasks.
>
> more details please, UBIFS is designed to survive a power-cut/reboot/etc.
> at any time. How would it corrupt?
>
>> Interesting point. It seems that good old "sync; reboot" does not cut
>> it anymore.
>> Not even emergency remount read-only sysrq trigger.
>>
>> Some of you may have been following this thread on fsdevel:
>> https://www.spinics.net/lists/linux-xfs/msg06953.html
>>
>> Probably less have been following this longer thread on xfs list:
>> https://www.spinics.net/lists/linux-xfs/msg06883.html
>
> Well, UBIFS is a bit different.
> The UBIFS journal is not an add-on feature, you have to replay it in
> any case. Otherwise you're facing corrupted data.

Yes, I suppose you are right.
I guess there is no equivalent of mount -oro,{norecovery,noload} for
ubifs.

I don't know the ubifs journal implementation details.
Can ubifs_run_commit() when writers are frozen contribute to
shorter journal replay time after boot with some workloads?

Amir.