Re: [PATCH] overlay: Implement volatile-specific fsync error behaviour

[Amir Goldstein <amir73il@gmail.com>]

> I asked this question in last email as well. errseq_sample() will return
> 0 if current error has not been seen yet. That means next time a sync
> call comes for volatile mount, it will return an error. But that's
> not what we want. When we mounted a volatile overlay, if there is an
> existing error (seen/unseen), we don't care. We only care if there
> is a new error after the volatile mount, right?
>
> I guess we will need another helper similar to errseq_smaple() which
> just returns existing value of errseq. And then we will have to
> do something about errseq_check() to not return an error if "since"
> and "eseq" differ only by "seen" bit.
>
> Otherwise in current form, volatile mount will always return error
> if upperdir has error and it has not been seen by anybody.
>
> How did you finally end up testing the error case. Want to simualate
> error aritificially and test it.
>

Good spotting!

Besides the specialized test for sync error,
I wonder if anybody ever tested "volatile" setup with xfstests or unionmount?

In xfsftest can set envvar OVERLAY_MOUNT_OPTIONS="-o volatile"

In unionmount I have a branch [1] with support for envvar
UNIONMOUNT_MNTOPTIONS.

I did not merge this change to master because nobody (but me) tested
it, so that would be a good opportunity (hint hint)

Thanks,
Amir.

[1] https://github.com/amir73il/unionmount-testsuite/commits/envvars