Re: [PATCH v6 03/15] ovl: Provide a mount option metacopy=on/off for metadata copyup

[Amir Goldstein <amir73il@gmail.com>]

On Fri, Nov 10, 2017 at 9:07 AM, Amir Goldstein <amir73il@gmail.com> wrote:
> On Thu, Nov 9, 2017 at 10:50 PM, Vivek Goyal <vgoyal@redhat.com> wrote:
>> By default metadata only copy up is disabled. Provide a mount option so
>> that users can choose one way or other.
>>
>> Also provide a kernel config and module option to enable/disable
>> metacopy feature.
>>
>> Like index feature, we verify on mount that upper root is not being
>> reused with a different lower root. This hopes to get the configuration
>> right and detect the copied layers use case. But this does only so
>> much as we don't verify all the lowers. So it is possible that a lower is
>> missing and later data copy up fails.
>>
>> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
>
> Fine, as long as Miklos agrees not to enforce exclusive dir lock,
> it's fine by me.
>
> Please take a look at my ovl-features patches and say what you think.
> It is time we started to enforce some order with all the inter-dependencies
> between features.
> With my proposal, it will make mounting an overlay with metacopy object
> on older kernel slightly harder (but not impossible), so it can help admins
> from tripping over themselves.
>
> Reviewed-by: Amir Goldstein <amir73il@gmail.com>
>

On second though, hold that Reviewed-by, there is one more thing
that this patch should check, see path:
"ovl: disable redirect_dir and index when no xattr support"
from my verify_dir patches:
https://github.com/amir73il/linux/commits/ovl-verify-dir

You may cherry-pick it at beginning of your series and then this
patch should also disable metacopy on mount with noxattr with a warning to user,
instead of silently not doing the metacopies, but claiming in mount options that
metacopy is on.

Thanks,
Amir.