Re: [PATCH v2] ovl: return error on mount if metacopy cannot be enabled

[Vivek Goyal <vgoyal@redhat.com>]

On Wed, Oct 31, 2018 at 06:04:36PM +0200, Amir Goldstein wrote:
> > Ok. So basically strict and metacopy has no connection but we want to
> > take this opportunity to enable more sane overlayfs behavior by default
> > without breaking backward compatibility.
> >
> > And if a corner case user does not like implicit strict=on, they can
> > specifically do "metacopy=on,strict=off".
> >
> 
> Yes, but keep in mind that strict=off will NOT be applied to stable
> v4.19.y *unless* a real user really reports a bug, a-priori, we assume
> that implicit metacopy=on => redirect_dir=on,strict=on is sufficient
> to solve the bug, so it is sufficient for stable.

Did not understand this. So strict=on will be in stable or not? I mean,
all the behavior strict=on enforces will be in 4.19 or not.

If it is not, then it will become backward compatibility issue by the
time 4.20 releases.

If strict=on is not part of 4.19 stable, then you can't switch it
on in 4.20.

What am I missing.

> 
> > I am fine with this. Thanks.
> >
> > So every new mount option now will enable strict=on implicitly?
> >
> 
> Correct. For example:
> 
> 
> @@ -109,6 +109,7 @@ config OVERLAY_FS_METACOPY
>         bool "Overlayfs: turn on metadata only copy up feature by default"
>         depends on OVERLAY_FS
>         select OVERLAY_FS_REDIRECT_DIR
> +       select OVERLAY_FS_STRICT
>         help
>           If this config option is enabled then overlay filesystems will
>           copy up only metadata where appropriate and data copy up will
> 
> ...
> 
> @@ -560,6 +599,10 @@ static int ovl_parse_opt(char *opt, struct
> ovl_config *config)
>                 }
>         }
> 
> +       /* We must honor user explicit request to enable metacopy */
> +       if (config->metacopy && !ovl_metacopy_def)
> +               config->strict = true;
> +

So if a user loads module with metacopy=on and also specifies metacopy=on
mount option, then strict will not be enforced?

Thanks
Vivek