Re: [PATCH 0/2] overlayfs: C/R enhancements

[Amir Goldstein]

On Thu, Jun 4, 2020 at 7:13 PM Alexander Mikhalitsyn
<alexander.mikhalitsyn@xxxxxxxxxxxxx> wrote:
>
> This patchset aimed to make C/R of overlayfs mounts with CRIU possible.
> We introduce two new overlayfs module options -- dyn_path_opts and
> mnt_id_path_opts. If enabled this options allows to see real *full* paths
> in lowerdir, workdir, upperdir options, and also mnt_ids for corresponding
> paths.
>
> This changes should not break anything because for showing mnt_ids we simply
> introduce new show-time mount options. And for paths we simply *always*
> provide *full paths* instead of relative path on mountinfo.
>
> BEFORE
>
> overlay on /var/lib/docker/overlay2/XYZ/merged type overlay (rw,relatime,
> lowerdir=/var/lib/docker/overlay2/XYZ-init/diff:/var/lib/docker/overlay2/
> ABC/diff,upperdir=/var/lib/docker/overlay2/XYZ/diff,workdir=/var/lib/docker
> /overlay2/XYZ/work)
> none on /sys type sysfs (rw,relatime)
>
> AFTER
>
> overlay on /var/lib/docker/overlay2/XYZ/merged type overlay (rw,relatime,
> lowerdir=/var/lib/docker/overlay2/XYZ-init/diff:/var/lib/docker/overlay2/
> ABC/diff,upperdir=/var/lib/docker/overlay2/XYZ/diff,workdir=/var/lib/docker
> /overlay2/XYZ/work,lowerdir_mnt_id=175:175,upperdir_mnt_id=175)
> none on /sys type sysfs (rw,relatime)
>

But overlayfs won't accept these "output only" options as input args,
which is a problem.

Wouldn't it be better for C/R to implement mount options
that overlayfs can parse and pass it mntid and fhandle instead
of paths?
I believe C/R is using a similar method to export inotify/fanotify
marks.

FWIW overlayfs already has utilities that encode filehandle to
text and back, see  ovl_get_index_name().

Thanks,
Amir.