Re: [PATCH 2/2] Configure custom layers via environment variables

[Vivek Goyal <vgoyal@redhat.com>]

On Sat, Apr 18, 2020 at 12:57:27PM +0300, Amir Goldstein wrote:
> > > If I specify UNIONMOUNT_BASEDIR, then --samefs should be implied?
> > >
> >
> > This might have made sense with the meaning of UNIONMOUNT_BASEDIR
> > as it is in current posting, but with intended change, I suppose an empty
> > UNIONMOUNT_LOWERDIR could mean --samefs.
> > When both --samefs and UNIONMOUNT_LOWERDIR are specified, I'll
> > throw a warning that UNIONMOUNT_LOWERDIR is ignored.
> >
> 
> Vivek,
> 
> I updated the logic per some of your suggestions and push to:
>   https://github.com/amir73il/unionmount-testsuite/commits/overlayfs-devel
> The example of how xfstests uses it is at:
>   https://github.com/amir73il/xfstests/commits/unionmount
> 
> Since I am mostly interested in feedback on config interface, I'll just
> paste the commit message here (same text is also in README).
> 
> In short: if you set UNIONMOUNT_BASEDIR to virtiofs path and
> execute run --ov, all layers will be created under that virtiofs path.

This is nice. I tried following and it seems to work.

UNIONMOUNT_BASEDIR=/mnt/virtiofs/overlayfs-tests
UNIONMOUNT_MNTPOINT=/mnt/virtiofs/mnt

Got a question though. If somebody specifies a BASEDIR, whey not
automatically select mount point also inside that basedir. Is it because
of existing structure where basedir and mnt directory are separate and
defaults are different. Anway, I don't mind overlay mountpoint with
a separate environment variable.

> 
> Let me know if this works for you.
> Thanks,
> Amir.
> 
> commit 8c2ac6e0cd9d4b01e421375e0b9c3703e774cd9f
> Author: Amir Goldstein <amir73il@gmail.com>
> Date:   Sun Apr 12 19:22:19 2020 +0300
> 
>     Configure custom layers via environment variables
> 
>     The following environment variables are supported:
> 
>      UNIONMOUNT_BASEDIR  - parent dir of all samefs layers (default: /base)
>      UNIONMOUNT_LOWERDIR - lower layer path for non samefs (default: /lower)
>      UNIONMOUNT_MNTPOINT - mount point for executing tests (default: /mnt)
> 
>     When user provides paths for base/lower dir, they should point at
>     existing directories and their content will be deleted.
>     When the default base/lower paths are used, tmpfs instances are created.
> 
>     UNIONMOUNT_LOWERDIR is meaningless and will be ignored with --samefs.
>     Empty UNIONMOUNT_LOWERDIR with non-empty UNIONMOUNT_BASEDIR imply --samefs,

What happens if I specify both UNIONMOUNT_LOWERDIR as well as
UNIONMOUNT_BASEDIR. Does that mean only upper and work will be setup in
UNIONMOUNT_BASEDIR.

>     unless user explicitly requested non samefs setup with maxfs=<M>.

So if UNIONMOUNT_LOWERDIR is empty and I specify a UNIONMOUNT_BASEDIR and
use maxfs=<M>. All layers will still come from under UNIONMOUNT_BASEDIR,
right?

What's most intuitive to me is this.

- If user only specifies UNIONMOUNT_BASEDIR, all layers (lower, upper,
  work and even mount point) comes from that directory.

- If user specifies both UNIONMOUNT_LOWERDIR and UNIONMOUNT_BASEDIR, then
  lower layer path comes from UNIONMOUNT_LOWERDIR and rest of the layers
  come from UNIONMOUNT_BASEDIR.

- If user specifies UNIONMOUNT_MNTPOINT, it is used as overlay mount
  point. Otherwise one is selected from UNIONMOUNT_BASEDIR if user
  specified one. Otherwise "/mnt" is the default.

Thanks
Vivek

> 
>     This is going to be used for running unionmount tests from xfstests.
> 
>     Signed-off-by: Amir Goldstein <amir73il@gmail.com>
>