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

[Amir Goldstein <amir73il@gmail.com>]

On Mon, Apr 20, 2020 at 10:15 PM Vivek Goyal <vgoyal@redhat.com> wrote:
>
> 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.
>

No reason. I think it's a good idea. I'll do it.

> >
> > 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.
>

Yes, work and upper and with --ov=N also middle layers.

> >     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?

Yes, but note that while the *path* of all layers is under UNIONMOUNT_BASEDIR,
namely $UNIONMOUNT_BASEDIR/$N/{u,w}, some layers will use the basedir fs,
while others will have a tmpfs instance mounted at $UNIONMOUNT_BASEDIR/$N/.
M from maxfs=<M> determines the number of middle layers using tmpfs instances.

Now that I think about it, this setup should use $UNIONMOUNT_BASEDIR/lower
as lowerdir path and it uses /lower.
I'll need to fix that.

>
> 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.

OK.

>
> - 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.

DONE.

>
> - 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.
>

OK.

Thanks for valuable feedback,
Amir.