buildkit: add from= field to bind and cache mounts so images can be used as source

[flouthoc]

Following commit adds buildkit like support for from field to --mount=type=bind
and --mount=type=cache so images and stage can be used as mount source.

Usage looks like

RUN --mount=type=bind,source=.,from=<your-image>,target=/path ls /path

and

RUN --mount=type=cache,from=<your-image>,target=/path ls /path

Closes: #3501

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[flouthoc]

@nalind @TomSweeneyRedHat Made requested corrections. Could you please take a look again.

[TomSweeneyRedHat]

LGTM
@nalind does it LGTY?

[nalind]

The tests need to also exercise source values other than ".", including paths that start with "/", "./", and other values (all of which they need to verify are interpreted as being relative to root of the image or stage specified for the "from"). They also need to check that from values that reference other stages in multi-stage builds work as expected. These options should also be tested with buildah run, where "from" should probably be able to point to other containers, to line up with how the --from flag is treated for buildah copy.

[flouthoc]

@nalind Thanks i'll get these tests in.

[flouthoc]

The tests need to also exercise source values other than ".", including paths that start with "/", "./", and other values (all of which they need to verify are interpreted as being relative to root of the image or stage specified for the "from"). They also need to check that from values that reference other stages in multi-stage builds work as expected. These options should also be tested with buildah run, where "from" should probably be able to point to other containers, to line up with how the --from flag is treated for buildah copy.

@nalind Added requested tests.

I would also request you to take a look at commit 3941014 which makes sure we use common selinux label across all containers/builders spawned under a common Executor session. Its needed to mount different stages.

[nalind]

I'm not entirely sure we've got the behavior right for writable bind mounts, otherwise LGTM.

[flouthoc]

I'm not entirely sure we've got the behavior right for writable bind mounts, otherwise LGTM.

Me and @nalind discussed this, so our design has some limitation on rw on bind mounts for images. Future solution could be something on the lines of overlay on top of build context but that will be new feature and on a different PR. @nalind Please correct me if i got this right or not.

@containers/build-maintainers @rhatdan @TomSweeneyRedHat PTAL

[rhatdan]

Is there no way to consolidate this code together, this is the third time you have code to walk the arg list?

[flouthoc]

@rhatdan I agree we can reduce redundancy. Some of the options are not supported in other mounts so switch case is slightly different for each one.

However parsing is legacy code this is just a move around. So to prevent huge diff would it work if i do that in a follow up
PR where I will also fix selinux issue.

[rhatdan]

@flouthoc needs rebase.

[flouthoc]

I'm not entirely sure we've got the behavior right for writable bind mounts, otherwise LGTM.

@nalind This is implemented in latest commit also added a test to verify this.

buildah/tests/bud.bats

Line 3743 in fb163aa

@test "bud-with-writeable-mount-bind-from-like-buildkit" {

[rhatdan]

Sadly @flouthoc needs a rebase.

[rhatdan]

/lgtm