Add support for 'image' volume driver

We added the concept of image volumes in 2.2.0, to support
inspecting an image from within a container. However, this is a
strictly read-only mount, with no modification allowed.

By contrast, the new `image` volume driver creates a c/storage
container as its underlying storage, so we have a read/write
layer. This, in and of itself, is not especially interesting, but
what it will enable in the future is. If we add a new command to
allow these image volumes to be committed, we can now distribute
volumes - and changes to them - via a standard OCI image registry
(which is rather new and quite exciting).

Future work in this area:
- Add support for `podman volume push` (commit volume changes and
  push resulting image to OCI registry).
- Add support for `podman volume pull` (currently, we require
  that the image a volume is created from be already pulled; it
  would be simpler if we had a dedicated command that did the
  pull and made a volume from it)
- Add support for scratch images (make an empty image on demand
  to use as the base of the volume)
- Add UOR support to `podman volume push` and
  `podman volume pull` to enable both with non-image volume
  drivers

Signed-off-by: Matthew Heon <matthew.heon@pm.me>

1 files changed, 3 insertions, 0 deletions

diff --git a/libpod/runtime.go b/libpod/runtime.go
index 83c9f53e2..f250d759c 100644
--- a/libpod/runtime.go
+++ b/libpod/runtime.go
@@ -1091,6 +1091,9 @@ func (r *Runtime) getVolumePlugin(volConfig *VolumeConfig) (*plugin.VolumePlugin
 
 	pluginPath, ok := r.config.Engine.VolumePlugins[name]
 	if !ok {
+		if name == define.VolumeDriverImage {
+			return nil, nil
+		}
 		return nil, fmt.Errorf("no volume plugin with name %s available: %w", name, define.ErrMissingPlugin)
 	}