rootfs: Add support for rootfs-overlay and bump to buildah v1.22.1-0.202108

Allows users to specify a readonly rootfs with :O, in exchange podman will create a writable overlay.

bump builah to v1.22.1-0.20210823173221-da2b428c56ce

[NO TESTS NEEDED]

Signed-off-by: flouthoc <flouthoc.git@gmail.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/docs/source/markdown/podman-run.1.md b/docs/source/markdown/podman-run.1.md
index 63224b49d..3a6803aaa 100644
--- a/docs/source/markdown/podman-run.1.md
+++ b/docs/source/markdown/podman-run.1.md
@@ -883,6 +883,16 @@ If specified, the first argument refers to an exploded container on the file sys
 This is useful to run a container without requiring any image management, the rootfs
 of the container is assumed to be managed externally.
 
+  `Overlay Rootfs Mounts`
+
+   The `:O` flag tells Podman to mount the directory from the rootfs path as
+storage using the `overlay file system`. The container processes
+can modify content within the mount point which is stored in the
+container storage in a separate directory. In overlay terms, the source
+directory will be the lower, and the container storage directory will be the
+upper. Modifications to the mount point are destroyed when the container
+finishes executing, similar to a tmpfs mount point being unmounted.
+
 Note: On **SELinux** systems, the rootfs needs the correct label, which is by default
 **unconfined_u:object_r:container_file_t**.
 
@@ -1791,6 +1801,12 @@ $ podman run -v /var/lib/design:/var/lib/design --group-add keep-groups ubi8
 $ podman run --name container1 --personaity=LINUX32 fedora bash
 ```
 
+### Run a container with external rootfs mounted as an overlay
+
+```
+$ podman run --name container1 --rootfs /path/to/rootfs:O bash
+```
+
 ### Rootless Containers
 
 Podman runs as a non root user on most systems. This feature requires that a new enough version of **shadow-utils**