system: add new subcommand "migrate"

it is useful to migrate existing containers to a new version of
podman.  Currently, it is needed to migrate rootless containers that
were created with podman <= 1.2 to a newer version which requires all
containers to be running in the same user namespace.

Closes: https://github.com/containers/libpod/issues/2935

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/libpod/runtime.go b/libpod/runtime.go
index 69cc10389..6d279a107 100644
--- a/libpod/runtime.go
+++ b/libpod/runtime.go
@@ -100,6 +100,8 @@ type Runtime struct {
 	// unused.
 	doRenumber bool
 
+	doMigrate bool
+
 	// valid indicates whether the runtime is ready to use.
 	// valid is set to true when a runtime is returned from GetRuntime(),
 	// and remains true until the runtime is shut down (rendering its
@@ -962,6 +964,24 @@ func makeRuntime(runtime *Runtime) (err error) {
 	// further
 	runtime.valid = true
 
+	if runtime.doMigrate {
+		if os.Geteuid() != 0 {
+			aliveLock.Unlock()
+			locked = false
+
+			became, ret, err := rootless.BecomeRootInUserNS()
+			if err != nil {
+				return err
+			}
+			if became {
+				os.Exit(ret)
+			}
+		}
+		if err := runtime.migrate(); err != nil {
+			return err
+		}
+	}
+
 	return nil
 }