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>

3 files changed, 84 insertions, 0 deletions

diff --git a/libpod/options.go b/libpod/options.go
index 8038f1935..949894dcb 100644
--- a/libpod/options.go
+++ b/libpod/options.go
@@ -436,6 +436,22 @@ func WithRenumber() RuntimeOption {
 	}
 }
 
+// WithMigrate instructs libpod to perform a lock migrateing while
+// initializing. This will handle migrations from early versions of libpod with
+// file locks to newer versions with SHM locking, as well as changes in the
+// number of configured locks.
+func WithMigrate() RuntimeOption {
+	return func(rt *Runtime) error {
+		if rt.valid {
+			return ErrRuntimeFinalized
+		}
+
+		rt.doMigrate = true
+
+		return nil
+	}
+}
+
 // Container Creation Options
 
 // WithShmDir sets the directory that should be mounted on /dev/shm.
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
 }
 
diff --git a/libpod/runtime_migrate.go b/libpod/runtime_migrate.go
new file mode 100644
index 000000000..7d7fa108d
--- /dev/null
+++ b/libpod/runtime_migrate.go
@@ -0,0 +1,48 @@
+package libpod
+
+import (
+	"context"
+	"path/filepath"
+
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+)
+
+func (r *Runtime) migrate() error {
+	runningContainers, err := r.GetRunningContainers()
+	if err != nil {
+		return err
+	}
+
+	allCtrs, err := r.state.AllContainers()
+	if err != nil {
+		return err
+	}
+
+	logrus.Infof("stopping all containers")
+	for _, ctr := range runningContainers {
+		logrus.Infof("stopping %s", ctr.ID())
+		if err := ctr.Stop(); err != nil {
+			return errors.Wrapf(err, "cannot stop container %s", ctr.ID())
+		}
+	}
+
+	for _, ctr := range allCtrs {
+		oldLocation := filepath.Join(ctr.state.RunDir, "conmon.pid")
+		if ctr.config.ConmonPidFile == oldLocation {
+			logrus.Infof("changing conmon PID file for %s", ctr.ID())
+			ctr.config.ConmonPidFile = filepath.Join(ctr.config.StaticDir, "conmon.pid")
+			if err := r.state.RewriteContainerConfig(ctr, ctr.config); err != nil {
+				return errors.Wrapf(err, "error rewriting config for container %s", ctr.ID())
+			}
+		}
+	}
+
+	for _, ctr := range runningContainers {
+		if err := ctr.Start(context.Background(), true); err != nil {
+			logrus.Errorf("error restarting container %s", ctr.ID())
+		}
+	}
+
+	return nil
+}