ctr: add ctr snapshot info <key>

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

cmd/ctr/snapshot.go

@@ -27,6 +27,7 @@ var snapshotCommand = cli.Command{
 		treeSnapshotCommand,
 		mountSnapshotCommand,
 		commitSnapshotCommand,
+		infoSnapshotCommand,
 	},
 }
 
@@ -312,6 +313,36 @@ var treeSnapshotCommand = cli.Command{
 	},
 }
 
+var infoSnapshotCommand = cli.Command{
+	Name:      "info",
+	Usage:     "get info about a snapshot",
+	ArgsUsage: "<key>",
+	Action: func(clicontext *cli.Context) error {
+		ctx, cancel := appContext(clicontext)
+		defer cancel()
+
+		if clicontext.NArg() != 1 {
+			return cli.ShowSubcommandHelp(clicontext)
+		}
+
+		key := clicontext.Args().Get(0)
+
+		snapshotter, err := getSnapshotter(clicontext)
+		if err != nil {
+			return err
+		}
+
+		info, err := snapshotter.Stat(ctx, key)
+		if err != nil {
+			return err
+		}
+
+		printAsJSON(info)
+
+		return nil
+	},
+}
+
 type snapshotTreeNode struct {
 	Name     string
 	Parent   string