stats: list all running containers unless specified otherwise

Unless specified otherwise by --all, --latest or via arguments, list all
running containers.  This matches the behaviour of Docker and is also
illustrated in the man pages where containers and options are marked to
be optional.

Fixes: containers#4274
Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

cmd/podman/stats.go

@@ -44,9 +44,6 @@ var (
 			statsCommand.Remote = remoteclient
 			return statsCmd(&statsCommand)
 		},
-		Args: func(cmd *cobra.Command, args []string) error {
-			return checkAllAndLatest(cmd, args, false)
-		},
 		Example: `podman stats --all --no-stream
   podman stats ctrID
   podman stats --no-stream --format "table {{.ID}} {{.Name}} {{.MemUsage}}" ctrID`,
@@ -92,8 +89,6 @@ func statsCmd(c *cliconfig.StatsValues) error {
 
 	if ctr > 1 {
 		return errors.Errorf("--all, --latest and containers cannot be used together")
-	} else if ctr == 0 {
-		return errors.Errorf("you must specify --all, --latest, or at least one container")
 	}
 
 	runtime, err := libpodruntime.GetRuntime(getContext(), &c.PodmanCommand)

test/e2e/stats_test.go

@@ -11,6 +11,8 @@ import (
 	. "github.com/onsi/gomega"
 )
 
+// TODO: we need to check the output. Currently, we only check the exit codes
+// which is not enough.
 var _ = Describe("Podman stats", func() {
 	var (
 		tempdir    string
@@ -61,6 +63,15 @@ var _ = Describe("Podman stats", func() {
 		Expect(session.ExitCode()).To(Equal(0))
 	})
 
+	It("podman stats on all running containers", func() {
+		session := podmanTest.RunTopContainer("")
+		session.WaitWithDefaultTimeout()
+		Expect(session.ExitCode()).To(Equal(0))
+		session = podmanTest.Podman([]string{"stats", "--no-stream"})
+		session.WaitWithDefaultTimeout()
+		Expect(session.ExitCode()).To(Equal(0))
+	})
+
 	It("podman stats only output cids", func() {
 		session := podmanTest.RunTopContainer("")
 		session.WaitWithDefaultTimeout()