cmd/run: Optimize 'enter' and 'run' for already running containers

Currently, the 'enter' and 'run' commands always invoke 'podman start'
even if the Toolbx container's entry point is already running.  There's
no need for that.  The commands already invoke 'podman inspect' to find
out if the org.freedesktop.Flatpak.SessionHelper D-Bus service needs to
be started.  Thus, they already have what is needed to find out if the
container is stopped and 'podman start' is necessary before it can be
used with 'podman exec', or if it's already running.

The unconditional 'podman start' invocation was followed by a second
'podman inspect' invocation to find out if the 'podman start' managed to
start the container's entry point.  There's no need for this second
'podman inspect' either, just like the 'podman start', when it's already
known from the first 'podman inspect' that the container is running.

The extra 'podman start' and 'podman inspect' invocations are
sufficiently expensive to add a noticeable overhead to the 'enter' and
'run' commands.  It's common to use a container that's already running,
just like having multiple terminals with the same working directory, and
terminal emulation applications like Ptyxis try to make it easier [1].
Therefore, it's worth optimizing this code path.

[1] https://gitlab.gnome.org/chergert/ptyxis
    https://flathub.org/apps/app.devsuite.Ptyxis

#1070

src/cmd/run.go

@@ -237,20 +237,16 @@ func runCommand(container string,
 		}
 	}
 
-	if err := callFlatpakSessionHelper(container); err != nil {
-		return err
-	}
-
-	logrus.Debugf("Starting container %s", container)
-	if err := startContainer(container); err != nil {
-		return err
-	}
-
-	entryPoint, entryPointPID, err := getEntryPointAndPID(container)
+	logrus.Debugf("Inspecting container %s", container)
+	containerObj, err := podman.InspectContainer(container)
 	if err != nil {
-		return err
+		return fmt.Errorf("failed to inspect container %s", container)
 	}
 
+	entryPoint := containerObj.EntryPoint()
+	entryPointPID := containerObj.EntryPointPID()
+	logrus.Debugf("Entry point of container %s is %s (PID=%d)", container, entryPoint, entryPointPID)
+
 	if entryPoint != "toolbox" {
 		var builder strings.Builder
 		fmt.Fprintf(&builder, "container %s is too old and no longer supported \n", container)
@@ -260,11 +256,31 @@ func runCommand(container string,
 		return errors.New(errMsg)
 	}
 
-	if entryPointPID <= 0 {
-		return fmt.Errorf("invalid entry point PID of container %s", container)
+	if err := callFlatpakSessionHelper(containerObj); err != nil {
+		return err
 	}
 
-	logrus.Debugf("Waiting for container %s to finish initializing", container)
+	if entryPointPID <= 0 {
+		logrus.Debugf("Starting container %s", container)
+		if err := startContainer(container); err != nil {
+			return err
+		}
+
+		logrus.Debugf("Inspecting container %s", container)
+		containerObj, err := podman.InspectContainer(container)
+		if err != nil {
+			return fmt.Errorf("failed to inspect container %s", container)
+		}
+
+		entryPointPID = containerObj.EntryPointPID()
+		logrus.Debugf("Entry point of container %s is %s (PID=%d)", container, entryPoint, entryPointPID)
+
+		if entryPointPID <= 0 {
+			return fmt.Errorf("invalid entry point PID of container %s", container)
+		}
+
+		logrus.Debugf("Waiting for container %s to finish initializing", container)
+	}
 
 	toolboxRuntimeDirectory, err := utils.GetRuntimeDirectory(currentUser)
 	if err != nil {
@@ -430,17 +446,13 @@ func runHelp(cmd *cobra.Command, args []string) {
 	}
 }
 
-func callFlatpakSessionHelper(container string) error {
-	logrus.Debugf("Inspecting mounts of container %s", container)
-
-	containerObj, err := podman.InspectContainer(container)
-	if err != nil {
-		return fmt.Errorf("failed to inspect entry point of container %s", container)
-	}
+func callFlatpakSessionHelper(container podman.Container) error {
+	name := container.Name()
+	logrus.Debugf("Inspecting mounts of container %s", name)
 
 	var needsFlatpakSessionHelper bool
 
-	mounts := containerObj.Mounts()
+	mounts := container.Mounts()
 	for _, mount := range mounts {
 		if mount == "/run/host/monitor" {
 			logrus.Debug("Requires org.freedesktop.Flatpak.SessionHelper")
@@ -522,22 +534,6 @@ func constructExecArgs(container, preserveFDs string,
 	return execArgs
 }
 
-func getEntryPointAndPID(container string) (string, int, error) {
-	logrus.Debugf("Inspecting entry point of container %s", container)
-
-	containerObj, err := podman.InspectContainer(container)
-	if err != nil {
-		return "", 0, fmt.Errorf("failed to inspect entry point of container %s", container)
-	}
-
-	entryPoint := containerObj.EntryPoint()
-	entryPointPID := containerObj.EntryPointPID()
-
-	logrus.Debugf("Entry point of container %s is %s (PID=%d)", container, entryPoint, entryPointPID)
-
-	return entryPoint, entryPointPID, nil
-}
-
 func isCommandPresent(container, command string) (bool, error) {
 	logrus.Debugf("Looking up command %s in container %s", command, container)