Implement --sdnotify cmdline option to control sd-notify behavior

--sdnotify container|conmon|ignore
With "conmon", we send the MAINPID, and clear the NOTIFY_SOCKET so the OCI
runtime doesn't pass it into the container. We also advertise "ready" when the
OCI runtime finishes to advertise the service as ready.

With "container", we send the MAINPID, and leave the NOTIFY_SOCKET so the OCI
runtime passes it into the container for initialization, and let the container advertise further metadata.
This is the default, which is closest to the behavior podman has done in the past.

The "ignore" option removes NOTIFY_SOCKET from the environment, so neither podman nor
any child processes will talk to systemd.

This removes the need for hardcoded CID and PID files in the command line, and
the PIDFile directive, as the pid is advertised directly through sd-notify.

Signed-off-by: Joseph Gooch <mrwizard@dok.org>

1 files changed, 24 insertions, 6 deletions

diff --git a/libpod/oci_conmon_linux.go b/libpod/oci_conmon_linux.go
index 98e436e78..534622382 100644
--- a/libpod/oci_conmon_linux.go
+++ b/libpod/oci_conmon_linux.go
@@ -30,6 +30,7 @@ import (
 	"github.com/containers/libpod/v2/utils"
 	pmount "github.com/containers/storage/pkg/mount"
 	"github.com/coreos/go-systemd/v22/activation"
+	"github.com/coreos/go-systemd/v22/daemon"
 	spec "github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/opencontainers/selinux/go-selinux"
 	"github.com/opencontainers/selinux/go-selinux/label"
@@ -365,8 +366,10 @@ func (r *ConmonOCIRuntime) StartContainer(ctr *Container) error {
 		return err
 	}
 	env := []string{fmt.Sprintf("XDG_RUNTIME_DIR=%s", runtimeDir)}
-	if notify, ok := os.LookupEnv("NOTIFY_SOCKET"); ok {
-		env = append(env, fmt.Sprintf("NOTIFY_SOCKET=%s", notify))
+	if ctr.config.SdNotifyMode == define.SdNotifyModeContainer {
+		if notify, ok := os.LookupEnv("NOTIFY_SOCKET"); ok {
+			env = append(env, fmt.Sprintf("NOTIFY_SOCKET=%s", notify))
+		}
 	}
 	if path, ok := os.LookupEnv("PATH"); ok {
 		env = append(env, fmt.Sprintf("PATH=%s", path))
@@ -887,6 +890,12 @@ func (r *ConmonOCIRuntime) createOCIContainer(ctr *Container, restoreOptions *Co
 		}
 	}
 
+	if ctr.config.SdNotifyMode == define.SdNotifyModeIgnore {
+		if err := os.Unsetenv("NOTIFY_SOCKET"); err != nil {
+			logrus.Warnf("Error unsetting NOTIFY_SOCKET %s", err.Error())
+		}
+	}
+
 	args := r.sharedConmonArgs(ctr, ctr.ID(), ctr.bundlePath(), filepath.Join(ctr.state.RunDir, "pidfile"), ctr.LogPath(), r.exitsDir, ociLog, ctr.LogDriver(), logTag)
 
 	if ctr.config.Spec.Process.Terminal {
@@ -940,7 +949,7 @@ func (r *ConmonOCIRuntime) createOCIContainer(ctr *Container, restoreOptions *Co
 	}
 
 	// 0, 1 and 2 are stdin, stdout and stderr
-	conmonEnv, envFiles, err := r.configureConmonEnv(runtimeDir)
+	conmonEnv, envFiles, err := r.configureConmonEnv(ctr, runtimeDir)
 	if err != nil {
 		return err
 	}
@@ -1034,6 +1043,13 @@ func (r *ConmonOCIRuntime) createOCIContainer(ctr *Container, restoreOptions *Co
 		// conmon not having a pid file is a valid state, so don't set it if we don't have it
 		logrus.Infof("Got Conmon PID as %d", conmonPID)
 		ctr.state.ConmonPID = conmonPID
+		if ctr.config.SdNotifyMode != define.SdNotifyModeIgnore {
+			if sent, err := daemon.SdNotify(false, fmt.Sprintf("MAINPID=%d", conmonPID)); err != nil {
+				logrus.Errorf("Error notifying systemd of Conmon PID: %s", err.Error())
+			} else if sent {
+				logrus.Debugf("Notify MAINPID sent successfully")
+			}
+		}
 	}
 
 	if ctr.config.PreserveFDs > 0 {
@@ -1137,7 +1153,7 @@ func prepareProcessExec(c *Container, cmd, env []string, tty bool, cwd, user, se
 
 // configureConmonEnv gets the environment values to add to conmon's exec struct
 // TODO this may want to be less hardcoded/more configurable in the future
-func (r *ConmonOCIRuntime) configureConmonEnv(runtimeDir string) ([]string, []*os.File, error) {
+func (r *ConmonOCIRuntime) configureConmonEnv(ctr *Container, runtimeDir string) ([]string, []*os.File, error) {
 	env := make([]string, 0, 6)
 	env = append(env, fmt.Sprintf("XDG_RUNTIME_DIR=%s", runtimeDir))
 	env = append(env, fmt.Sprintf("_CONTAINERS_USERNS_CONFIGURED=%s", os.Getenv("_CONTAINERS_USERNS_CONFIGURED")))
@@ -1149,8 +1165,10 @@ func (r *ConmonOCIRuntime) configureConmonEnv(runtimeDir string) ([]string, []*o
 	env = append(env, fmt.Sprintf("HOME=%s", home))
 
 	extraFiles := make([]*os.File, 0)
-	if notify, ok := os.LookupEnv("NOTIFY_SOCKET"); ok {
-		env = append(env, fmt.Sprintf("NOTIFY_SOCKET=%s", notify))
+	if ctr.config.SdNotifyMode == define.SdNotifyModeContainer {
+		if notify, ok := os.LookupEnv("NOTIFY_SOCKET"); ok {
+			env = append(env, fmt.Sprintf("NOTIFY_SOCKET=%s", notify))
+		}
 	}
 	if !r.sdNotify {
 		if listenfds, ok := os.LookupEnv("LISTEN_FDS"); ok {