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, 14 insertions, 0 deletions

diff --git a/libpod/container_internal.go b/libpod/container_internal.go
index 7a547e565..12132cf41 100644
--- a/libpod/container_internal.go
+++ b/libpod/container_internal.go
@@ -24,6 +24,7 @@ import (
 	"github.com/containers/storage/pkg/archive"
 	"github.com/containers/storage/pkg/idtools"
 	"github.com/containers/storage/pkg/mount"
+	"github.com/coreos/go-systemd/v22/daemon"
 	securejoin "github.com/cyphar/filepath-securejoin"
 	spec "github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/opencontainers/runtime-tools/generate"
@@ -1192,6 +1193,19 @@ func (c *Container) start() error {
 
 	c.state.State = define.ContainerStateRunning
 
+	if c.config.SdNotifyMode != define.SdNotifyModeIgnore {
+		payload := fmt.Sprintf("MAINPID=%d", c.state.ConmonPID)
+		if c.config.SdNotifyMode == define.SdNotifyModeConmon {
+			payload += "\n"
+			payload += daemon.SdNotifyReady
+		}
+		if sent, err := daemon.SdNotify(false, payload); err != nil {
+			logrus.Errorf("Error notifying systemd of Conmon PID: %s", err.Error())
+		} else if sent {
+			logrus.Debugf("Notify sent successfully")
+		}
+	}
+
 	if c.config.HealthCheckConfig != nil {
 		if err := c.updateHealthStatus(define.HealthCheckStarting); err != nil {
 			logrus.Error(err)