runsc: Add the "wait" subcommand.

Users can now call "runsc wait <container id>" to wait on a particular process
inside the container. -pid can also be used to wait on a specific PID.

Manually tested the wait subcommand for a single waiter and multiple waiters
(simultaneously 2 processes waiting on the container and 2 processes waiting on
a PID within the container).

PiperOrigin-RevId: 202548978
Change-Id: Idd507c2cdea613c3a14879b51cfb0f7ea3fb3d4c

1 files changed, 23 insertions, 1 deletions

diff --git a/runsc/sandbox/sandbox.go b/runsc/sandbox/sandbox.go
index e1e7b39d1..9200fbee9 100644
--- a/runsc/sandbox/sandbox.go
+++ b/runsc/sandbox/sandbox.go
@@ -432,7 +432,29 @@ func (s *Sandbox) Wait(cid string) (syscall.WaitStatus, error) {
 	defer conn.Close()
 
 	if err := conn.Call(boot.ContainerWait, &cid, &ws); err != nil {
-		return ws, fmt.Errorf("err waiting on container %q: %v", cid, err)
+		return ws, fmt.Errorf("error waiting on container %q: %v", cid, err)
+	}
+	return ws, nil
+}
+
+// WaitPID waits for process 'pid' in the container's sandbox and returns its
+// WaitStatus.
+func (s *Sandbox) WaitPID(pid int32, cid string) (syscall.WaitStatus, error) {
+	log.Debugf("Waiting for PID %d in sandbox %q", pid, s.ID)
+	var ws syscall.WaitStatus
+	conn, err := s.connect()
+	if err != nil {
+		return ws, err
+	}
+	defer conn.Close()
+
+	args := &boot.WaitPIDArgs{
+		PID: pid,
+		CID: cid,
+	}
+
+	if err := conn.Call(boot.ContainerWaitPID, args, &ws); err != nil {
+		return ws, fmt.Errorf("error waiting on PID %d in sandbox %q: %v", pid, s.ID, err)
 	}
 
 	if s.IsRootContainer(cid) {