bhyve: monitor: detect monitor exit

Currently, sending SIGTERM to the bhyve process triggers ACPI poweroff
for a VM. However, when running bhyve in monitor mode (-M), there are
two processes: the monitor process and the actual VM process. Sending
SIGTERM to the VM process works as before -- it powers off the VM.
But sending SIGTERM to the monitor process just kills the monitor
process, leaving the stale VM process running.

Fix that by creating a pipe between these two processes. The child
process uses the pipe to detect when the monitor goes away, and exits
automatically.

MFC after:		2 weeks
Reviewed by:		markj
Sponsored by:		The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D58788

1 files changed, 37 insertions, 4 deletions

diff --git a/usr.sbin/bhyve/bhyverun.c b/usr.sbin/bhyve/bhyverun.c
index c089d1fbc8fa..339cf5071906 100644
--- a/usr.sbin/bhyve/bhyverun.c
+++ b/usr.sbin/bhyve/bhyverun.c
@@ -54,9 +54,7 @@
 #include <string.h>
 #include <err.h>
 #include <errno.h>
-#ifdef BHYVE_SNAPSHOT
 #include <fcntl.h>
-#endif
 #include <libgen.h>
 #include <libutil.h>
 #include <unistd.h>
@@ -127,6 +125,29 @@ static struct vcpu_info {
 
 static cpuset_t **vcpumap;
 
+static void
+monitor_pipe_handler(int fd __unused, enum ev_type type __unused,
+    void *param __unused)
+{
+
+	exit(BHYVE_EXIT_ERROR);
+}
+
+static void
+monitor_pipe_init(int fd)
+{
+#ifndef WITHOUT_CAPSICUM
+	cap_rights_t rights;
+
+	cap_rights_init(&rights, CAP_EVENT);
+	if (caph_rights_limit(fd, &rights) == -1)
+		err(BHYVE_EXIT_ERROR, "Unable to apply rights to monitor pipe");
+#endif
+
+	if (mevent_add(fd, EVF_READ, monitor_pipe_handler, NULL) == NULL)
+		errx(BHYVE_EXIT_ERROR, "Unable to register parent exit event");
+}
+
 /*
  * XXX This parser is known to have the following issues:
  * 1.  It accepts null key=value tokens ",," as setting "cpus" to an
@@ -922,17 +943,29 @@ main(int argc, char *argv[])
 	init_bootrom(ctx);
 
 	if (get_config_bool_default("monitor", false)) {
+		int monitor_pipe[2];
+		pid_t child;
+
 		while (1) {
-			pid_t child = fork();
+			if (pipe2(monitor_pipe, O_CLOEXEC) == -1)
+				err(BHYVE_EXIT_ERROR, "pipe2");
+
+			child = fork();
 			if (child == -1) {
 				EPRINTLN("Monitor mode fork failed: %s",
 				    strerror(errno));
 				exit(BHYVE_EXIT_ERROR);
 			}
-			if (child == 0)
+			if (child == 0) {
+				close(monitor_pipe[1]);
+				monitor_pipe_init(monitor_pipe[0]);
 				break;
+			}
+
+			close(monitor_pipe[0]);
 			while ((error = waitpid(child, &status, 0)) == -1 && errno == EINTR)
 			    ;
+			close(monitor_pipe[1]);
 			if (error == -1) {
 				EPRINTLN("Monitor mode wait failed: %s",
 				    strerror(errno));