slirp: Avoid zombie processes after fork_exec

Slirp uses fork_exec for spawning service processes, and QEMU uses this
for running smbd. As SIGCHLD is not handled, these processes become
zombies on termination. Fix this by installing a proper signal handler,
but also make sure we disable the signal while waiting on forked network
setup/shutdown scripts.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Mark McLoughlin <markmc@redhat.com>

1 files changed, 11 insertions, 2 deletions

diff --git a/vl.c b/vl.c
index fcf853222..a5f966d4c 100644
--- a/vl.c
+++ b/vl.c
@@ -4783,7 +4783,12 @@ static void termsig_handler(int signal)
     qemu_system_shutdown_request();
 }
 
-static void termsig_setup(void)
+static void sigchld_handler(int signal)
+{
+    waitpid(-1, NULL, WNOHANG);
+}
+
+static void sighandler_setup(void)
 {
     struct sigaction act;
 
@@ -4792,6 +4797,10 @@ static void termsig_setup(void)
     sigaction(SIGINT,  &act, NULL);
     sigaction(SIGHUP,  &act, NULL);
     sigaction(SIGTERM, &act, NULL);
+
+    act.sa_handler = sigchld_handler;
+    act.sa_flags = SA_NOCLDSTOP;
+    sigaction(SIGCHLD, &act, NULL);
 }
 
 #endif
@@ -5918,7 +5927,7 @@ int main(int argc, char **argv, char **envp)
 
 #ifndef _WIN32
     /* must be after terminal init, SDL library changes signal handlers */
-    termsig_setup();
+    sighandler_setup();
 #endif
 
     /* Maintain compatibility with multiple stdio monitors */