lib: daemonize more intelligently

Block the parent process until the child has reached the main loop, e.g.
full service is available.

This means it's no longer neccessary to add a "safety sleep" for daemon
cross-dependencies, when using the -d startup option.  This doesn't help
if -d isn't used.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>

diff --git a/lib/libfrr.c b/lib/libfrr.c
index 022296b3fbc886ba38f702ff2c06e4ee07b72adc..73580b8a086427d406087eca916e31d5d74e90b3 100644 (file)
--- a/lib/libfrr.c
+++ b/lib/libfrr.c
@@ -20,6 +20,9 @@
 
 #include <zebra.h>
 
+#include <sys/types.h>
+#include <sys/wait.h>
+
 #include "libfrr.h"
 #include "getopt.h"
 #include "vty.h"
@@ -29,6 +32,7 @@
 #include "zclient.h"
 #include "log_int.h"
 #include "module.h"
+#include "network.h"
 
 DEFINE_HOOK(frr_late_init, (struct thread_master * tm), (tm))
 
@@ -367,6 +371,77 @@ struct thread_master *frr_init(void)
        return master;
 }
 
+static void frr_daemon_wait(int fd)
+{
+       struct pollfd pfd[1];
+       int ret;
+       pid_t exitpid;
+       int exitstat;
+
+       do {
+               pfd[0].fd = fd;
+               pfd[0].events = POLLIN;
+
+               ret = poll(pfd, 1, -1);
+               if (ret < 0 && errno != EINTR && errno != EAGAIN) {
+                       perror("poll()");
+                       exit(1);
+               }
+       } while (ret <= 0);
+
+       exitpid = waitpid(-1, &exitstat, WNOHANG);
+       if (exitpid == 0)
+               /* child successfully went to main loop & closed socket */
+               exit(0);
+
+       /* child failed one way or another ... */
+       if (WIFEXITED(exitstat))
+               fprintf(stderr, "%s failed to start, exited %d\n", di->name,
+                       WEXITSTATUS(exitstat));
+       else if (WIFSIGNALED(exitstat))
+               fprintf(stderr, "%s crashed in startup, signal %d\n", di->name,
+                       WTERMSIG(exitstat));
+       else
+               fprintf(stderr, "%s failed to start, unknown problem\n",
+                       di->name);
+       exit(1);
+}
+
+static int daemon_ctl_sock = -1;
+
+static void frr_daemonize(void)
+{
+       int fds[2];
+       pid_t pid;
+
+       if (socketpair(AF_UNIX, SOCK_STREAM, 0, fds)) {
+               perror("socketpair() for daemon control");
+               exit(1);
+       }
+       set_cloexec(fds[0]);
+       set_cloexec(fds[1]);
+
+       pid = fork();
+       if (pid < 0) {
+               perror("fork()");
+               exit(1);
+       }
+       if (pid == 0) {
+               /* child */
+               close(fds[0]);
+               if (setsid() < 0) {
+                       perror("setsid()");
+                       exit(1);
+               }
+
+               daemon_ctl_sock = fds[1];
+               return;
+       }
+
+       close(fds[1]);
+       frr_daemon_wait(fds[0]);
+}
+
 void frr_config_fork(void)
 {
        hook_call(frr_late_init, master);
@@ -385,11 +460,8 @@ void frr_config_fork(void)
        if (di->dryrun)
                exit(0);
 
-       /* Daemonize. */
-       if (di->daemon_mode && daemon(0, 0) < 0) {
-               zlog_err("Zebra daemon failed: %s", strerror(errno));
-               exit(1);
-       }
+       if (di->daemon_mode)
+               frr_daemonize();
 
        if (!di->pid_file)
                di->pid_file = pidfile_default;
@@ -430,6 +502,11 @@ void frr_run(struct thread_master *master)
        zlog_notice("%s %s starting: %svty@%d%s", di->name, FRR_VERSION,
                    instanceinfo, di->vty_port, di->startinfo);
 
+       if (daemon_ctl_sock != -1) {
+               close(daemon_ctl_sock);
+               daemon_ctl_sock = -1;
+       }
+
        struct thread thread;
        while (thread_fetch(master, &thread))
                thread_call(&thread);