MINOR: systemd wrapper: re-execute on SIGUSR2

Re-execute the systemd wrapper on SIGUSR2 and before reloading HAProxy,
making it possible to load a completely new version of HAProxy
(including a new version of the systemd wrapper) gracefully.
Since the wrapper accepts no command-line arguments of its own,
re-execution is signaled using the HAPROXY_SYSTEMD_REEXEC environment
variable.

This is primarily intended to help seamless upgrades of distribution
packages.

diff --git a/src/haproxy-systemd-wrapper.c b/src/haproxy-systemd-wrapper.c
index 8485dcd11da889cd91c3a94fa124c3d170882fb1..e373483d508587ff07300f7845e5d62c0eea685c 100644 (file)
--- a/src/haproxy-systemd-wrapper.c
+++ b/src/haproxy-systemd-wrapper.c
@@ -18,9 +18,11 @@
 #include <unistd.h>
 #include <sys/wait.h>
 
+#define REEXEC_FLAG "HAPROXY_SYSTEMD_REEXEC"
+
 static char *pid_file = "/run/haproxy.pid";
-static int main_argc;
-static char **main_argv;
+static int wrapper_argc;
+static char **wrapper_argv;
 
 static void locate_haproxy(char *buffer, size_t buffer_size)
 {
@@ -42,6 +44,11 @@ static void spawn_haproxy(char **pid_strv, int nb_pid)
 {
        char haproxy_bin[512];
        pid_t pid;
+       int main_argc;
+       char **main_argv;
+
+       main_argc = wrapper_argc - 1;
+       main_argv = wrapper_argv + 1;
 
        pid = fork();
        if (!pid) {
@@ -96,15 +103,10 @@ static int read_pids(char ***pid_strv)
 
 static void sigusr2_handler(int signum __attribute__((unused)))
 {
-       int i;
-       char **pid_strv = NULL;
-       int nb_pid = read_pids(&pid_strv);
+       setenv(REEXEC_FLAG, "1", 1);
+       printf("haproxy-systemd-wrapper: re-executing\n");
 
-       spawn_haproxy(pid_strv, nb_pid);
-
-       for (i = 0; i < nb_pid; ++i)
-               free(pid_strv[i]);
-       free(pid_strv);
+       execv(wrapper_argv[0], wrapper_argv);
 }
 
 static void sigint_handler(int signum __attribute__((unused)))
@@ -140,16 +142,40 @@ int main(int argc, char **argv)
 {
        int status;
 
-       --argc; ++argv;
-       main_argc = argc;
-       main_argv = argv;
+       wrapper_argc = argc;
+       wrapper_argv = argv;
 
+       --argc; ++argv;
        init(argc, argv);
 
        signal(SIGINT, &sigint_handler);
        signal(SIGUSR2, &sigusr2_handler);
 
-       spawn_haproxy(NULL, 0);
+       if (getenv(REEXEC_FLAG) != NULL) {
+               /* We are being re-executed: restart HAProxy gracefully */
+               int i;
+               char **pid_strv = NULL;
+               int nb_pid = read_pids(&pid_strv);
+               sigset_t sigs;
+
+               unsetenv(REEXEC_FLAG);
+               spawn_haproxy(pid_strv, nb_pid);
+
+               /* Unblock SIGUSR2 which was blocked by the signal handler
+                * before re-exec */
+               sigprocmask(SIG_BLOCK, NULL, &sigs);
+               sigdelset(&sigs, SIGUSR2);
+               sigprocmask(SIG_SETMASK, &sigs, NULL);
+
+               for (i = 0; i < nb_pid; ++i)
+                       free(pid_strv[i]);
+               free(pid_strv);
+       }
+       else {
+               /* Start a fresh copy of HAProxy */
+               spawn_haproxy(NULL, 0);
+       }
+
        status = -1;
        while (-1 != wait(&status) || errno == EINTR)
                ;