1 files changed, 61 insertions, 39 deletions

diff --git a/iostat_process.c b/iostat_process.c
index d8766e0..9f98077 100644
--- a/iostat_process.c
+++ b/iostat_process.c
@@ -14,6 +14,12 @@ static time_t iostat_last_fail;
 static struct mog_iostat *iostat;
 static time_t iostat_fail_timeout = 10;
 
+enum mog_exerr {
+        MOG_EXERR_DUP2 = 3,
+        MOG_EXERR_SIGPROCMASK = 4,
+        MOG_EXERR_EXECVE = 5
+};
+
 static void iostat_atexit(void)
 {
         if (iostat_pid > 0)
@@ -40,8 +46,7 @@ static int iostat_pipe_init(int *fds)
         return 0;
 }
 
-/* only called in the child process */
-static const char * exec_cmd(const char *cmd)
+static const char *exec_cmd(const char *cmd)
 {
         time_t last_fail = time(NULL) - iostat_last_fail;
         time_t delay = iostat_fail_timeout - last_fail;
@@ -55,7 +60,7 @@ static const char * exec_cmd(const char *cmd)
         return xasprintf("sleep %d; exec %s", (int)delay, cmd);
 }
 
-static void dup2_or_die(int oldfd, int newfd, const char *errdesc)
+static int dup2_retry(int oldfd, int newfd) /* vfork-safe */
 {
         int rc;
 
@@ -63,57 +68,62 @@ static void dup2_or_die(int oldfd, int newfd, const char *errdesc)
                 rc = dup2(oldfd, newfd);
         while (rc < 0 && (errno == EINTR || errno == EBUSY));
 
-        if (rc < 0) {
-                syslog(LOG_CRIT, "dup2(%s) failed: %m", errdesc);
-                _exit(1);
-        }
+        return rc;
 }
 
-static void preexec_redirect(int out_fd)
+static void execve_iostat(int out_fd, const char *cmd) /* vfork-safe */
 {
-        int null_fd;
-
-        dup2_or_die(out_fd, STDOUT_FILENO, "iostat_pipe[1],STDOUT");
-        mog_close(out_fd);
-
-        null_fd = open("/dev/null", O_RDONLY);
-        if (null_fd < 0) {
-                syslog(LOG_CRIT, "open(/dev/null) failed: %m");
-                abort();
-        }
-        dup2_or_die(null_fd, STDIN_FILENO, "/dev/null,STDIN");
-        mog_close(null_fd);
-
-        /* don't touch stderr */
+        int i;
+        union {
+                char *argv[4];
+                char const *in[4];
+        } u;
+
+        u.in[0] = "/bin/sh";
+        u.in[1] = "-c";
+        u.in[2] = cmd;
+        u.in[3] = 0;
+
+        if (dup2_retry(out_fd, STDOUT_FILENO) < 0)
+                _exit(MOG_EXERR_DUP2);
+        if (!mog_cloexec_atomic)
+                mog_cloexec_from(STDERR_FILENO + 1);
+
+        /* ignore errors, not much we can do about missing signals */
+        for (i = 1; i < NSIG; i++)
+                (void)signal(i, SIG_DFL);
+
+        if (sigprocmask(SIG_SETMASK, &mog_emptyset, NULL) != 0)
+                _exit(MOG_EXERR_SIGPROCMASK);
+
+        execve("/bin/sh", u.argv, environ);
+        _exit(MOG_EXERR_EXECVE);
 }
 
 static pid_t iostat_fork_exec(int out_fd)
 {
         /* rely on /bin/sh to parse iostat command-line args */
         const char *cmd = getenv("MOG_IOSTAT_CMD");
+        int cs;
+
         if (!cmd)
                 cmd = "iostat -dx 1 30";
 
         cmd = exec_cmd(cmd);
-
+        CHECK(int, 0, pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs));
         iostat_pid = mog_fork_for_exec();
-        if (iostat_pid < 0) {
+        if (iostat_pid < 0)
                 syslog(LOG_ERR, "fork() for iostat failed: %m");
-        } else if (iostat_pid > 0) {
+        else if (iostat_pid == 0) /* child */
+                execve_iostat(out_fd, cmd);
+
+        /* parent */
+        CHECK(int, 0, pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, 0));
+        if (iostat_pid > 0)
                 mog_process_register(iostat_pid, MOG_PROC_IOSTAT);
-                mog_close(out_fd);
-        } else {
-                /* child */
-                preexec_redirect(out_fd);
-                if (! mog_cloexec_atomic)
-                        mog_cloexec_from(STDERR_FILENO + 1);
-
-                mog_intr_enable();
-                execl("/bin/sh", "sh", "-c", cmd, (char *)NULL);
-                syslog(LOG_CRIT, "execl(%s) failed: %m", cmd);
-                _exit(1);
-        }
+        mog_close(out_fd);
         mog_free(cmd);
+
         return iostat_pid;
 }
 
@@ -122,8 +132,20 @@ bool mog_iostat_respawn(int oldstatus)
         int fds[2];
         struct mog_fd *mfd;
 
-        if (WIFEXITED(oldstatus) && WEXITSTATUS(oldstatus) == 0) {
-                /* syslog(LOG_DEBUG, "iostat done, restarting"); */
+        if (WIFEXITED(oldstatus)) {
+                int ex = WEXITSTATUS(oldstatus);
+                const char *fn = 0;
+
+                switch (ex) {
+                case 0: break;
+                case MOG_EXERR_DUP2: fn = "dup2"; break;
+                case MOG_EXERR_SIGPROCMASK: fn = "sigprocmask"; break;
+                case MOG_EXERR_EXECVE: fn = "execve"; break;
+                default: fn = "(unknown)";
+                }
+                if (fn)
+                        syslog(LOG_ERR, "iostat exited due to %s failure", fn);
+                /* else syslog(LOG_DEBUG, "iostat done, restarting"); */
         } else {
                 iostat_last_fail = time(NULL);
                 syslog(LOG_WARNING,