qemu-ga: guest-shutdown: use only async-signal-safe functions

POSIX mandates[1] that a child process of a multi-thread program uses
only async-signal-safe functions before exec(). We consider qemu-ga
to be multi-thread, because it uses glib.

However, qmp_guest_shutdown() uses functions that are not
async-signal-safe. Fix it the following way:

- fclose() -> reopen_fd_to_null()
- execl() -> execle()
- exit() -> _exit()
- drop slog() usage (which is not safe)

  [1] http://pubs.opengroup.org/onlinepubs/009695399/functions/fork.html

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

1 files changed, 8 insertions, 11 deletions

diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index 68da71f..7664be1 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -37,8 +37,8 @@
 void qmp_guest_shutdown(bool has_mode, const char *mode, Error **err)
 {
     const char *shutdown_flag;
-    int ret, status;
     pid_t rpid, pid;
+    int status;
 
     slog("guest-shutdown called, mode: %s", mode);
     if (!has_mode || strcmp(mode, "powerdown") == 0) {
@@ -57,16 +57,13 @@ void qmp_guest_shutdown(bool has_mode, const char *mode, Error **err)
     if (pid == 0) {
         /* child, start the shutdown */
         setsid();
-        fclose(stdin);
-        fclose(stdout);
-        fclose(stderr);
-
-        ret = execl("/sbin/shutdown", "shutdown", shutdown_flag, "+0",
-                    "hypervisor initiated shutdown", (char*)NULL);
-        if (ret) {
-            slog("guest-shutdown failed: %s", strerror(errno));
-        }
-        exit(!!ret);
+        reopen_fd_to_null(0);
+        reopen_fd_to_null(1);
+        reopen_fd_to_null(2);
+
+        execle("/sbin/shutdown", "shutdown", shutdown_flag, "+0",
+               "hypervisor initiated shutdown", (char*)NULL, environ);
+        _exit(EXIT_FAILURE);
     } else if (pid < 0) {
         goto exit_err;
     }