Howdy,
The following patch improves the -pidfile a fair bit. -pidfile isn't
terribly usable at the moment with -daemonize as the wrong pid gets
written to the file.
Furthermore, there's a race in -pidfile between the stat() and initial
create. For a management tool, there's no 100% reliable way to know
whether there's a stale pidfile or whether another QEMU process is running.
The attached patch uses a common technique for dealing with pidfiles.
An advisory lock is taken once the pidfile is opened. The nice thing
about advisory locks is that the file is unlocked if a process dies.
This allows for a truly atomic pidfile to be implemented.
AFAIK, lockf() exists on Windows. I do not know if it works as one
would expect though.
Regards,
Anthony Liguori
diff -r 58621c427a39 vl.c
--- a/vl.c Sat Mar 03 21:06:59 2007 -0600
+++ b/vl.c Sat Mar 03 21:15:21 2007 -0600
@@ -4387,44 +4387,24 @@ void usb_info(void)
}
}
-/***********************************************************/
-/* pid file */
-
-static char *pid_filename;
-
-/* Remove PID file. Called on normal exit */
-
-static void remove_pidfile(void)
-{
- unlink (pid_filename);
-}
-
-static void create_pidfile(const char *filename)
-{
- struct stat pidstat;
- FILE *f;
-
- /* Try to write our PID to the named file */
- if (stat(filename, &pidstat) < 0) {
- if (errno == ENOENT) {
- if ((f = fopen (filename, "w")) == NULL) {
- perror("Opening pidfile");
- exit(1);
- }
- fprintf(f, "%d\n", getpid());
- fclose(f);
- pid_filename = qemu_strdup(filename);
- if (!pid_filename) {
- fprintf(stderr, "Could not save PID filename");
- exit(1);
- }
- atexit(remove_pidfile);
- }
- } else {
- fprintf(stderr, "%s already exists. Remove it and try again.\n",
- filename);
- exit(1);
- }
+static int create_pidfile(const char *filename)
+{
+ int fd;
+ char buffer[128];
+ int len;
+
+ fd = open(filename, O_RDWR | O_CREAT, 0600);
+ if (fd == -1)
+ return -1;
+
+ if (lockf(fd, F_TLOCK, 0) == -1)
+ return -1;
+
+ len = snprintf(buffer, sizeof(buffer), "%ld\n", (long)getpid());
+ if (write(fd, buffer, len) != len)
+ return -1;
+
+ return 0;
}
/***********************************************************/
@@ -6874,6 +6854,7 @@ int main(int argc, char **argv)
char usb_devices[MAX_USB_CMDLINE][128];
int usb_devices_index;
int fds[2];
+ const char *pid_file = NULL;
LIST_INIT (&vm_change_state_head);
#ifndef _WIN32
@@ -7263,7 +7244,7 @@ int main(int argc, char **argv)
break;
#endif
case QEMU_OPTION_pidfile:
- create_pidfile(optarg);
+ pid_file = optarg;
break;
#ifdef TARGET_I386
case QEMU_OPTION_win2k_hack:
@@ -7353,9 +7334,12 @@ int main(int argc, char **argv)
if (len == -1 && (errno == EINTR))
goto again;
- if (len != 1 || status != 0)
+ if (len != 1)
exit(1);
- else
+ else if (status == 1) {
+ fprintf(stderr, "Could not acquire pidfile\n");
+ exit(1);
+ } else
exit(0);
} else if (pid < 0)
exit(1);
@@ -7376,6 +7360,15 @@ int main(int argc, char **argv)
signal(SIGTTIN, SIG_IGN);
}
#endif
+
+ if (pid_file && create_pidfile(pid_file) != 0) {
+ if (daemonize) {
+ uint8_t status = 1;
+ write(fds[1], &status, 1);
+ } else
+ fprintf(stderr, "Could not acquire pid file\n");
+ exit(1);
+ }
#ifdef USE_KQEMU
if (smp_cpus > 1)
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