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-rw-r--r--util/oslib-posix.c71
1 files changed, 71 insertions, 0 deletions
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index a0fcdc2..4024918 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -490,3 +490,74 @@ int qemu_read_password(char *buf, int buf_size)
printf("\n");
return ret;
}
+
+
+pid_t qemu_fork(Error **errp)
+{
+ sigset_t oldmask, newmask;
+ struct sigaction sig_action;
+ int saved_errno;
+ pid_t pid;
+
+ /*
+ * Need to block signals now, so that child process can safely
+ * kill off caller's signal handlers without a race.
+ */
+ sigfillset(&newmask);
+ if (pthread_sigmask(SIG_SETMASK, &newmask, &oldmask) != 0) {
+ error_setg_errno(errp, errno,
+ "cannot block signals");
+ return -1;
+ }
+
+ pid = fork();
+ saved_errno = errno;
+
+ if (pid < 0) {
+ /* attempt to restore signal mask, but ignore failure, to
+ * avoid obscuring the fork failure */
+ (void)pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
+ error_setg_errno(errp, saved_errno,
+ "cannot fork child process");
+ errno = saved_errno;
+ return -1;
+ } else if (pid) {
+ /* parent process */
+
+ /* Restore our original signal mask now that the child is
+ * safely running. Only documented failures are EFAULT (not
+ * possible, since we are using just-grabbed mask) or EINVAL
+ * (not possible, since we are using correct arguments). */
+ (void)pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
+ } else {
+ /* child process */
+ size_t i;
+
+ /* Clear out all signal handlers from parent so nothing
+ * unexpected can happen in our child once we unblock
+ * signals */
+ sig_action.sa_handler = SIG_DFL;
+ sig_action.sa_flags = 0;
+ sigemptyset(&sig_action.sa_mask);
+
+ for (i = 1; i < NSIG; i++) {
+ /* Only possible errors are EFAULT or EINVAL The former
+ * won't happen, the latter we expect, so no need to check
+ * return value */
+ (void)sigaction(i, &sig_action, NULL);
+ }
+
+ /* Unmask all signals in child, since we've no idea what the
+ * caller's done with their signal mask and don't want to
+ * propagate that to children */
+ sigemptyset(&newmask);
+ if (pthread_sigmask(SIG_SETMASK, &newmask, NULL) != 0) {
+ Error *local_err = NULL;
+ error_setg_errno(&local_err, errno,
+ "cannot unblock signals");
+ error_report_err(local_err);
+ _exit(1);
+ }
+ }
+ return pid;
+}
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