1 files changed, 71 insertions, 0 deletions
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index 892d2d8ad2..914cef5c2c 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -470,3 +470,74 @@ 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;
+}