seccomp: check TSYNC host capability

Remove -sandbox option if the host is not capable of TSYNC, since the
sandbox will fail at setup time otherwise. This will help libvirt, for
ex, to figure out if -sandbox will work.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Eduardo Otubo <otubo@redhat.com>
Acked-by: Eduardo Otubo <otubo@redhat.com>

qemu-seccomp.c

@@ -282,7 +282,24 @@ static QemuOptsList qemu_sandbox_opts = {
 
 static void seccomp_register(void)
 {
-    qemu_add_opts(&qemu_sandbox_opts);
+    bool add = false;
+
+    /* FIXME: use seccomp_api_get() >= 2 check when released */
+
+#if defined(SECCOMP_FILTER_FLAG_TSYNC)
+    int check;
+
+    /* check host TSYNC capability, it returns errno == ENOSYS if unavailable */
+    check = qemu_seccomp(SECCOMP_SET_MODE_FILTER,
+                         SECCOMP_FILTER_FLAG_TSYNC, NULL);
+    if (check < 0 && errno == EFAULT) {
+        add = true;
+    }
+#endif
+
+    if (add) {
+        qemu_add_opts(&qemu_sandbox_opts);
+    }
 }
 opts_init(seccomp_register);
 #endif

vl.c

@@ -4007,8 +4007,8 @@ int main(int argc, char **argv, char **envp)
     }
 
 #ifdef CONFIG_SECCOMP
-    if (qemu_opts_foreach(qemu_find_opts("sandbox"),
-                          parse_sandbox, NULL, NULL)) {
+    olist = qemu_find_opts_err("sandbox", NULL);
+    if (olist && qemu_opts_foreach(olist, parse_sandbox, NULL, NULL)) {
         exit(1);
     }
 #endif