libweston/launcher: Allow VT switch without get_vt

get_vt is used to check if VTs are enabled, by verifying that a VT greater than
0 is returned.

libseat always implements switching, with switch to an active session
currently being a noop in all backends. libseat does not currently have
a get_vt implementation. Make get_vt errors more explicit, and allow VT
switching anyway if the error is ENOSYS.

Signed-off-by: Kenny Levinsen <kl@kl.wtf>

libweston/launcher-logind.c

@@ -860,6 +860,9 @@ static int
 launcher_logind_get_vt(struct weston_launcher *launcher)
 {
 	struct launcher_logind *wl = wl_container_of(launcher, wl, base);
+	if (wl->vtnr <= 0) {
+		return -EINVAL;
+	}
 	return wl->vtnr;
 }
 

libweston/launcher-util.c

@@ -31,6 +31,7 @@
 #include "launcher-util.h"
 #include "launcher-impl.h"
 
+#include <errno.h>
 #include <stdint.h>
 #include <unistd.h>
 #include <linux/input.h>
@@ -107,10 +108,12 @@ switch_vt_binding(struct weston_keyboard *keyboard,
 WL_EXPORT void
 weston_setup_vt_switch_bindings(struct weston_compositor *compositor)
 {
+	int ret;
 	uint32_t key;
 	struct weston_launcher *launcher = compositor->launcher;
 
-	if (launcher->iface->get_vt(launcher) <= 0)
+	ret = launcher->iface->get_vt(launcher);
+	if (ret < 0 && ret != -ENOSYS)
 		return;
 
 	if (compositor->vt_switching == false)