logind: if we can't open /dev/tty0, assume there is no VT subsystem and don't pretend we could do VT switching

src/login/logind-dbus.c

@@ -301,7 +301,7 @@ static int bus_manager_create_session(Manager *m, DBusMessage *message, DBusMess
                 return -EINVAL;
 
         if (s) {
-                if (seat_is_vtconsole(s)) {
+                if (seat_can_multi_session(s)) {
                         if (vtnr <= 0 || vtnr > 63)
                                 return -EINVAL;
                 } else {

src/login/logind-seat-dbus.c

@@ -141,7 +141,7 @@ static int bus_seat_append_multi_session(DBusMessageIter *i, const char *propert
         assert(property);
         assert(s);
 
-        b = seat_is_vtconsole(s);
+        b = seat_can_multi_session(s);
 
         if (!dbus_message_iter_append_basic(i, DBUS_TYPE_BOOLEAN, &b))
                 return -ENOMEM;

src/login/logind-seat.c

@@ -101,8 +101,10 @@ int seat_save(Seat *s) {
 
         fprintf(f,
                 "# This is private data. Do not parse.\n"
-                "IS_VTCONSOLE=%i\n",
-                seat_is_vtconsole(s));
+                "IS_VTCONSOLE=%i\n"
+                "CAN_MULTI_SESSION=%i\n",
+                seat_is_vtconsole(s),
+                seat_can_multi_session(s));
 
         if (s->active) {
                 assert(s->active->user);
@@ -191,7 +193,7 @@ int seat_preallocate_vts(Seat *s) {
         if (s->manager->n_autovts <= 0)
                 return 0;
 
-        if (!seat_is_vtconsole(s))
+        if (!seat_can_multi_session(s))
                 return 0;
 
         for (i = 1; i <= s->manager->n_autovts; i++) {
@@ -266,7 +268,7 @@ int seat_active_vt_changed(Seat *s, int vtnr) {
         assert(s);
         assert(vtnr >= 1);
 
-        if (!seat_is_vtconsole(s))
+        if (!seat_can_multi_session(s))
                 return -EINVAL;
 
         log_debug("VT changed to %i", vtnr);
@@ -290,7 +292,7 @@ int seat_read_active_vt(Seat *s) {
 
         assert(s);
 
-        if (!seat_is_vtconsole(s))
+        if (!seat_can_multi_session(s))
                 return 0;
 
         lseek(s->manager->console_active_fd, SEEK_SET, 0);
@@ -388,7 +390,7 @@ int seat_attach_session(Seat *s, Session *session) {
         assert(session);
         assert(!session->seat);
 
-        if (!seat_is_vtconsole(s) && s->sessions)
+        if (!seat_can_multi_session(s) && s->sessions)
                 return -EEXIST;
 
         session->seat = s;
@@ -396,7 +398,7 @@ int seat_attach_session(Seat *s, Session *session) {
 
         seat_send_changed(s, "Sessions\0");
 
-        if (!seat_is_vtconsole(s)) {
+        if (!seat_can_multi_session(s)) {
                 assert(!s->active);
                 seat_set_active(s, session);
         }
@@ -410,6 +412,18 @@ bool seat_is_vtconsole(Seat *s) {
         return s->manager->vtconsole == s;
 }
 
+bool seat_can_multi_session(Seat *s) {
+        assert(s);
+
+        if (!seat_is_vtconsole(s))
+                return false;
+
+        /* If we can't watch which VT is in the foreground, we don't
+         * support VT switching */
+
+        return s->manager->console_active_fd >= 0;
+}
+
 int seat_get_idle_hint(Seat *s, dual_timestamp *t) {
         Session *session;
         bool idle_hint = true;

src/login/logind-seat.h

@@ -62,6 +62,7 @@ int seat_preallocate_vts(Seat *s);
 int seat_attach_session(Seat *s, Session *session);
 
 bool seat_is_vtconsole(Seat *s);
+bool seat_can_multi_session(Seat *s);
 int seat_get_idle_hint(Seat *s, dual_timestamp *t);
 
 int seat_start(Seat *s);

src/login/logind-session.c

@@ -185,7 +185,7 @@ int session_save(Session *s) {
                         "SERVICE=%s\n",
                         s->service);
 
-        if (s->seat && seat_is_vtconsole(s->seat))
+        if (s->seat && seat_can_multi_session(s->seat))
                 fprintf(f,
                         "VTNR=%i\n",
                         s->vtnr);
@@ -270,7 +270,7 @@ int session_load(Session *s) {
                         seat_attach_session(o, s);
         }
 
-        if (vtnr && s->seat && seat_is_vtconsole(s->seat)) {
+        if (vtnr && s->seat && seat_can_multi_session(s->seat)) {
                 int v;
 
                 k = safe_atoi(vtnr, &v);

src/login/logind.c

@@ -655,7 +655,6 @@ int manager_dispatch_seat_udev(Manager *m) {
         return r;
 }
 
-
 int manager_dispatch_vcsa_udev(Manager *m) {
         struct udev_device *d;
         int r = 0;
@@ -906,6 +905,12 @@ static int manager_connect_console(Manager *m) {
 
         m->console_active_fd = open("/sys/class/tty/tty0/active", O_RDONLY|O_NOCTTY|O_CLOEXEC);
         if (m->console_active_fd < 0) {
+
+                /* On certain architectures (S390 and Xen), /dev/tty0
+                   does not exist, so don't fail if we can't open it.*/
+                if (errno == ENOENT)
+                        return 0;
+
                 log_error("Failed to open /sys/class/tty/tty0/active: %m");
                 return -errno;
         }

src/login/sd-login.c

@@ -574,7 +574,7 @@ _public_ int sd_seat_can_multi_session(const char *seat) {
                 return -ENOMEM;
 
         r = parse_env_file(p, NEWLINE,
-                           "IS_VTCONSOLE", &s,
+                           "CAN_MULTI_SESSION", &s,
                            NULL);
         free(p);