logind: expose CanGraphical and CanTTY properties on seat objects

Since we boot so fast now that gdm might get started before the
graphics drivers are properly loaded and probed we might end up
announcing seat0 to gdm before it has graphics capabilities. Which will
cause gdm/X11 cause to fail later on.

To fix this race, let's expose CanGraphical and CanTTY fields on all
seats, which clarify whether a seat is suitable for gdm resp, suitable
for text logins. gdm then needs to watch CanGraphical and spawn X11 on
it only if it is true.

This way:

USB graphics seats will expose CanGraphical=yes, CanTTY=no

Machines with no graphics drivers at all, but a text console:
CanGraphical=no, CanTTY=yes

Machines with CONFIG_VT turned off: CanGraphical=yes, CanTTY=no

And the most important case: seat0 where the graphics driver has not
been probed yet boot up with CanGraphical=no, CanTTY=yes first, which
then changes to CanGraphical=yes as soon as the probing is complete.

4 files changed, 72 insertions, 7 deletions

diff --git a/src/login/logind-device.c b/src/login/logind-device.c
index 828e1efe4a..51b15358ba 100644
--- a/src/login/logind-device.c
+++ b/src/login/logind-device.c
@@ -65,22 +65,32 @@ void device_free(Device *d) {
 }
 
 void device_detach(Device *d) {
+        Seat *s;
         assert(d);
 
-        if (d->seat)
-                LIST_REMOVE(Device, devices, d->seat->devices, d);
+        if (!d->seat)
+                return;
 
-        seat_add_to_gc_queue(d->seat);
+        s = d->seat;
+        LIST_REMOVE(Device, devices, d->seat->devices, d);
         d->seat = NULL;
+
+        seat_add_to_gc_queue(s);
+        seat_send_changed(s, "CanGraphical\0");
 }
 
 void device_attach(Device *d, Seat *s) {
         assert(d);
         assert(s);
 
+        if (d->seat == s)
+                return;
+
         if (d->seat)
                 device_detach(d);
 
         d->seat = s;
         LIST_PREPEND(Device, devices, s->devices, d);
+
+        seat_send_changed(s, "CanGraphical\0");
 }
diff --git a/src/login/logind-seat-dbus.c b/src/login/logind-seat-dbus.c
index 4bf9bf7b1f..7833d70a03 100644
--- a/src/login/logind-seat-dbus.c
+++ b/src/login/logind-seat-dbus.c
@@ -36,6 +36,8 @@
         "  <property name=\"Id\" type=\"s\" access=\"read\"/>\n"        \
         "  <property name=\"ActiveSession\" type=\"so\" access=\"read\"/>\n" \
         "  <property name=\"CanMultiSession\" type=\"b\" access=\"read\"/>\n" \
+        "  <property name=\"CanTTY\" type=\"b\" access=\"read\"/>\n" \
+        "  <property name=\"CanGraphical\" type=\"b\" access=\"read\"/>\n" \
         "  <property name=\"Sessions\" type=\"a(so)\" access=\"read\"/>\n" \
         "  <property name=\"IdleHint\" type=\"b\" access=\"read\"/>\n"  \
         "  <property name=\"IdleSinceHint\" type=\"t\" access=\"read\"/>\n" \
@@ -133,7 +135,7 @@ static int bus_seat_append_sessions(DBusMessageIter *i, const char *property, vo
         return 0;
 }
 
-static int bus_seat_append_multi_session(DBusMessageIter *i, const char *property, void *data) {
+static int bus_seat_append_can_multi_session(DBusMessageIter *i, const char *property, void *data) {
         Seat *s = data;
         dbus_bool_t b;
 
@@ -149,6 +151,38 @@ static int bus_seat_append_multi_session(DBusMessageIter *i, const char *propert
         return 0;
 }
 
+static int bus_seat_append_can_tty(DBusMessageIter *i, const char *property, void *data) {
+        Seat *s = data;
+        dbus_bool_t b;
+
+        assert(i);
+        assert(property);
+        assert(s);
+
+        b = seat_can_tty(s);
+
+        if (!dbus_message_iter_append_basic(i, DBUS_TYPE_BOOLEAN, &b))
+                return -ENOMEM;
+
+        return 0;
+}
+
+static int bus_seat_append_can_graphical(DBusMessageIter *i, const char *property, void *data) {
+        Seat *s = data;
+        dbus_bool_t b;
+
+        assert(i);
+        assert(property);
+        assert(s);
+
+        b = seat_can_graphical(s);
+
+        if (!dbus_message_iter_append_basic(i, DBUS_TYPE_BOOLEAN, &b))
+                return -ENOMEM;
+
+        return 0;
+}
+
 static int bus_seat_append_idle_hint(DBusMessageIter *i, const char *property, void *data) {
         Seat *s = data;
         dbus_bool_t b;
@@ -210,7 +244,9 @@ static int get_seat_for_path(Manager *m, const char *path, Seat **_s) {
 static const BusProperty bus_login_seat_properties[] = {
         { "Id",                     bus_property_append_string,      "s", offsetof(Seat, id), true },
         { "ActiveSession",          bus_seat_append_active,       "(so)", 0 },
-        { "CanMultiSession",        bus_seat_append_multi_session,   "b", 0 },
+        { "CanMultiSession",        bus_seat_append_can_multi_session, "b", 0 },
+        { "CanTTY",                 bus_seat_append_can_tty,         "b", 0 },
+        { "CanGraphical",           bus_seat_append_can_graphical,   "b", 0 },
         { "Sessions",               bus_seat_append_sessions,    "a(so)", 0 },
         { "IdleHint",               bus_seat_append_idle_hint,       "b", 0 },
         { "IdleSinceHint",          bus_seat_append_idle_hint_since, "t", 0 },
diff --git a/src/login/logind-seat.c b/src/login/logind-seat.c
index 755f20c03a..045712192a 100644
--- a/src/login/logind-seat.c
+++ b/src/login/logind-seat.c
@@ -104,9 +104,13 @@ int seat_save(Seat *s) {
         fprintf(f,
                 "# This is private data. Do not parse.\n"
                 "IS_VTCONSOLE=%i\n"
-                "CAN_MULTI_SESSION=%i\n",
+                "CAN_MULTI_SESSION=%i\n"
+                "CAN_TTY=%i\n"
+                "CAN_GRAPHICAL=%i\n",
                 seat_is_vtconsole(s),
-                seat_can_multi_session(s));
+                seat_can_multi_session(s),
+                seat_can_tty(s),
+                seat_can_graphical(s));
 
         if (s->active) {
                 assert(s->active->user);
@@ -427,6 +431,18 @@ bool seat_can_multi_session(Seat *s) {
         return s->manager->console_active_fd >= 0;
 }
 
+bool seat_can_tty(Seat *s) {
+        assert(s);
+
+        return seat_is_vtconsole(s);
+}
+
+bool seat_can_graphical(Seat *s) {
+        assert(s);
+
+        return !!s->devices;
+}
+
 int seat_get_idle_hint(Seat *s, dual_timestamp *t) {
         Session *session;
         bool idle_hint = true;
diff --git a/src/login/logind-seat.h b/src/login/logind-seat.h
index d41320da46..1abbc344ec 100644
--- a/src/login/logind-seat.h
+++ b/src/login/logind-seat.h
@@ -63,6 +63,9 @@ int seat_attach_session(Seat *s, Session *session);
 
 bool seat_is_vtconsole(Seat *s);
 bool seat_can_multi_session(Seat *s);
+bool seat_can_tty(Seat *s);
+bool seat_can_graphical(Seat *s);
+
 int seat_get_idle_hint(Seat *s, dual_timestamp *t);
 
 int seat_start(Seat *s);