logind: listen actively for session devices

Session compositors need access to fbdev, DRM and evdev devices if they
control a session. To make logind pass them to sessions, we need to
listen for them actively.

However, we avoid creating new seats for non master-of-seat devices. Only
once a seat is created, we start remembering all other session devices. If
the last master-device is removed (even if there are other non-master
devices still available), we destroy the seat. This is the current
behavior, but we need to explicitly implement it now as there may be
non-master devices in the seat->devices list.

Unlike master devices, we don't care whether our list of non-master
devices is complete. We don't export this list but use it only as cache if
sessions request these devices. Hence, if a session requests a device that
is not in the list, we will simply look it up. However, once a session
requested a device, we must be notified of "remove" udev events. So we
must link the devices somehow into the device-list.

Regarding the implementation, we now sort the device list by the "master"
flag. This guarantees that master devices are at the front and non-master
devices at the tail of the list. Thus, we can easily test whether a seat
has a master device attached.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/login/logind.h b/src/login/logind.h
index e9838a8afd..1a97351fff 100644
--- a/src/login/logind.h
+++ b/src/login/logind.h
@@ -57,9 +57,10 @@ struct Manager {
         LIST_HEAD(User, user_gc_queue);
 
         struct udev *udev;
-        struct udev_monitor *udev_seat_monitor, *udev_vcsa_monitor, *udev_button_monitor;
+        struct udev_monitor *udev_seat_monitor, *udev_device_monitor, *udev_vcsa_monitor, *udev_button_monitor;
 
         int udev_seat_fd;
+        int udev_device_fd;
         int udev_vcsa_fd;
         int udev_button_fd;
 
@@ -121,6 +122,7 @@ struct Manager {
 
 enum {
         FD_SEAT_UDEV,
+        FD_DEVICE_UDEV,
         FD_VCSA_UDEV,
         FD_BUTTON_UDEV,
         FD_CONSOLE,
@@ -132,7 +134,7 @@ enum {
 Manager *manager_new(void);
 void manager_free(Manager *m);
 
-int manager_add_device(Manager *m, const char *sysfs, Device **_device);
+int manager_add_device(Manager *m, const char *sysfs, bool master, Device **_device);
 int manager_add_button(Manager *m, const char *name, Button **_button);
 int manager_add_seat(Manager *m, const char *id, Seat **_seat);
 int manager_add_session(Manager *m, const char *id, Session **_session);