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.

6 files changed, 116 insertions, 19 deletions

diff --git a/src/login/logind-device.c b/src/login/logind-device.c
index 51b15358ba..2bcd6a10c5 100644
--- a/src/login/logind-device.c
+++ b/src/login/logind-device.c
@@ -25,7 +25,7 @@
 #include "logind-device.h"
 #include "util.h"
 
-Device* device_new(Manager *m, const char *sysfs) {
+Device* device_new(Manager *m, const char *sysfs, bool master) {
         Device *d;
 
         assert(m);
@@ -48,6 +48,7 @@ Device* device_new(Manager *m, const char *sysfs) {
         }
 
         d->manager = m;
+        d->master = master;
         dual_timestamp_get(&d->timestamp);
 
         return d;
@@ -75,11 +76,16 @@ void device_detach(Device *d) {
         LIST_REMOVE(Device, devices, d->seat->devices, d);
         d->seat = NULL;
 
-        seat_add_to_gc_queue(s);
-        seat_send_changed(s, "CanGraphical\0");
+        if (!seat_has_master_device(s)) {
+                seat_add_to_gc_queue(s);
+                seat_send_changed(s, "CanGraphical\0");
+        }
 }
 
 void device_attach(Device *d, Seat *s) {
+        Device *i;
+        bool had_master;
+
         assert(d);
         assert(s);
 
@@ -90,7 +96,26 @@ void device_attach(Device *d, Seat *s) {
                 device_detach(d);
 
         d->seat = s;
-        LIST_PREPEND(Device, devices, s->devices, d);
+        had_master = seat_has_master_device(s);
+
+        /* We keep the device list sorted by the "master" flag. That is, master
+         * devices are at the front, other devices at the tail. As there is no
+         * way to easily add devices at the list-tail, we need to iterate the
+         * list to find the first non-master device when adding non-master
+         * devices. We assume there is only a few (normally 1) master devices
+         * per seat, so we iterate only a few times. */
+
+        if (d->master || !s->devices)
+                LIST_PREPEND(Device, devices, s->devices, d);
+        else {
+                LIST_FOREACH(devices, i, s->devices) {
+                        if (!i->devices_next || !i->master) {
+                                LIST_INSERT_AFTER(Device, devices, s->devices, i, d);
+                                break;
+                        }
+                }
+        }
 
-        seat_send_changed(s, "CanGraphical\0");
+        if (!had_master && d->master)
+                seat_send_changed(s, "CanGraphical\0");
 }
diff --git a/src/login/logind-device.h b/src/login/logind-device.h
index 3b153568cb..315f0e66b0 100644
--- a/src/login/logind-device.h
+++ b/src/login/logind-device.h
@@ -33,13 +33,14 @@ struct Device {
 
         char *sysfs;
         Seat *seat;
+        bool master;
 
         dual_timestamp timestamp;
 
         LIST_FIELDS(struct Device, devices);
 };
 
-Device* device_new(Manager *m, const char *sysfs);
+Device* device_new(Manager *m, const char *sysfs, bool master);
 void device_free(Device *d);
 void device_attach(Device *d, Seat *s);
 void device_detach(Device *d);
diff --git a/src/login/logind-seat.c b/src/login/logind-seat.c
index 470d08bc05..2c60b8ae51 100644
--- a/src/login/logind-seat.c
+++ b/src/login/logind-seat.c
@@ -448,10 +448,17 @@ bool seat_can_tty(Seat *s) {
         return seat_is_vtconsole(s);
 }
 
+bool seat_has_master_device(Seat *s) {
+        assert(s);
+
+        /* device list is ordered by "master" flag */
+        return !!s->devices && s->devices->master;
+}
+
 bool seat_can_graphical(Seat *s) {
         assert(s);
 
-        return !!s->devices;
+        return seat_has_master_device(s);
 }
 
 int seat_get_idle_hint(Seat *s, dual_timestamp *t) {
@@ -499,7 +506,7 @@ int seat_check_gc(Seat *s, bool drop_not_started) {
         if (seat_is_vtconsole(s))
                 return 1;
 
-        return !!s->devices;
+        return seat_has_master_device(s);
 }
 
 void seat_add_to_gc_queue(Seat *s) {
diff --git a/src/login/logind-seat.h b/src/login/logind-seat.h
index c8ab17f7cf..bd5390f553 100644
--- a/src/login/logind-seat.h
+++ b/src/login/logind-seat.h
@@ -63,6 +63,7 @@ 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_has_master_device(Seat *s);
 bool seat_can_graphical(Seat *s);
 
 int seat_get_idle_hint(Seat *s, dual_timestamp *t);
diff --git a/src/login/logind.c b/src/login/logind.c
index 4ef92b8253..29019c214b 100644
--- a/src/login/logind.c
+++ b/src/login/logind.c
@@ -151,6 +151,8 @@ void manager_free(Manager *m) {
 
         if (m->udev_seat_monitor)
                 udev_monitor_unref(m->udev_seat_monitor);
+        if (m->udev_device_monitor)
+                udev_monitor_unref(m->udev_device_monitor);
         if (m->udev_vcsa_monitor)
                 udev_monitor_unref(m->udev_vcsa_monitor);
         if (m->udev_button_monitor)
@@ -184,7 +186,7 @@ void manager_free(Manager *m) {
         free(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) {
         Device *d;
 
         assert(m);
@@ -195,10 +197,13 @@ int manager_add_device(Manager *m, const char *sysfs, Device **_device) {
                 if (_device)
                         *_device = d;
 
+                /* we support adding master-flags, but not removing them */
+                d->master = d->master || master;
+
                 return 0;
         }
 
-        d = device_new(m, sysfs);
+        d = device_new(m, sysfs, master);
         if (!d)
                 return -ENOMEM;
 
@@ -373,7 +378,8 @@ int manager_process_seat_device(Manager *m, struct udev_device *d) {
 
         } else {
                 const char *sn;
-                Seat *seat;
+                Seat *seat = NULL;
+                bool master;
 
                 sn = udev_device_get_property_value(d, "ID_SEAT");
                 if (isempty(sn))
@@ -384,16 +390,23 @@ int manager_process_seat_device(Manager *m, struct udev_device *d) {
                         return 0;
                 }
 
-                r = manager_add_device(m, udev_device_get_syspath(d), &device);
+                /* ignore non-master devices for unknown seats */
+                master = udev_device_has_tag(d, "master-of-seat");
+                if (!master && !(seat = hashmap_get(m->seats, sn)))
+                        return 0;
+
+                r = manager_add_device(m, udev_device_get_syspath(d), master, &device);
                 if (r < 0)
                         return r;
 
-                r = manager_add_seat(m, sn, &seat);
-                if (r < 0) {
-                        if (!device->seat)
-                                device_free(device);
+                if (!seat) {
+                        r = manager_add_seat(m, sn, &seat);
+                        if (r < 0) {
+                                if (!device->seat)
+                                        device_free(device);
 
-                        return r;
+                                return r;
+                        }
                 }
 
                 device_attach(device, seat);
@@ -762,6 +775,22 @@ int manager_dispatch_seat_udev(Manager *m) {
         return r;
 }
 
+static int manager_dispatch_device_udev(Manager *m) {
+        struct udev_device *d;
+        int r;
+
+        assert(m);
+
+        d = udev_monitor_receive_device(m->udev_device_monitor);
+        if (!d)
+                return -ENOMEM;
+
+        r = manager_process_seat_device(m, d);
+        udev_device_unref(d);
+
+        return r;
+}
+
 int manager_dispatch_vcsa_udev(Manager *m) {
         struct udev_device *d;
         int r = 0;
@@ -1149,6 +1178,7 @@ static int manager_connect_udev(Manager *m) {
 
         assert(m);
         assert(!m->udev_seat_monitor);
+        assert(!m->udev_device_monitor);
         assert(!m->udev_vcsa_monitor);
         assert(!m->udev_button_monitor);
 
@@ -1169,6 +1199,33 @@ static int manager_connect_udev(Manager *m) {
         if (epoll_ctl(m->epoll_fd, EPOLL_CTL_ADD, m->udev_seat_fd, &ev) < 0)
                 return -errno;
 
+        m->udev_device_monitor = udev_monitor_new_from_netlink(m->udev, "udev");
+        if (!m->udev_device_monitor)
+                return -ENOMEM;
+
+        r = udev_monitor_filter_add_match_subsystem_devtype(m->udev_device_monitor, "input", NULL);
+        if (r < 0)
+                return r;
+
+        r = udev_monitor_filter_add_match_subsystem_devtype(m->udev_device_monitor, "graphics", NULL);
+        if (r < 0)
+                return r;
+
+        r = udev_monitor_filter_add_match_subsystem_devtype(m->udev_device_monitor, "drm", NULL);
+        if (r < 0)
+                return r;
+
+        r = udev_monitor_enable_receiving(m->udev_device_monitor);
+        if (r < 0)
+                return r;
+
+        m->udev_device_fd = udev_monitor_get_fd(m->udev_device_monitor);
+        zero(ev);
+        ev.events = EPOLLIN;
+        ev.data.u32 = FD_DEVICE_UDEV;
+        if (epoll_ctl(m->epoll_fd, EPOLL_CTL_ADD, m->udev_device_fd, &ev) < 0)
+                return -errno;
+
         /* Don't watch keys if nobody cares */
         if (m->handle_power_key != HANDLE_IGNORE ||
             m->handle_suspend_key != HANDLE_IGNORE ||
@@ -1545,6 +1602,10 @@ int manager_run(Manager *m) {
                         manager_dispatch_seat_udev(m);
                         break;
 
+                case FD_DEVICE_UDEV:
+                        manager_dispatch_device_udev(m);
+                        break;
+
                 case FD_VCSA_UDEV:
                         manager_dispatch_vcsa_udev(m);
                         break;
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);