[systemd-devel] [PATCH] logind: implement generic multi-session
David Herrmann
dh.herrmann at gmail.com
Tue Sep 17 14:40:19 PDT 2013
This enables the multi-session capability for seats that don't have VTs.
For legacy seats with VTs, everything stays the same. However, all other
seats now also get the multi-session capability.
The only feature that was missing was session-switching. As logind can
force a session-switch and signal that via the "Active" property, we only
need a way to allow synchronized/delayed session switches. Compositors
need to cleanup some devices before acknowledging the session switch.
Therefore, we use the session-devices to give compositors a chance to
block a session-switch until they cleaned everything up.
If you activate a session on a seat without VTs, we send a PauseDevice
signal to the active session for every active device. Only once the
session acknowledged all these with a PauseDeviceComplete() call, we
perform the final session switch.
One important note is that delayed session-switching is meant for
backwards compatibility. New compositors or other sessions should really
try to deal correctly with forced session switches! They only need to
handle EACCES/EPERM from syscalls and treat them as "PauseDevice" signal.
Following logind patches will add a timeout to session-switches which
forces the switch if the active session does not react in a timely
fashion. Moreover, explicit ForceActivate() calls might also be supported.
Hence, sessions must not crash if their devices get paused.
---
src/login/logind-seat.c | 15 +++++++++++++++
src/login/logind-seat.h | 2 ++
src/login/logind-session-device.c | 28 ++++++++++++++++++++++++++++
src/login/logind-session-device.h | 1 +
src/login/logind-session.c | 31 ++++++++++++++++++++++++++-----
5 files changed, 72 insertions(+), 5 deletions(-)
diff --git a/src/login/logind-seat.c b/src/login/logind-seat.c
index f88738a..4a4d40a 100644
--- a/src/login/logind-seat.c
+++ b/src/login/logind-seat.c
@@ -425,6 +425,21 @@ int seat_attach_session(Seat *s, Session *session) {
return 0;
}
+void seat_complete_switch(Seat *s) {
+ Session *session;
+
+ assert(s);
+
+ /* if no session-switch is pending or if it got canceled, do nothing */
+ if (!s->pending_switch)
+ return;
+
+ session = s->pending_switch;
+ s->pending_switch = NULL;
+
+ seat_set_active(s, session);
+}
+
bool seat_has_vts(Seat *s) {
assert(s);
diff --git a/src/login/logind-seat.h b/src/login/logind-seat.h
index d3438b8..be6db6e 100644
--- a/src/login/logind-seat.h
+++ b/src/login/logind-seat.h
@@ -38,6 +38,7 @@ struct Seat {
LIST_HEAD(Device, devices);
Session *active;
+ Session *pending_switch;
LIST_HEAD(Session, sessions);
bool in_gc_queue:1;
@@ -59,6 +60,7 @@ int seat_read_active_vt(Seat *s);
int seat_preallocate_vts(Seat *s);
int seat_attach_session(Seat *s, Session *session);
+void seat_complete_switch(Seat *s);
bool seat_has_vts(Seat *s);
bool seat_is_seat0(Seat *s);
diff --git a/src/login/logind-session-device.c b/src/login/logind-session-device.c
index 80fd364..e92bb54 100644
--- a/src/login/logind-session-device.c
+++ b/src/login/logind-session-device.c
@@ -414,10 +414,21 @@ void session_device_free(SessionDevice *sd) {
}
void session_device_complete_pause(SessionDevice *sd) {
+ SessionDevice *iter;
+ Iterator i;
+
if (!sd->active)
return;
session_device_stop(sd);
+
+ /* if not all devices are paused, wait for further completion events */
+ HASHMAP_FOREACH(iter, sd->session->devices, i)
+ if (iter->active)
+ return;
+
+ /* complete any pending session switch */
+ seat_complete_switch(sd->session->seat);
}
void session_device_resume_all(Session *s) {
@@ -449,3 +460,20 @@ void session_device_pause_all(Session *s) {
}
}
}
+
+unsigned int session_device_try_pause_all(Session *s) {
+ SessionDevice *sd;
+ Iterator i;
+ unsigned int num_pending = 0;
+
+ assert(s);
+
+ HASHMAP_FOREACH(sd, s->devices, i) {
+ if (sd->active) {
+ session_device_notify(sd, SESSION_DEVICE_TRY_PAUSE);
+ ++num_pending;
+ }
+ }
+
+ return num_pending;
+}
diff --git a/src/login/logind-session-device.h b/src/login/logind-session-device.h
index 511fce0..eac7ca7 100644
--- a/src/login/logind-session-device.h
+++ b/src/login/logind-session-device.h
@@ -57,3 +57,4 @@ void session_device_complete_pause(SessionDevice *sd);
void session_device_resume_all(Session *s);
void session_device_pause_all(Session *s);
+unsigned int session_device_try_pause_all(Session *s);
diff --git a/src/login/logind-session.c b/src/login/logind-session.c
index fcc1901..eea0bfb 100644
--- a/src/login/logind-session.c
+++ b/src/login/logind-session.c
@@ -100,6 +100,8 @@ void session_free(Session *s) {
if (s->seat) {
if (s->seat->active == s)
s->seat->active = NULL;
+ if (s->seat->pending_switch == s)
+ s->seat->pending_switch = NULL;
LIST_REMOVE(Session, sessions_by_seat, s->seat->sessions, s);
}
@@ -375,21 +377,40 @@ int session_load(Session *s) {
}
int session_activate(Session *s) {
+ unsigned int num_pending;
+
assert(s);
assert(s->user);
- if (s->vtnr <= 0)
- return -ENOTSUP;
-
if (!s->seat)
return -ENOTSUP;
if (s->seat->active == s)
return 0;
- assert(seat_has_vts(s->seat));
+ /* on seats with VTs, we let VTs manage session-switching */
+ if (seat_has_vts(s->seat)) {
+ if (s->vtnr <= 0)
+ return -ENOTSUP;
+
+ return chvt(s->vtnr);
+ }
- return chvt(s->vtnr);
+ /* On seats without VTs, we implement session-switching in logind. We
+ * try to pause all session-devices and wait until the session
+ * controller acknowledged them. Once all devices are asleep, we simply
+ * switch the active session and be done.
+ * We save the session we want to switch to in seat->pending_switch and
+ * seat_complete_switch() will perform the final switch. */
+
+ s->seat->pending_switch = s;
+
+ /* if no devices are running, immediately perform the session switch */
+ num_pending = session_device_try_pause_all(s);
+ if (!num_pending)
+ seat_complete_switch(s->seat);
+
+ return 0;
}
static int session_link_x11_socket(Session *s) {
--
1.8.4
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