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Simplify the way we handler session-controllers and fix several
shortcomings:
* send ReleaseDevice() signals on forced session takeover
* fix mem-leaks for busnames in case VT preparation fails (non-critical)
* avoid passing pre-allocated names to helpers
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Our bus-name watch helpers only remove a bus-name if it's not a
controller, anymore. If we call manager_drop_busname() before
unregistering the controller, the busname will not be dropped. Therefore,
first drop the controller, then drop the bus-name.
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On request of Stef Walter.
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sd-event does not allow multiple handlers for a single signal. However,
logind sets up signal handlers for each session with VT_PROCESS set (that
is, it has an active controller). Therefore, registering multiple such
controllers will fail.
Lets make the VT-handler global, as it's mostly trivial, anyway. This way,
the sessions don't have to take care of that and we can simply acknowledge
all VT-switch requests as we always did.
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If controllers can expect logind to have "prepared" the VT (e.g. set it to
graphics mode, etc) then TakeControl() should fail if said preparation
failed (and session_restore_vt() was called).
(David: fixed up !CONFIG_VT case and errno-numbers)
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Better be safe than sorry...
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When we dropped support for creating a per-user to the "main" X11
display we stopped returning useful data in the "Display" user property.
With this change this is fixed and we again expose an appropriate
(graphical session) in the property that is useful as the "main" one, if
one is needed.
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No functional change expected :)
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This function is no longer just about muteing the VT. We do all kinds of
VT setup for sessions using the controller-API. Rename the function to
something more appropriate.
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The tty associated with a VT should be owned by the owner of the session
running on the VT. This is important for supporting a socket activated X
server, since the X server will open the tty itself.
This commit makes sure to chown the tty any time a session is
created and and chown it back to root any time the session
is removed. This behavior is copied from /bin/login.
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Add Mir to the list of session types. This is implemented for LightDM
in lp:~robert-ancell/lightdm/xdg-session-desktop [1].
[1] https://code.launchpad.net/~robert-ancell/lightdm/xdg-session-desktop/+merge/214108
(david: adjusted commit-header and fixed whitespace issues)
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CLOCK_BOOTTIME_ALARM, too
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safe_close() automatically becomes a NOP when a negative fd is passed,
and returns -1 unconditionally. This makes it easy to write lines like
this:
fd = safe_close(fd);
Which will close an fd if it is open, and reset the fd variable
correctly.
By making use of this new scheme we can drop a > 200 lines of code that
was required to test for non-negative fds or to reset the closed fd
variable afterwards.
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Bring some arrays that are used for DEFINE_STRING_TABLE_LOOKUP() in the
same order than the enums they reference.
Also, pass the corresponding _MAX value to the array initalizer where
appropriate.
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utf8 needs to be initialized to NULL for the free for the early return,
otherwise we try to free invalid data.
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first (or second)
Previously the returned object of constructor functions where sometimes
returned as last, sometimes as first and sometimes as second parameter.
Let's clean this up a bit. Here are the new rules:
1. The object the new object is derived from is put first, if there is any
2. The object we are creating will be returned in the next arguments
3. This is followed by any additional arguments
Rationale:
For functions that operate on an object we always put that object first.
Constructors should probably not be too different in this regard. Also,
if the additional parameters might want to use varargs which suggests to
put them last.
Note that this new scheme only applies to constructor functions, not to
all other functions. We do give a lot of freedom for those.
Note that this commit only changes the order of the new functions we
added, for old ones we accept the wrong order and leave it like that.
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If -flto is used then gcc will generate a lot more warnings than before,
among them a number of use-without-initialization warnings. Most of them
without are false positives, but let's make them go away, because it
doesn't really matter.
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At login there is a small race window where session_get_state() will
return SESSION_ACTIVE instead of SESSION_OPENING. This must be fixed
since during that time there are calls to session_save() to save
session states and we want to write the correct state.
When we queue the start scope and service jobs, we wait for both of them
to finish before calling and continue processing in:
"session_jobs_reply() => session_send_create_reply()"
to create the session fifo and notify clients.
However, in the match_job_removed() D-Bus signal, we may hit situations
where the scope job has successfully finished and we are still waiting
for the user service job to finish. During that time the
"session->scope_job" will be freed and set to NULL, this makes
session_get_state() return SESSION_ACTIVE before it is really active, it
should return SESSION_OPENING since we are still waiting for the service
job to finish in order to create the session fifo.
To fix this, we also check if the session fifo fd was created, if so then
the session has entered the SESSION_ACTIVE state, if not then it is still
in the SESSION_OPENING state and it is waiting for the scope and service
jobs to finish.
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KillUserProcesses=yes/no should be ignored when termination is
explicitly requested.
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systemd-user-sessions.service
This way at shutdown we can be sure that the sessions go away before the
network.
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Simplify the shutdown logic a bit:
- Keep the session FIFO around in the PAM module, even after the session
shutdown hook has been finished. This allows logind to track precisely
when the PAM handler goes away.
- In the ReleaseSession() call start a timer, that will stop terminate
the session when elapsed.
- Never fiddle with the KillMode of scopes to configure whether user
processes should be killed or not. Instead, simply leave the scope
units around when we terminate a session whose processes should not be
killed.
- When killing is enabled, stop the session scope on FIFO EOF or after
the ReleaseSession() timeout. When killing is disabled, simply tell
PID 1 to abandon the scope.
Because the scopes stay around and hence all processes are always member
of a scope, the system shutdown logic should be more robust, as the
scopes can be shutdown as part of the usual shutdown logic.
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Use PID_FMT/USEC_FMT/... in more places.
Also update logind error messages to print the full path to a file that
failed. This should make debugging easier for people who do not know
off the top of their head where logind stores it state.
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This is initialized from XDG_SESSION_DESKTOP and is useful for GNOME
to recognize its own sessions. It's supposed to be set to a short string
identifying the session, such as "kde" or "gnome".
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logind has no concept of session ordering. Sessions have a unique name,
some attributes about the capabilities and that's already it. There is
currently no stable+total order on sessions. If we use the logind API to
switch between sessions, we are faced with an unordered list of sessions
we have no clue of.
This used to be no problem on seats with VTs or on seats with only a
single active session. However, with the introduction of multi-session
capability for seats without VTs, we need to find a way to order sessions
in a stable way.
This patch introduces session "positions". A position is a simple integer
assigned to a session which is never changed implicitly (currently, we
also don't change it explicitly, but that may be changed someday). For
seats with VTs, we force the position to be the same as the VTnr. Without
VTs, we simply find the lowest unassigned number and use it as position.
If position-assignment fails or if, for any reason, we decide to not
assign a position to a session, the position is set to 0 (which is treated
as invalid position).
During session_load() or if two sessions have the same VTnr, we may end up
with two sessions with the same position (this shouldn't happen, but lets
be fail-safe in case some other part of the stack fails). This case is
dealt with gracefully by ignoring any session but the first session
assigned to the position. Thus, session->pos is a hint, seat->positions[i]
is the definite position-assignment. Always verify both match in case you
need to modify them!
Additionally, we introduce SwitchTo(unsigned int) on the seat-dbus-API.
You can call it with any integer value != 0 and logind will try to switch
to the request position. If you implement a compositor or any other
session-controller, you simply watch for ctrl+alt+F1 to F12 and call
SwitchTo(Fx). logind will figure a way out deal with this number.
For convenience, we also introduce SwitchToNext/Previous(). It should be
called on ctrl+alt+Left/Right (like the kernel-console used to support).
Note that the public API (SwitchTo*()) is *not* bound to the underlying
logic that is implemented now. We don't export "session-positions" on the
dbus/C API! They are an implementation detail. Instead, the SwitchTo*()
API is supposed to be a hint to let logind choose the session-switching
logic. Any foreground session-controller is free to enumerate/order
existing sessions according to their needs and call Session.Activate()
manually. But the SwitchTo*() API provides a uniform behavior across
session-controllers.
Background: Session-switching keys depend on the active keymap. The XKB
specification provides the XKB_KEY_XF86Switch_VT_1-12 key-symbols which
have to be mapped by all keymaps to allow session-switching. It is usually
bound to ctrl+alt+Fx but may be set differently. A compositor passes any
keyboard input to XKB before passing it to clients. In case a key-press
invokes the XKB_KEY_XF86Switch_VT_x action, the keypress is *not*
forwarded to clients, but instead a session-switch is scheduled.
This actually prevents us from handling these keys outside of the session.
If an active compositor has a keymap with a different mapping of these
keys, and logind itself tries to catch these combinations, we end up with
the key-press sent to the compositor's clients *and* handled by logind.
This is *bad* and we must avoid this. The only situation where a
background process is allowed to handle key-presses is debugging and
emergency-keys. In these cases, we don't care for keymap mismatches and
accept the double-event. Another exception is unmapped keys like
PowerOff/Suspend (even though this one is controversial).
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X11 never made use of it anyway and it's probably better to just push
$DISPLAY into the systemd daemon from gnome-session (or equivalent
program) than to change libX11 to look for this socket. In particular
since we won't need this for Wayland anyway and we shouldn't add
infrastructure for stuff that's on its way out anyway.
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SipHash appears to be the new gold standard for hashing smaller strings
for hashtables these days, so let's make use of it.
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The only problem is that libgen.h #defines basename to point to it's
own broken implementation instead of the GNU one. This can be fixed
by #undefining basename.
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This field is always false, drop it. If you want a reliable way to get
session state, call session_get_state(). Testing for any flags directly
doesn't work currently so don't pretend it would.
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Sessions on seat0 must pass us a vtnr, otherwise, you shouldn't try
attaching it to seat0. For seats without VTs, we do the exact opposite: we
forbid VTs.
There can be odd situations if the session-files contain invalid
combinations. However, we try to keep sessions alive and restore state as
good as possible.
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Fix the whole code to use "unsigned int" for vtnr. 0 is an invalid vtnr so
we don't need negative numbers at all.
Note that most code already assumes it's unsigned so in case there's a
negative vtnr, our code may, under special circumstances, silently break.
So this patch makes sure all sources of vtnrs verify the validity. Also
note that the dbus api already uses unsigned ints.
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If a session process calls TakeControl(), we now put the VT into
KD_GRAPHICS+K_OFF mode. This way, the new session controller can solely
rely on the logind-dbus API to manage the session.
Once the controller exits or calls ReleaseControl(), we restore the VT. We
also restore it, if we lost a controller during crash/restart (but only if
there really *was* a controller previously).
Note that we also must put the VT into VT_PROCESS mode. We want VT_AUTO
semantics, but VT_AUTO+KD_GRAPHICS actually disables *all* VT switches
(who came up with that great idea?). Hence, we set VT_PROCESS for logind
but acknowledge *all* requests immediately.
If a compositor wants custom VT setups, they can still get this by *first*
calling TakeControl() and afterwards setting up the VT. logind doesn't
touch the VT during controller runtime, only during setup/teardown. This
is actually what weston already does.
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We now save the unique bus-name of a session-controller as CONTROLLER=%s
in the session files. This allows us to restore the controller after a
crash or restart.
Note that we test whether the name is still valid (dbus guarantees that
the name is unique as long as the machine is up and running). If it is,
we know that the controller still exists and can safely restore it. Our
dbus-name-tracking guarantees that we're notified once it exits.
Also note that session-devices are *not* restored. We have no way to know
which devices where used before the crash. We could store all these on
disk, too, or mark them via udev. However, this seems to be rather
cumbersome. Instead, we expect controllers to listen for NewSession
signals for their own session. This is sent on session_load() and they can
then re-request all devices.
The only race I could find is if logind crashes, then the session
controller tries calling ReleaseControl() (which will fail as logind is
down) but keeps the bus-connection valid for other independent requests.
If logind is restarted, it will restore the old controller and thus block
the session.
However, this seems unlikely for several reasons:
- The ReleaseControl() call must occur exactly in the timespan where
logind is dead.
- A process which calls ReleaseControl() usually closes the
bus-connection afterwards. Especially if ReleaseControl() fails, the
process should notice that something is wrong and close the bus.
- A process calling ReleaseControl() usually exits afterwards. There may
be any cleanup pending, but other than that, usual compositors exit.
- If a session-controller calls ReleaseControl(), a session is usually
considered closing. There is no known use-case where we hand-over
session-control in a single session. So we don't care whether the
controller is locked afterwards.
So this seems negligible.
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This patch converts PID 1 to libsystemd-bus and thus drops the
dependency on libdbus. The only remaining code using libdbus is a test
case that validates our bus marshalling against libdbus' marshalling,
and this dependency can be turned off.
This patch also adds a couple of things to libsystem-bus, that are
necessary to make the port work:
- Synthesizing of "Disconnected" messages when bus connections are
severed.
- Support for attaching multiple vtables for the same interface on the
same path.
This patch also fixes the SetDefaultTarget() and GetDefaultTarget() bus
calls which used an inappropriate signature.
As a side effect we will now generate PropertiesChanged messages which
carry property contents, rather than just invalidation information.
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each invocation
We can determine the list entry type via the typeof() gcc construct, and
so we should to make the macros much shorter to use.
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clang FTW!
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Unfortunately on ARM-32 systems dev_t can be 64bit and thus we cannot
store it easily in void* keys for hashtables. Fix that by passing a
pointer to the dev_t variable instead.
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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.
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A session-device is a device that is bound to a seat and used by a
session-controller to run the session. This currently includes DRM, fbdev
and evdev devices. A session-device can be created via RequestDevice() on
the dbus API of the session. You can drop it via ReleaseDevice() again.
Once the session is destroyed or you drop control of the session, all
session-devices are automatically destroyed.
Session devices follow the session "active" state. A device can be
active/running or inactive/paused. Whenever a session is not the active
session, no session-device of it can be active. That is, if a session is
not in foreground, all session-devices are paused.
Whenever a session becomes active, all devices are resumed/activated by
logind. If it fails, a device may stay paused.
With every session-device you request, you also get a file-descriptor
back. logind keeps a copy of this fd and uses kernel specific calls to
pause/resume the file-descriptors. For example, a DRM fd is muted
by logind as long as a given session is not active. Hence, the fd of the
application is also muted. Once the session gets active, logind unmutes
the fd and the application will get DRM access again.
This, however, requires kernel support. DRM devices provide DRM-Master for
synchronization, evdev devices have EVIOCREVOKE (pending on
linux-input-ML). fbdev devices do not provide such synchronization methods
(and never will).
Note that for evdev devices, we call EVIOCREVOKE once a session gets
inactive. However, this cannot be undone (the fd is still valid but mostly
unusable). So we reopen a new fd once the session is activated and send it
together with the ResumeDevice() signal.
With this infrastructure in place, compositors can now run without
CAP_SYS_ADMIN (that is, without being root). They use RequestControl() to
acquire a session and listen for devices via udev_monitor. For every
device they want to open, they call RequestDevice() on logind. This
returns a fd which they can use now. They no longer have to open the
devices themselves or call any privileged ioctls. This is all done by
logind.
Session-switches are still bound to VTs. Hence, compositors will get
notified via the usual VT mechanisms and can cleanup their state. Once the
VT switch is acknowledged as usual, logind will get notified via sysfs and
pause the old-session's devices and resume the devices of the new session.
To allow using this infrastructure with systems without VTs, we provide
notification signals. logind sends PauseDevice("force") dbus signals to
the current session controller for every device that it pauses. And it
sends ResumeDevice signals for every device that it resumes. For
seats with VTs this is sent _after_ the VT switch is acknowledged. Because
the compositor already acknowledged that it cleaned-up all devices.
However, for seats without VTs, this is used to notify the active
compositor that the session is about to be deactivated. That is, logind
sends PauseDevice("force") for each active device and then performs the
session-switch. The session-switch changes the "Active" property of the
session which can be monitored by the compositor. The new session is
activated and the ResumeDevice events are sent.
For seats without VTs, this is a forced session-switch. As this is not
backwards-compatible (xserver actually crashes, weston drops the related
devices, ..) we also provide an acknowledged session-switch. Note that
this is never used for sessions with VTs. You use the acknowledged
VT-switch on these seats.
An acknowledged session switch sends PauseDevice("pause") instead of
PauseDevice("force") to the active session. It schedules a short timeout
and waits for the session to acknowledge each of them with
PauseDeviceComplete(). Once all are acknowledged, or the session ran out
of time, a PauseDevice("force") is sent for all remaining active devices
and the session switch is performed.
Note that this is only partially implemented, yet, as we don't allow
multi-session without VTs, yet. A follow up commit will hook it up and
implemented the acknowledgements+timeout.
The implementation is quite simple. We use major/minor exclusively to
identify devices on the bus. On RequestDevice() we retrieve the
udev_device from the major/minor and search for an existing "Device"
object. If no exists, we create it. This guarantees us that we are
notified whenever the device changes seats or is removed.
We create a new SessionDevice object and link it to the related Session
and Device. Session->devices is a hashtable to lookup SessionDevice
objects via major/minor. Device->session_devices is a linked list so we
can release all linked session-devices once a device vanishes.
Now we only have to hook this up in seat_set_active() so we correctly
change device states during session-switches. As mentioned earlier, these
are forced state-changes as VTs are currently used exclusively for
multi-session implementations.
Everything else are hooks to release all session-devices once the
controller changes or a session is closed or removed.
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We currently use seat_can_multi_session() to test for two things:
* whether the seat can handle session-switching
* whether the seat has VTs
As both are currently logically equivalent, we didn't care. However, we
want to allow session-switching on seats without VTs, so split this helper
into:
* seat_can_multi_session(): whether session-switching is supported
* seat_has_vts(): whether the seat has VTs
Note that only one seat on a system can have VTs. There is only one set of
them. We automatically assign them to seat0 as usual.
With this patch in place, we can easily add new session-switching/tracking
methods without breaking any VT code as it is now protected by has_vts(),
no longer by can_multi_session().
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VT numbers start with 1. If a session has vtnr == 0, we must not assume it
is running on a VT.
Note that this could trigger the assert() below as CreateSession() sets
vtnr to 0, not <0.
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The seat->vtconsole member always points to the default seat seat0. Even
if VTs are disabled, it's used as default seat. Therefore, rename it to
seat0 to correctly state what it is.
This also changes the seat files in /run from IS_VTCONSOLE to IS_SEAT0. It
wasn't used by any code, yet, so this seems fine.
While we are at it, we also remove every "if (s->vtconsole)" as this
pointer is always valid!
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Currently, Activate() calls chvt(), which does an ioctl(VT_ACTIVATE) and
immediately calls seat_set_active(). However, VTs are allowed to prevent
being deactivated. Therefore, logind cannot be sure the VT_ACTIVATE call
was actually successful.
Furthermore, compositors often need to clean up their devices before they
acknowledge the VT switch. The immediate call to seat_set_active() may
modify underlying ACLs, though. Thus, some compositors may fail cleaning
up their stuff. Moreover, the compositor being switched to (if listening
to logind instead of VTs) will not be able to activate its devices if the
old VT still has them active.
We could simply add an VT_WAITACTIVE call, which blocks until the given VT
is active. However, this can block forever if the compositor hangs.
So to fix this, we make Activate() lazy. That is, it only schedules a
session-switch but does not wait for it to complete. The caller can no
longer rely on it being immediate. Instead, a caller is required to wait
for the PropertiesChanged signal and read the "Active" field.
We could make Activate() wait asynchronously for the session-switch to
complete and then send the return-message afterwards. However, this would
add a lot of state-tracking with no real gain:
1) Sessions normally don't care whether Activate() was actually
successful as they currently _must_ wait for the VT activation to do
anything for real.
2) Error messages for failed session switches can be printed by logind
instead of the session issuing Activate().
3) Sessions that require synchronous Activate() calls can simply issue
the call and then wait for "Active" properties to change. This also
allows them to implement their own timeout.
This change prepares for multi-session on seats without VTs. Forced VT
switches are always bad as compositors cannot perform any cleanup. This
isn't strictly required, but may lead to loss of information and ambiguous
error messages.
So for multi-session on seats without VTs, we must wait for the current
session to clean-up before finalizing the session-switch. This requires
Activate() to be lazy as we cannot block here.
Note that we can always implement a timeout which allows us to guarantee
the session switch to happen. Nevertheless, this calls for a lazy
Activate().
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A session usually has only a single compositor or other application that
controls graphics and input devices on it. To avoid multiple applications
from hijacking each other's devices or even using the devices in parallel,
we add session controllers.
A session controller is an application that manages a session. Specific
API calls may be limited to controllers to avoid others from getting
unprivileged access to restricted resources. A session becomes a
controller by calling the RequestControl() dbus API call. It can drop it
via ReleaseControl().
logind tracks bus-names to release the controller once an application
closes the bus. We use the new bus-name tracking to do that. Note that
during ReleaseControl() we need to check whether some other session also
tracks the name before we remove it from the bus-name tracking list.
Currently, we only allow one controller at a time. However, the public API
does not enforce this restriction. So if it makes sense, we can allow
multiple controllers in parallel later. Or we can add a "scope" parameter,
which allows a different controller for graphics-devices, sound-devices
and whatever you want.
Note that currently you get -EBUSY if there is already a controller. You
can force the RequestControl() call (root-only) to drop the current
controller and recover the session during an emergency. To recover a seat,
this is not needed, though. You can simply create a new session or
force-activate it.
To become a session controller, a dbus caller must either be root or the
same user as the user of the session. This allows us to run a session
compositor as user and we no longer need any CAP_SYS_ADMIN.
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Only ASCII letters and digits are allowed.
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