xfixes: Add ClientDisconnectMode

With Wayland compositors now being able to start Xwayland on demand, the
next logical step is to be able to stop Xwayland when there is no more
need for it.

The Xserver itself is capable of terminating itself once all X11 clients
are gone, yet in a typical full session, there are a number of X11
clients running continuously (e.g. the Xsettings daemon, IBus, etc.).

Those always-running clients will prevent the Xserver from terminating,
because the actual number of X11 clients will never drop to 0. Worse,
the X11 window manager of a Wayland compositor also counts as an X11
client, hence also preventing Xwayland from stopping.

Some compositors such as mutter use the XRes extension to query the X11
clients connected, match their PID with the actual executable name and
compare those with a list of executables that can be ignored when
deciding to kill the Xserver.

But that's not just clumsy, it is also racy, because a new X11 client
might initiate a connection the X11 server right when the compositor is
about to kill it.

To solve this issue directly at the Xserver level, this add new entries
to the XFixes extension to let the X11 clients themselves specify the
disconnect mode they expect.

Typically, those X11 daemon clients would specify the disconnect mode
XFixesClientDisconnectFlagTerminate to let the Xserver know that they
should not be accounted for when checking the remaining clients prior
to terminate.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>

5 files changed, 184 insertions, 5 deletions

diff --git a/xfixes/Makefile.am b/xfixes/Makefile.am
index 2a95c065b..52a7e6c6a 100644
--- a/xfixes/Makefile.am
+++ b/xfixes/Makefile.am
@@ -4,6 +4,7 @@ AM_CFLAGS = $(DIX_CFLAGS)
 
 libxfixes_la_SOURCES = 	\
 	cursor.c	\
+	disconnect.c	\
 	region.c	\
 	saveset.c	\
 	select.c	\
diff --git a/xfixes/disconnect.c b/xfixes/disconnect.c
new file mode 100644
index 000000000..77932725e
--- /dev/null
+++ b/xfixes/disconnect.c
@@ -0,0 +1,147 @@
+/*
+ * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
+ * Copyright 2010 Red Hat, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ *
+ * Copyright © 2002 Keith Packard
+ *
+ * Permission to use, copy, modify, distribute, and sell this software and its
+ * documentation for any purpose is hereby granted without fee, provided that
+ * the above copyright notice appear in all copies and that both that
+ * copyright notice and this permission notice appear in supporting
+ * documentation, and that the name of Keith Packard not be used in
+ * advertising or publicity pertaining to distribution of the software without
+ * specific, written prior permission.  Keith Packard makes no
+ * representations about the suitability of this software for any purpose.  It
+ * is provided "as is" without express or implied warranty.
+ *
+ * KEITH PACKARD DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+ * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
+ * EVENT SHALL KEITH PACKARD BE LIABLE FOR ANY SPECIAL, INDIRECT OR
+ * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
+ * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+ * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifdef HAVE_DIX_CONFIG_H
+#include <dix-config.h>
+#endif
+
+#include "xfixesint.h"
+#include "opaque.h"
+
+static DevPrivateKeyRec ClientDisconnectPrivateKeyRec;
+
+#define ClientDisconnectPrivateKey (&ClientDisconnectPrivateKeyRec)
+
+typedef struct _ClientDisconnect {
+    int disconnect_mode;
+} ClientDisconnectRec, *ClientDisconnectPtr;
+
+#define GetClientDisconnect(s) \
+    ((ClientDisconnectPtr) dixLookupPrivate(&(s)->devPrivates, \
+                                            ClientDisconnectPrivateKey))
+
+int
+ProcXFixesSetClientDisconnectMode(ClientPtr client)
+{
+    ClientDisconnectPtr pDisconnect = GetClientDisconnect(client);
+
+    REQUEST(xXFixesSetClientDisconnectModeReq);
+
+    pDisconnect->disconnect_mode = stuff->disconnect_mode;
+
+    return Success;
+}
+
+int _X_COLD
+SProcXFixesSetClientDisconnectMode(ClientPtr client)
+{
+    REQUEST(xXFixesSetClientDisconnectModeReq);
+
+    swaps(&stuff->length);
+
+    REQUEST_AT_LEAST_SIZE(xXFixesSetClientDisconnectModeReq);
+
+    swapl(&stuff->disconnect_mode);
+
+    return (*ProcXFixesVector[stuff->xfixesReqType]) (client);
+}
+
+int
+ProcXFixesGetClientDisconnectMode(ClientPtr client)
+{
+    ClientDisconnectPtr pDisconnect = GetClientDisconnect(client);
+    xXFixesGetClientDisconnectModeReply reply;
+
+    REQUEST_SIZE_MATCH(xXFixesGetClientDisconnectModeReq);
+
+    reply = (xXFixesGetClientDisconnectModeReply) {
+        .type = X_Reply,
+        .sequenceNumber = client->sequence,
+        .length = 0,
+        .disconnect_mode = pDisconnect->disconnect_mode,
+    };
+    if (client->swapped) {
+        swaps(&reply.sequenceNumber);
+        swapl(&reply.disconnect_mode);
+    }
+    WriteToClient(client, sizeof(xXFixesGetClientDisconnectModeReply), &reply);
+
+    return Success;
+}
+
+int _X_COLD
+SProcXFixesGetClientDisconnectMode(ClientPtr client)
+{
+    REQUEST(xXFixesGetClientDisconnectModeReq);
+
+    swaps(&stuff->length);
+
+    REQUEST_SIZE_MATCH(xXFixesGetClientDisconnectModeReq);
+
+    return (*ProcXFixesVector[stuff->xfixesReqType]) (client);
+}
+
+Bool
+XFixesShouldDisconnectClient(ClientPtr client)
+{
+    ClientDisconnectPtr pDisconnect = GetClientDisconnect(client);
+
+    if (!pDisconnect)
+        return FALSE;
+
+    if (dispatchExceptionAtReset & DE_TERMINATE)
+        return (pDisconnect->disconnect_mode & XFixesClientDisconnectFlagTerminate);
+
+    return FALSE;
+}
+
+Bool
+XFixesClientDisconnectInit(void)
+{
+    if (!dixRegisterPrivateKey(&ClientDisconnectPrivateKeyRec,
+                               PRIVATE_CLIENT, sizeof(ClientDisconnectRec)))
+        return FALSE;
+
+    return TRUE;
+}
diff --git a/xfixes/meson.build b/xfixes/meson.build
index 4ca819c8d..0e97d477b 100644
--- a/xfixes/meson.build
+++ b/xfixes/meson.build
@@ -1,5 +1,6 @@
 srcs_xfixes = [
     'cursor.c',
+    'disconnect.c',
     'region.c',
     'saveset.c',
     'select.c',
diff --git a/xfixes/xfixes.c b/xfixes/xfixes.c
index 53a6bd62f..4ea9171d9 100644
--- a/xfixes/xfixes.c
+++ b/xfixes/xfixes.c
@@ -1,6 +1,6 @@
 /*
  * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
- * Copyright 2010 Red Hat, Inc.
+ * Copyright 2010, 2021 Red Hat, Inc.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
@@ -103,6 +103,7 @@ static const int version_requests[] = {
     X_XFixesExpandRegion,       /* Version 3 */
     X_XFixesShowCursor,         /* Version 4 */
     X_XFixesDestroyPointerBarrier,      /* Version 5 */
+    X_XFixesGetClientDisconnectMode,    /* Version 6 */
 };
 
 int (*ProcXFixesVector[XFixesNumberRequests]) (ClientPtr) = {
@@ -139,7 +140,10 @@ int (*ProcXFixesVector[XFixesNumberRequests]) (ClientPtr) = {
 /*************** Version 4 ****************/
         ProcXFixesHideCursor, ProcXFixesShowCursor,
 /*************** Version 5 ****************/
-ProcXFixesCreatePointerBarrier, ProcXFixesDestroyPointerBarrier,};
+        ProcXFixesCreatePointerBarrier, ProcXFixesDestroyPointerBarrier,
+/*************** Version 6 ****************/
+        ProcXFixesSetClientDisconnectMode, ProcXFixesGetClientDisconnectMode,
+};
 
 static int
 ProcXFixesDispatch(ClientPtr client)
@@ -200,7 +204,10 @@ static int (*SProcXFixesVector[XFixesNumberRequests]) (ClientPtr) = {
 /*************** Version 4 ****************/
         SProcXFixesHideCursor, SProcXFixesShowCursor,
 /*************** Version 5 ****************/
-SProcXFixesCreatePointerBarrier, SProcXFixesDestroyPointerBarrier,};
+        SProcXFixesCreatePointerBarrier, SProcXFixesDestroyPointerBarrier,
+/*************** Version 6 ****************/
+        SProcXFixesSetClientDisconnectMode, SProcXFixesGetClientDisconnectMode,
+};
 
 static _X_COLD int
 SProcXFixesDispatch(ClientPtr client)
@@ -220,7 +227,10 @@ XFixesExtensionInit(void)
         (&XFixesClientPrivateKeyRec, PRIVATE_CLIENT, sizeof(XFixesClientRec)))
         return;
 
-    if (XFixesSelectionInit() && XFixesCursorInit() && XFixesRegionInit() &&
+    if (XFixesSelectionInit() &&
+        XFixesCursorInit() &&
+        XFixesRegionInit() &&
+        XFixesClientDisconnectInit() &&
         (extEntry = AddExtension(XFIXES_NAME, XFixesNumberEvents,
                                  XFixesNumberErrors,
                                  ProcXFixesDispatch, SProcXFixesDispatch,
diff --git a/xfixes/xfixesint.h b/xfixes/xfixesint.h
index 44e889040..f597354a0 100644
--- a/xfixes/xfixesint.h
+++ b/xfixes/xfixesint.h
@@ -1,6 +1,6 @@
 /*
  * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
- * Copyright 2010 Red Hat, Inc.
+ * Copyright 2010, 2021 Red Hat, Inc.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
@@ -290,6 +290,26 @@ int
 int
  SProcXFixesDestroyPointerBarrier(ClientPtr client);
 
+/* Version 6 */
+
+Bool
+ XFixesClientDisconnectInit(void);
+
+int
+ ProcXFixesSetClientDisconnectMode(ClientPtr client);
+
+int
+ ProcXFixesGetClientDisconnectMode(ClientPtr client);
+
+int
+ SProcXFixesSetClientDisconnectMode(ClientPtr client);
+
+int
+ SProcXFixesGetClientDisconnectMode(ClientPtr client);
+
+Bool
+ XFixesShouldDisconnectClient(ClientPtr client);
+
 /* Xinerama */
 #ifdef PANORAMIX
 extern int (*PanoramiXSaveXFixesVector[XFixesNumberRequests]) (ClientPtr);