login: add multi-session X wrapper

In preparation for https://bugzilla.gnome.org/show_bug.cgi?id=655380 we
decided it's better to include the multi-seat X wrapper in systemd,
rather than gdm. (Side effect: this makes this accessible for other
DMs)

This is a stop-gap for now, until X gins proper multi-seat graphics
support at which point this code will go away without replacement.

.gitignore

@@ -1,3 +1,4 @@
+/systemd-multi-seat-x
 /systemd-cgtop
 /systemd-coredump
 /systemd-cat

Makefile.am

@@ -99,6 +99,7 @@ AM_CPPFLAGS = \
 	-DUSER_GENERATOR_PATH=\"$(usergeneratordir)\" \
 	-DSYSTEM_SHUTDOWN_PATH=\"$(systemshutdowndir)\" \
 	-DSYSTEMD_KBD_MODEL_MAP=\"$(pkgdatadir)/kbd-model-map\" \
+        -DX_SERVER=\"$(bindir)/X\" \
 	-I $(top_srcdir)/src \
 	-I $(top_srcdir)/src/readahead \
 	-I $(top_srcdir)/src/login \
@@ -1988,6 +1989,20 @@ logind-install-data-hook:
 INSTALL_DATA_HOOKS += \
 	logind-install-data-hook
 
+systemd_multi_seat_x_SOURCES = \
+	src/login/multi-seat-x.c
+
+systemd_multi_seat_x_CFLAGS = \
+	$(AM_CFLAGS) \
+	$(UDEV_CFLAGS)
+
+systemd_multi_seat_x_LDADD = \
+	libsystemd-basic.la \
+	$(UDEV_LIBS)
+
+rootlibexec_PROGRAMS += \
+	systemd-multi-seat-x
+
 systemd_uaccess_SOURCES = \
 	src/login/uaccess.c
 

src/login/multi-seat-x.c

@@ -0,0 +1,187 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2011 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU General Public License as published by
+  the Free Software Foundation; either version 2 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <string.h>
+#include <unistd.h>
+
+#include <libudev.h>
+
+#include "util.h"
+
+int main(int argc, char *argv[]) {
+
+        struct udev *udev = NULL;
+        struct udev_enumerate *enumerator = NULL;
+        struct udev_list_entry *first, *item;
+        int i;
+        const char *seat = NULL;
+        char **new_argv;
+        char *path = NULL, *device_node = NULL;
+        int r;
+        FILE *f = NULL;
+
+        /* This binary will go away as soon as X natively supports
+         * display enumeration with udev in a way that covers both PCI
+         * and USB. */
+
+        /* This will simply determine the fb device id of the graphics
+         * device assigned to a seat and write a configuration file
+         * from it and then spawn the real X server. */
+
+        for (i = 1; i < argc; i++)
+                if (streq(argv[i], "-seat"))
+                        seat = argv[i+1];
+
+        if (isempty(seat) || streq(seat, "seat0")) {
+                argv[0] = (char*) X_SERVER;
+                execv(X_SERVER, argv);
+                log_error("Failed to execute real X server: %m");
+                goto fail;
+        }
+
+        udev = udev_new();
+        if (!udev) {
+                log_error("Failed to allocate udev environment.");
+                goto fail;
+        }
+
+        enumerator = udev_enumerate_new(udev);
+        if (!enumerator) {
+                log_error("Failed to allocate udev enumerator.");
+                goto fail;
+        }
+
+        udev_enumerate_add_match_subsystem(enumerator, "graphics");
+        udev_enumerate_add_match_tag(enumerator, seat);
+
+        r = udev_enumerate_scan_devices(enumerator);
+        if (r < 0) {
+                log_error("Failed to enumerate devices.");
+                goto fail;
+        }
+
+        first = udev_enumerate_get_list_entry(enumerator);
+        udev_list_entry_foreach(item, first) {
+                struct udev_device *d;
+                const char *dn;
+
+                d = udev_device_new_from_syspath(udev, udev_list_entry_get_name(item));
+                if (!d)
+                        continue;
+
+                dn = udev_device_get_devnode(d);
+
+                if (!dn) {
+                        device_node = strdup(dn);
+                        if (!device_node) {
+                                udev_device_unref(d);
+                                log_error("Out of memory.");
+                                goto fail;
+                        }
+                }
+
+                udev_device_unref(d);
+
+                if (device_node)
+                        break;
+        }
+
+        if (!device_node) {
+                log_error("Failed to find device node for seat %s.", seat);
+                goto fail;
+        }
+
+        r = safe_mkdir("/run/systemd/multi-session-x", 0755, 0, 0);
+        if (r < 0) {
+                log_error("Failed to create directory: %s", strerror(-r));
+                goto fail;
+        }
+
+        path = strappend("/run/systemd/multi-session-x/", seat);
+        if (!path) {
+                log_error("Out of memory");
+                goto fail;
+        }
+
+        f = fopen(path, "we");
+        if (!f) {
+                log_error("Failed to write configuration file: %m");
+                goto fail;
+        }
+
+        fprintf(f,
+                "Section \"Device\"\n"
+                "        Identifier \"udev\"\n"
+                "        Driver \"fbdev\"\n"
+                "        Option \"fbdev\" \"%s\"\n"
+                "EndSection\n"
+                "Section \"ServerFlags\"\n"
+                "        Option \"AutoAddDevices\" \"True\"\n"
+                "        Option \"AllowEmptyInput\" \"True\"\n"
+                "EndSection\n",
+                device_node);
+
+        fflush(f);
+
+        if (ferror(f)) {
+                log_error("Failed to write configuration file: %m");
+                goto fail;
+        }
+
+        fclose(f);
+        f = NULL;
+
+        new_argv = alloca(sizeof(char*) * (argc + 3 + 1));
+        memcpy(new_argv, argv, sizeof(char*) * (argc + 2 + 1));
+
+        new_argv[0] = (char*) X_SERVER;
+        new_argv[argc+0] = (char*) "-config";
+        new_argv[argc+1] = path;
+        new_argv[argc+2] = (char*) "-sharevts";
+        new_argv[argc+3] = NULL;
+
+        udev_enumerate_unref(enumerator);
+        enumerator = NULL;
+
+        udev_unref(udev);
+        udev = NULL;
+
+        free(device_node);
+        device_node = NULL;
+
+        execv(X_SERVER, new_argv);
+        log_error("Failed to execute real X server: %m");
+
+fail:
+        if (enumerator)
+                udev_enumerate_unref(enumerator);
+
+        if (udev)
+                udev_unref(udev);
+
+        free(path);
+        free(device_node);
+
+        if (f)
+                fclose(f);
+
+        return EXIT_FAILURE;
+}