logind: introduce session-devices

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.

1 files changed, 451 insertions, 0 deletions

diff --git a/src/login/logind-session-device.c b/src/login/logind-session-device.c
new file mode 100644
index 0000000000..80fd364139
--- /dev/null
+++ b/src/login/logind-session-device.c
@@ -0,0 +1,451 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2013 David Herrmann
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 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
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <assert.h>
+#include <fcntl.h>
+#include <libudev.h>
+#include <linux/input.h>
+#include <linux/ioctl.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "dbus-common.h"
+#include "logind-session-device.h"
+#include "util.h"
+#include "missing.h"
+
+enum SessionDeviceNotifications {
+        SESSION_DEVICE_RESUME,
+        SESSION_DEVICE_TRY_PAUSE,
+        SESSION_DEVICE_PAUSE,
+        SESSION_DEVICE_RELEASE,
+};
+
+static void session_device_notify(SessionDevice *sd, enum SessionDeviceNotifications type) {
+        _cleanup_dbus_message_unref_ DBusMessage *m = NULL;
+        _cleanup_free_ char *path = NULL;
+        const char *t = NULL;
+
+        assert(sd);
+
+        if (!sd->session->controller)
+                return;
+
+        path = session_bus_path(sd->session);
+        if (!path)
+                return;
+
+        m = dbus_message_new_signal(path,
+                                    "org.freedesktop.login1.Session",
+                                    (type == SESSION_DEVICE_RESUME) ? "ResumeDevice" : "PauseDevice");
+        if (!m)
+                return;
+
+        if (!dbus_message_set_destination(m, sd->session->controller))
+                return;
+
+        switch (type) {
+        case SESSION_DEVICE_RESUME:
+                if (!dbus_message_append_args(m,
+                                              DBUS_TYPE_UINT32, major(sd->dev),
+                                              DBUS_TYPE_UINT32, minor(sd->dev),
+                                              DBUS_TYPE_UNIX_FD, &sd->fd,
+                                              DBUS_TYPE_INVALID))
+                        return;
+                break;
+        case SESSION_DEVICE_TRY_PAUSE:
+                t = "pause";
+                break;
+        case SESSION_DEVICE_PAUSE:
+                t = "force";
+                break;
+        case SESSION_DEVICE_RELEASE:
+                t = "gone";
+                break;
+        default:
+                return;
+        }
+
+        if (t && !dbus_message_append_args(m,
+                                           DBUS_TYPE_UINT32, major(sd->dev),
+                                           DBUS_TYPE_UINT32, minor(sd->dev),
+                                           DBUS_TYPE_STRING, &t,
+                                           DBUS_TYPE_INVALID))
+                return;
+
+        dbus_connection_send(sd->session->manager->bus, m, NULL);
+}
+
+static int sd_eviocrevoke(int fd) {
+        static bool warned;
+        int r;
+
+        assert(fd >= 0);
+
+        r = ioctl(fd, EVIOCREVOKE, 1);
+        if (r < 0) {
+                r = -errno;
+                if (r == -EINVAL && !warned) {
+                        warned = true;
+                        log_warning("kernel does not support evdev-revocation");
+                }
+        }
+
+        return 0;
+}
+
+static int sd_drmsetmaster(int fd) {
+        int r;
+
+        assert(fd >= 0);
+
+        r = ioctl(fd, DRM_IOCTL_SET_MASTER, 0);
+        if (r < 0)
+                return -errno;
+
+        return 0;
+}
+
+static int sd_drmdropmaster(int fd) {
+        int r;
+
+        assert(fd >= 0);
+
+        r = ioctl(fd, DRM_IOCTL_DROP_MASTER, 0);
+        if (r < 0)
+                return -errno;
+
+        return 0;
+}
+
+static int session_device_open(SessionDevice *sd, bool active) {
+        int fd;
+
+        assert(sd->type != DEVICE_TYPE_UNKNOWN);
+
+        /* open device and try to get an udev_device from it */
+        fd = open(sd->node, O_RDWR|O_CLOEXEC|O_NOCTTY|O_NONBLOCK);
+        if (fd < 0)
+                return -errno;
+
+        switch (sd->type) {
+        case DEVICE_TYPE_DRM:
+                if (active)
+                        sd_drmsetmaster(fd);
+                else {
+                        /* DRM-Master is granted to the first user who opens a
+                         * device automatically (ughh, racy!). Hence, we just
+                         * drop DRM-Master in case we were the first. */
+                        sd_drmdropmaster(fd);
+                }
+                break;
+        case DEVICE_TYPE_EVDEV:
+                if (!active)
+                        sd_eviocrevoke(fd);
+                break;
+        case DEVICE_TYPE_FBDEV:
+        case DEVICE_TYPE_UNKNOWN:
+        default:
+                /* fallback for devices wihout synchronizations */
+                break;
+        }
+
+        return fd;
+}
+
+static int session_device_start(SessionDevice *sd) {
+        int r;
+
+        assert(sd);
+        assert(session_is_active(sd->session));
+
+        if (sd->active)
+                return 0;
+
+        switch (sd->type) {
+        case DEVICE_TYPE_DRM:
+                /* Device is kept open. Simply call drmSetMaster() and hope
+                 * there is no-one else. In case it fails, we keep the device
+                 * paused. Maybe at some point we have a drmStealMaster(). */
+                r = sd_drmsetmaster(sd->fd);
+                if (r < 0)
+                        return r;
+                break;
+        case DEVICE_TYPE_EVDEV:
+                /* Evdev devices are revoked while inactive. Reopen it and we
+                 * are fine. */
+                r = session_device_open(sd, true);
+                if (r < 0)
+                        return r;
+                close_nointr_nofail(sd->fd);
+                sd->fd = r;
+                break;
+        case DEVICE_TYPE_FBDEV:
+                /* fbdev devices have no way to synchronize access. Moreover,
+                 * they mostly operate through mmaps() without any pageflips
+                 * and modesetting, so there is no way for us to prevent access
+                 * but tear down mmaps.
+                 * That would be quite expensive to do on a per-fd context. So
+                 * ignore legcy fbdev and let its users feel the pain they asked
+                 * for when deciding for fbdev. */
+        case DEVICE_TYPE_UNKNOWN:
+        default:
+                /* fallback for devices wihout synchronizations */
+                break;
+        }
+
+        sd->active = true;
+        return 0;
+}
+
+static void session_device_stop(SessionDevice *sd) {
+        assert(sd);
+
+        if (!sd->active)
+                return;
+
+        switch (sd->type) {
+        case DEVICE_TYPE_DRM:
+                /* On DRM devices we simply drop DRM-Master but keep it open.
+                 * This allows the user to keep resources allocated. The
+                 * CAP_SYS_ADMIN restriction to DRM-Master prevents users from
+                 * circumventing this. */
+                sd_drmdropmaster(sd->fd);
+                break;
+        case DEVICE_TYPE_EVDEV:
+                /* Revoke access on evdev file-descriptors during deactivation.
+                 * This will basically prevent any operations on the fd and
+                 * cannot be undone. Good side is: it needs no CAP_SYS_ADMIN
+                 * protection this way. */
+                sd_eviocrevoke(sd->fd);
+                break;
+        case DEVICE_TYPE_FBDEV:
+        case DEVICE_TYPE_UNKNOWN:
+        default:
+                /* fallback for devices without synchronization */
+                break;
+        }
+
+        sd->active = false;
+}
+
+static DeviceType detect_device_type(struct udev_device *dev) {
+        const char *sysname, *subsystem;
+        DeviceType type;
+
+        sysname = udev_device_get_sysname(dev);
+        subsystem = udev_device_get_subsystem(dev);
+        type = DEVICE_TYPE_UNKNOWN;
+
+        if (streq_ptr(subsystem, "graphics")) {
+                if (!streq(sysname, "fbcon") && startswith(sysname, "fb"))
+                        type = DEVICE_TYPE_FBDEV;
+        } else if (streq_ptr(subsystem, "drm")) {
+                if (startswith(sysname, "card"))
+                        type = DEVICE_TYPE_DRM;
+        } else if (streq_ptr(subsystem, "input")) {
+                if (startswith(sysname, "event"))
+                        type = DEVICE_TYPE_EVDEV;
+        }
+
+        return type;
+}
+
+static int session_device_verify(SessionDevice *sd) {
+        struct udev_device *dev, *p = NULL;
+        const char *sp, *node;
+        int r;
+
+        dev = udev_device_new_from_devnum(sd->session->manager->udev, 'c', sd->dev);
+        if (!dev)
+                return -ENODEV;
+
+        sp = udev_device_get_syspath(dev);
+        node = udev_device_get_devnode(dev);
+        if (!node) {
+                r = -EINVAL;
+                goto err_dev;
+        }
+
+        /* detect device type so we can find the correct sysfs parent */
+        sd->type = detect_device_type(dev);
+        if (sd->type == DEVICE_TYPE_UNKNOWN) {
+                r = -ENODEV;
+                goto err_dev;
+        } else if (sd->type == DEVICE_TYPE_EVDEV) {
+                /* for evdev devices we need the parent node as device */
+                p = dev;
+                dev = udev_device_get_parent_with_subsystem_devtype(p, "input", NULL);
+                if (!dev) {
+                        r = -ENODEV;
+                        goto err_dev;
+                }
+                sp = udev_device_get_syspath(dev);
+        } else if (sd->type != DEVICE_TYPE_FBDEV &&
+                   sd->type != DEVICE_TYPE_DRM) {
+                /* Prevent opening unsupported devices. Especially devices of
+                 * subsystem "input" must be opened via the evdev node as
+                 * we require EVIOCREVOKE. */
+                r = -ENODEV;
+                goto err_dev;
+        }
+
+        /* search for an existing seat device and return it if available */
+        sd->device = hashmap_get(sd->session->manager->devices, sp);
+        if (!sd->device) {
+                /* The caller might have gotten the udev event before we were
+                 * able to process it. Hence, fake the "add" event and let the
+                 * logind-manager handle the new device. */
+                r = manager_process_seat_device(sd->session->manager, dev);
+                if (r < 0)
+                        goto err_dev;
+
+                /* if it's still not available, then the device is invalid */
+                sd->device = hashmap_get(sd->session->manager->devices, sp);
+                if (!sd->device) {
+                        r = -ENODEV;
+                        goto err_dev;
+                }
+        }
+
+        if (sd->device->seat != sd->session->seat) {
+                r = -EPERM;
+                goto err_dev;
+        }
+
+        sd->node = strdup(node);
+        if (!sd->node) {
+                r = -ENOMEM;
+                goto err_dev;
+        }
+
+        r = 0;
+err_dev:
+        udev_device_unref(p ? : dev);
+        return r;
+}
+
+int session_device_new(Session *s, dev_t dev, SessionDevice **out) {
+        SessionDevice *sd;
+        int r;
+
+        assert(s);
+        assert(out);
+
+        if (!s->seat)
+                return -EPERM;
+
+        sd = new0(SessionDevice, 1);
+        if (!sd)
+                return -ENOMEM;
+
+        sd->session = s;
+        sd->dev = dev;
+        sd->fd = -1;
+        sd->type = DEVICE_TYPE_UNKNOWN;
+
+        r = session_device_verify(sd);
+        if (r < 0)
+                goto error;
+
+        assert_cc(sizeof(unsigned long) >= sizeof(dev_t));
+
+        r = hashmap_put(s->devices, ULONG_TO_PTR((unsigned long)sd->dev), sd);
+        if (r < 0) {
+                r = -ENOMEM;
+                goto error;
+        }
+
+        /* Open the device for the first time. We need a valid fd to pass back
+         * to the caller. If the session is not active, this _might_ immediately
+         * revoke access and thus invalidate the fd. But this is still needed
+         * to pass a valid fd back. */
+        sd->active = session_is_active(s);
+        sd->fd = session_device_open(sd, sd->active);
+        if (sd->fd < 0)
+                goto error;
+
+        LIST_PREPEND(SessionDevice, sd_by_device, sd->device->session_devices, sd);
+
+        *out = sd;
+        return 0;
+
+error:
+        hashmap_remove(s->devices, ULONG_TO_PTR((unsigned long)sd->dev));
+        free(sd->node);
+        free(sd);
+        return r;
+}
+
+void session_device_free(SessionDevice *sd) {
+        assert(sd);
+
+        session_device_stop(sd);
+        session_device_notify(sd, SESSION_DEVICE_RELEASE);
+        close_nointr_nofail(sd->fd);
+
+        LIST_REMOVE(SessionDevice, sd_by_device, sd->device->session_devices, sd);
+
+        hashmap_remove(sd->session->devices, ULONG_TO_PTR((unsigned long)sd->dev));
+
+        free(sd->node);
+        free(sd);
+}
+
+void session_device_complete_pause(SessionDevice *sd) {
+        if (!sd->active)
+                return;
+
+        session_device_stop(sd);
+}
+
+void session_device_resume_all(Session *s) {
+        SessionDevice *sd;
+        Iterator i;
+        int r;
+
+        assert(s);
+
+        HASHMAP_FOREACH(sd, s->devices, i) {
+                if (!sd->active) {
+                        r = session_device_start(sd);
+                        if (!r)
+                                session_device_notify(sd, SESSION_DEVICE_RESUME);
+                }
+        }
+}
+
+void session_device_pause_all(Session *s) {
+        SessionDevice *sd;
+        Iterator i;
+
+        assert(s);
+
+        HASHMAP_FOREACH(sd, s->devices, i) {
+                if (sd->active) {
+                        session_device_stop(sd);
+                        session_device_notify(sd, SESSION_DEVICE_PAUSE);
+                }
+        }
+}