logind: don't rely on downgrade-to-bool

[thirdparty/systemd.git] / src / login / logind-session.c

/* SPDX-License-Identifier: LGPL-2.1+ */

#include <errno.h>
#include <fcntl.h>
#include <linux/kd.h>
#include <linux/vt.h>
#include <signal.h>
#include <stdio_ext.h>
#include <string.h>
#include <sys/ioctl.h>
#include <unistd.h>

#include "sd-messages.h"

#include "alloc-util.h"
#include "audit-util.h"
#include "bus-error.h"
#include "bus-util.h"
#include "escape.h"
#include "fd-util.h"
#include "fileio.h"
#include "format-util.h"
#include "io-util.h"
#include "logind-session.h"
#include "mkdir.h"
#include "parse-util.h"
#include "path-util.h"
#include "process-util.h"
#include "string-table.h"
#include "terminal-util.h"
#include "user-util.h"
#include "util.h"

#define RELEASE_USEC (20*USEC_PER_SEC)

static void session_remove_fifo(Session *s);

int session_new(Session **ret, Manager *m, const char *id) {
        _cleanup_(session_freep) Session *s = NULL;
        int r;

        assert(ret);
        assert(m);
        assert(id);

        if (!session_id_valid(id))
                return -EINVAL;

        s = new(Session, 1);
        if (!s)
                return -ENOMEM;

        *s = (Session) {
                .manager = m,
                .fifo_fd = -1,
                .vtfd = -1,
                .audit_id = AUDIT_SESSION_INVALID,
        };

        s->state_file = strappend("/run/systemd/sessions/", id);
        if (!s->state_file)
                return -ENOMEM;

        s->id = basename(s->state_file);

        s->devices = hashmap_new(&devt_hash_ops);
        if (!s->devices)
                return -ENOMEM;

        r = hashmap_put(m->sessions, s->id, s);
        if (r < 0)
                return r;

        *ret = TAKE_PTR(s);
        return 0;
}

Session* session_free(Session *s) {
        SessionDevice *sd;

        if (!s)
                return NULL;

        if (s->in_gc_queue)
                LIST_REMOVE(gc_queue, s->manager->session_gc_queue, s);

        s->timer_event_source = sd_event_source_unref(s->timer_event_source);

        session_remove_fifo(s);

        session_drop_controller(s);

        while ((sd = hashmap_first(s->devices)))
                session_device_free(sd);

        hashmap_free(s->devices);

        if (s->user) {
                LIST_REMOVE(sessions_by_user, s->user->sessions, s);

                if (s->user->display == s)
                        s->user->display = NULL;
        }

        if (s->seat) {
                if (s->seat->active == s)
                        s->seat->active = NULL;
                if (s->seat->pending_switch == s)
                        s->seat->pending_switch = NULL;

                seat_evict_position(s->seat, s);
                LIST_REMOVE(sessions_by_seat, s->seat->sessions, s);
        }

        if (s->scope) {
                hashmap_remove(s->manager->session_units, s->scope);
                free(s->scope);
        }

        free(s->scope_job);

        sd_bus_message_unref(s->create_message);

        free(s->tty);
        free(s->display);
        free(s->remote_host);
        free(s->remote_user);
        free(s->service);
        free(s->desktop);

        hashmap_remove(s->manager->sessions, s->id);

        free(s->state_file);

        return mfree(s);
}

void session_set_user(Session *s, User *u) {
        assert(s);
        assert(!s->user);

        s->user = u;
        LIST_PREPEND(sessions_by_user, u->sessions, s);
}

static void session_save_devices(Session *s, FILE *f) {
        SessionDevice *sd;
        Iterator i;

        if (!hashmap_isempty(s->devices)) {
                fprintf(f, "DEVICES=");
                HASHMAP_FOREACH(sd, s->devices, i)
                        fprintf(f, "%u:%u ", major(sd->dev), minor(sd->dev));
                fprintf(f, "\n");
        }
}

int session_save(Session *s) {
        _cleanup_free_ char *temp_path = NULL;
        _cleanup_fclose_ FILE *f = NULL;
        int r = 0;

        assert(s);

        if (!s->user)
                return -ESTALE;

        if (!s->started)
                return 0;

        r = mkdir_safe_label("/run/systemd/sessions", 0755, 0, 0, MKDIR_WARN_MODE);
        if (r < 0)
                goto fail;

        r = fopen_temporary(s->state_file, &f, &temp_path);
        if (r < 0)
                goto fail;

        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
        (void) fchmod(fileno(f), 0644);

        fprintf(f,
                "# This is private data. Do not parse.\n"
                "UID="UID_FMT"\n"
                "USER=%s\n"
                "ACTIVE=%i\n"
                "IS_DISPLAY=%i\n"
                "STATE=%s\n"
                "REMOTE=%i\n",
                s->user->uid,
                s->user->name,
                session_is_active(s),
                s->user->display == s,
                session_state_to_string(session_get_state(s)),
                s->remote);

        if (s->type >= 0)
                fprintf(f, "TYPE=%s\n", session_type_to_string(s->type));

        if (s->class >= 0)
                fprintf(f, "CLASS=%s\n", session_class_to_string(s->class));

        if (s->scope)
                fprintf(f, "SCOPE=%s\n", s->scope);
        if (s->scope_job)
                fprintf(f, "SCOPE_JOB=%s\n", s->scope_job);

        if (s->fifo_path)
                fprintf(f, "FIFO=%s\n", s->fifo_path);

        if (s->seat)
                fprintf(f, "SEAT=%s\n", s->seat->id);

        if (s->tty)
                fprintf(f, "TTY=%s\n", s->tty);

        if (s->display)
                fprintf(f, "DISPLAY=%s\n", s->display);

        if (s->remote_host) {
                _cleanup_free_ char *escaped;

                escaped = cescape(s->remote_host);
                if (!escaped) {
                        r = -ENOMEM;
                        goto fail;
                }

                fprintf(f, "REMOTE_HOST=%s\n", escaped);
        }

        if (s->remote_user) {
                _cleanup_free_ char *escaped;

                escaped = cescape(s->remote_user);
                if (!escaped) {
                        r = -ENOMEM;
                        goto fail;
                }

                fprintf(f, "REMOTE_USER=%s\n", escaped);
        }

        if (s->service) {
                _cleanup_free_ char *escaped;

                escaped = cescape(s->service);
                if (!escaped) {
                        r = -ENOMEM;
                        goto fail;
                }

                fprintf(f, "SERVICE=%s\n", escaped);
        }

        if (s->desktop) {
                _cleanup_free_ char *escaped;

                escaped = cescape(s->desktop);
                if (!escaped) {
                        r = -ENOMEM;
                        goto fail;
                }

                fprintf(f, "DESKTOP=%s\n", escaped);
        }

        if (s->seat && seat_has_vts(s->seat))
                fprintf(f, "VTNR=%u\n", s->vtnr);

        if (!s->vtnr)
                fprintf(f, "POSITION=%u\n", s->position);

        if (pid_is_valid(s->leader))
                fprintf(f, "LEADER="PID_FMT"\n", s->leader);

        if (audit_session_is_valid(s->audit_id))
                fprintf(f, "AUDIT=%"PRIu32"\n", s->audit_id);

        if (dual_timestamp_is_set(&s->timestamp))
                fprintf(f,
                        "REALTIME="USEC_FMT"\n"
                        "MONOTONIC="USEC_FMT"\n",
                        s->timestamp.realtime,
                        s->timestamp.monotonic);

        if (s->controller) {
                fprintf(f, "CONTROLLER=%s\n", s->controller);
                session_save_devices(s, f);
        }

        r = fflush_and_check(f);
        if (r < 0)
                goto fail;

        if (rename(temp_path, s->state_file) < 0) {
                r = -errno;
                goto fail;
        }

        return 0;

fail:
        (void) unlink(s->state_file);

        if (temp_path)
                (void) unlink(temp_path);

        return log_error_errno(r, "Failed to save session data %s: %m", s->state_file);
}

static int session_load_devices(Session *s, const char *devices) {
        const char *p;
        int r = 0;

        assert(s);

        for (p = devices;;) {
                _cleanup_free_ char *word = NULL;
                SessionDevice *sd;
                dev_t dev;
                int k;

                k = extract_first_word(&p, &word, NULL, 0);
                if (k == 0)
                        break;
                if (k < 0) {
                        r = k;
                        break;
                }

                k = parse_dev(word, &dev);
                if (k < 0) {
                        r = k;
                        continue;
                }

                /* The file descriptors for loaded devices will be reattached later. */
                k = session_device_new(s, dev, false, &sd);
                if (k < 0)
                        r = k;
        }

        if (r < 0)
                log_error_errno(r, "Loading session devices for session %s failed: %m", s->id);

        return r;
}

int session_load(Session *s) {
        _cleanup_free_ char *remote = NULL,
                *seat = NULL,
                *vtnr = NULL,
                *state = NULL,
                *position = NULL,
                *leader = NULL,
                *type = NULL,
                *class = NULL,
                *uid = NULL,
                *realtime = NULL,
                *monotonic = NULL,
                *controller = NULL,
                *active = NULL,
                *devices = NULL,
                *is_display = NULL;

        int k, r;

        assert(s);

        r = parse_env_file(NULL, s->state_file, NEWLINE,
                           "REMOTE",         &remote,
                           "SCOPE",          &s->scope,
                           "SCOPE_JOB",      &s->scope_job,
                           "FIFO",           &s->fifo_path,
                           "SEAT",           &seat,
                           "TTY",            &s->tty,
                           "DISPLAY",        &s->display,
                           "REMOTE_HOST",    &s->remote_host,
                           "REMOTE_USER",    &s->remote_user,
                           "SERVICE",        &s->service,
                           "DESKTOP",        &s->desktop,
                           "VTNR",           &vtnr,
                           "STATE",          &state,
                           "POSITION",       &position,
                           "LEADER",         &leader,
                           "TYPE",           &type,
                           "CLASS",          &class,
                           "UID",            &uid,
                           "REALTIME",       &realtime,
                           "MONOTONIC",      &monotonic,
                           "CONTROLLER",     &controller,
                           "ACTIVE",         &active,
                           "DEVICES",        &devices,
                           "IS_DISPLAY",     &is_display,
                           NULL);

        if (r < 0)
                return log_error_errno(r, "Failed to read %s: %m", s->state_file);

        if (!s->user) {
                uid_t u;
                User *user;

                if (!uid) {
                        log_error("UID not specified for session %s", s->id);
                        return -ENOENT;
                }

                r = parse_uid(uid, &u);
                if (r < 0)  {
                        log_error("Failed to parse UID value %s for session %s.", uid, s->id);
                        return r;
                }

                user = hashmap_get(s->manager->users, UID_TO_PTR(u));
                if (!user) {
                        log_error("User of session %s not known.", s->id);
                        return -ENOENT;
                }

                session_set_user(s, user);
        }

        if (remote) {
                k = parse_boolean(remote);
                if (k >= 0)
                        s->remote = k;
        }

        if (vtnr)
                safe_atou(vtnr, &s->vtnr);

        if (seat && !s->seat) {
                Seat *o;

                o = hashmap_get(s->manager->seats, seat);
                if (o)
                        r = seat_attach_session(o, s);
                if (!o || r < 0)
                        log_error("Cannot attach session %s to seat %s", s->id, seat);
        }

        if (!s->seat || !seat_has_vts(s->seat))
                s->vtnr = 0;

        if (position && s->seat) {
                unsigned int npos;

                safe_atou(position, &npos);
                seat_claim_position(s->seat, s, npos);
        }

        if (leader) {
                if (parse_pid(leader, &s->leader) >= 0)
                        (void) audit_session_from_pid(s->leader, &s->audit_id);
        }

        if (type) {
                SessionType t;

                t = session_type_from_string(type);
                if (t >= 0)
                        s->type = t;
        }

        if (class) {
                SessionClass c;

                c = session_class_from_string(class);
                if (c >= 0)
                        s->class = c;
        }

        if (state && streq(state, "closing"))
                s->stopping = true;

        if (s->fifo_path) {
                int fd;

                /* If we open an unopened pipe for reading we will not
                   get an EOF. to trigger an EOF we hence open it for
                   writing, but close it right away which then will
                   trigger the EOF. This will happen immediately if no
                   other process has the FIFO open for writing, i. e.
                   when the session died before logind (re)started. */

                fd = session_create_fifo(s);
                safe_close(fd);
        }

        if (realtime)
                timestamp_deserialize(realtime, &s->timestamp.realtime);
        if (monotonic)
                timestamp_deserialize(monotonic, &s->timestamp.monotonic);

        if (active) {
                k = parse_boolean(active);
                if (k >= 0)
                        s->was_active = k;
        }

        if (is_display) {
                /* Note that when enumerating users are loaded before sessions, hence the display session to use is
                 * something we have to store along with the session and not the user, as in that case we couldn't
                 * apply it at the time we load the user. */

                k = parse_boolean(is_display);
                if (k < 0)
                        log_warning_errno(k, "Failed to parse IS_DISPLAY session property: %m");
                else if (k > 0)
                        s->user->display = s;
        }

        if (controller) {
                if (bus_name_has_owner(s->manager->bus, controller, NULL) > 0) {
                        session_set_controller(s, controller, false, false);
                        session_load_devices(s, devices);
                } else
                        session_restore_vt(s);
        }

        return r;
}

int session_activate(Session *s) {
        unsigned int num_pending;

        assert(s);
        assert(s->user);

        if (!s->seat)
                return -EOPNOTSUPP;

        if (s->seat->active == s)
                return 0;

        /* on seats with VTs, we let VTs manage session-switching */
        if (seat_has_vts(s->seat)) {
                if (s->vtnr == 0)
                        return -EOPNOTSUPP;

                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_start_scope(Session *s, sd_bus_message *properties) {
        int r;

        assert(s);
        assert(s->user);

        if (!s->scope) {
                _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
                _cleanup_free_ char *scope = NULL;
                char *job = NULL;
                const char *description;

                scope = strjoin("session-", s->id, ".scope");
                if (!scope)
                        return log_oom();

                description = strjoina("Session ", s->id, " of user ", s->user->name);

                r = manager_start_scope(
                                s->manager,
                                scope,
                                s->leader,
                                s->user->slice,
                                description,
                                "systemd-logind.service",
                                "systemd-user-sessions.service",
                                properties,
                                &error,
                                &job);
                if (r < 0)
                        return log_error_errno(r, "Failed to start session scope %s: %s", scope, bus_error_message(&error, r));


                s->scope = TAKE_PTR(scope);
                free_and_replace(s->scope_job, job);
        }

        if (s->scope)
                (void) hashmap_put(s->manager->session_units, s->scope, s);

        return 0;
}

int session_start(Session *s, sd_bus_message *properties) {
        int r;

        assert(s);

        if (!s->user)
                return -ESTALE;

        if (s->started)
                return 0;

        r = user_start(s->user);
        if (r < 0)
                return r;

        /* Create cgroup */
        r = session_start_scope(s, properties);
        if (r < 0)
                return r;

        log_struct(s->class == SESSION_BACKGROUND ? LOG_DEBUG : LOG_INFO,
                   "MESSAGE_ID=" SD_MESSAGE_SESSION_START_STR,
                   "SESSION_ID=%s", s->id,
                   "USER_ID=%s", s->user->name,
                   "LEADER="PID_FMT, s->leader,
                   LOG_MESSAGE("New session %s of user %s.", s->id, s->user->name));

        if (!dual_timestamp_is_set(&s->timestamp))
                dual_timestamp_get(&s->timestamp);

        if (s->seat)
                seat_read_active_vt(s->seat);

        s->started = true;

        user_elect_display(s->user);

        /* Save data */
        session_save(s);
        user_save(s->user);
        if (s->seat)
                seat_save(s->seat);

        /* Send signals */
        session_send_signal(s, true);
        user_send_changed(s->user, "Display", NULL);
        if (s->seat) {
                if (s->seat->active == s)
                        seat_send_changed(s->seat, "ActiveSession", NULL);
        }

        return 0;
}

static int session_stop_scope(Session *s, bool force) {
        _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
        int r;

        assert(s);

        if (!s->scope)
                return 0;

        /* Let's always abandon the scope first. This tells systemd that we are not interested anymore, and everything
         * that is left in the scope is "left-over". Informing systemd about this has the benefit that it will log
         * when killing any processes left after this point. */
        r = manager_abandon_scope(s->manager, s->scope, &error);
        if (r < 0)
                log_warning_errno(r, "Failed to abandon session scope, ignoring: %s", bus_error_message(&error, r));

        /* Optionally, let's kill everything that's left now. */
        if (force || manager_shall_kill(s->manager, s->user->name)) {
                char *job = NULL;

                r = manager_stop_unit(s->manager, s->scope, &error, &job);
                if (r < 0)
                        return log_error_errno(r, "Failed to stop session scope: %s", bus_error_message(&error, r));

                free(s->scope_job);
                s->scope_job = job;
        } else {
                s->scope_job = mfree(s->scope_job);

                /* With no killing, this session is allowed to persist in "closing" state indefinitely.
                 * Therefore session stop and session removal may be two distinct events.
                 * Session stop is quite significant on its own, let's log it. */
                log_struct(s->class == SESSION_BACKGROUND ? LOG_DEBUG : LOG_INFO,
                           "SESSION_ID=%s", s->id,
                           "USER_ID=%s", s->user->name,
                           "LEADER="PID_FMT, s->leader,
                           LOG_MESSAGE("Session %s logged out. Waiting for processes to exit.", s->id));
        }

        return 0;
}

int session_stop(Session *s, bool force) {
        int r;

        assert(s);

        if (!s->user)
                return -ESTALE;

        s->timer_event_source = sd_event_source_unref(s->timer_event_source);

        if (s->seat)
                seat_evict_position(s->seat, s);

        /* We are going down, don't care about FIFOs anymore */
        session_remove_fifo(s);

        /* Kill cgroup */
        r = session_stop_scope(s, force);

        s->stopping = true;

        user_elect_display(s->user);

        session_save(s);
        user_save(s->user);

        return r;
}

int session_finalize(Session *s) {
        SessionDevice *sd;

        assert(s);

        if (!s->user)
                return -ESTALE;

        if (s->started)
                log_struct(s->class == SESSION_BACKGROUND ? LOG_DEBUG : LOG_INFO,
                           "MESSAGE_ID=" SD_MESSAGE_SESSION_STOP_STR,
                           "SESSION_ID=%s", s->id,
                           "USER_ID=%s", s->user->name,
                           "LEADER="PID_FMT, s->leader,
                           LOG_MESSAGE("Removed session %s.", s->id));

        s->timer_event_source = sd_event_source_unref(s->timer_event_source);

        if (s->seat)
                seat_evict_position(s->seat, s);

        /* Kill session devices */
        while ((sd = hashmap_first(s->devices)))
                session_device_free(sd);

        (void) unlink(s->state_file);
        session_add_to_gc_queue(s);
        user_add_to_gc_queue(s->user);

        if (s->started) {
                session_send_signal(s, false);
                s->started = false;
        }

        if (s->seat) {
                if (s->seat->active == s)
                        seat_set_active(s->seat, NULL);

                seat_save(s->seat);
        }

        user_save(s->user);
        user_send_changed(s->user, "Display", NULL);

        return 0;
}

static int release_timeout_callback(sd_event_source *es, uint64_t usec, void *userdata) {
        Session *s = userdata;

        assert(es);
        assert(s);

        session_stop(s, false);
        return 0;
}

int session_release(Session *s) {
        assert(s);

        if (!s->started || s->stopping)
                return 0;

        if (s->timer_event_source)
                return 0;

        return sd_event_add_time(s->manager->event,
                                 &s->timer_event_source,
                                 CLOCK_MONOTONIC,
                                 now(CLOCK_MONOTONIC) + RELEASE_USEC, 0,
                                 release_timeout_callback, s);
}

bool session_is_active(Session *s) {
        assert(s);

        if (!s->seat)
                return true;

        return s->seat->active == s;
}

static int get_tty_atime(const char *tty, usec_t *atime) {
        _cleanup_free_ char *p = NULL;
        struct stat st;

        assert(tty);
        assert(atime);

        if (!path_is_absolute(tty)) {
                p = strappend("/dev/", tty);
                if (!p)
                        return -ENOMEM;

                tty = p;
        } else if (!path_startswith(tty, "/dev/"))
                return -ENOENT;

        if (lstat(tty, &st) < 0)
                return -errno;

        *atime = timespec_load(&st.st_atim);
        return 0;
}

static int get_process_ctty_atime(pid_t pid, usec_t *atime) {
        _cleanup_free_ char *p = NULL;
        int r;

        assert(pid > 0);
        assert(atime);

        r = get_ctty(pid, NULL, &p);
        if (r < 0)
                return r;

        return get_tty_atime(p, atime);
}

int session_get_idle_hint(Session *s, dual_timestamp *t) {
        usec_t atime = 0, n;
        int r;

        assert(s);

        /* Explicit idle hint is set */
        if (s->idle_hint) {
                if (t)
                        *t = s->idle_hint_timestamp;

                return s->idle_hint;
        }

        /* Graphical sessions should really implement a real
         * idle hint logic */
        if (SESSION_TYPE_IS_GRAPHICAL(s->type))
                goto dont_know;

        /* For sessions with an explicitly configured tty, let's check
         * its atime */
        if (s->tty) {
                r = get_tty_atime(s->tty, &atime);
                if (r >= 0)
                        goto found_atime;
        }

        /* For sessions with a leader but no explicitly configured
         * tty, let's check the controlling tty of the leader */
        if (s->leader > 0) {
                r = get_process_ctty_atime(s->leader, &atime);
                if (r >= 0)
                        goto found_atime;
        }

dont_know:
        if (t)
                *t = s->idle_hint_timestamp;

        return 0;

found_atime:
        if (t)
                dual_timestamp_from_realtime(t, atime);

        n = now(CLOCK_REALTIME);

        if (s->manager->idle_action_usec <= 0)
                return 0;

        return atime + s->manager->idle_action_usec <= n;
}

void session_set_idle_hint(Session *s, bool b) {
        assert(s);

        if (s->idle_hint == b)
                return;

        s->idle_hint = b;
        dual_timestamp_get(&s->idle_hint_timestamp);

        session_send_changed(s, "IdleHint", "IdleSinceHint", "IdleSinceHintMonotonic", NULL);

        if (s->seat)
                seat_send_changed(s->seat, "IdleHint", "IdleSinceHint", "IdleSinceHintMonotonic", NULL);

        user_send_changed(s->user, "IdleHint", "IdleSinceHint", "IdleSinceHintMonotonic", NULL);
        manager_send_changed(s->manager, "IdleHint", "IdleSinceHint", "IdleSinceHintMonotonic", NULL);
}

int session_get_locked_hint(Session *s) {
        assert(s);

        return s->locked_hint;
}

void session_set_locked_hint(Session *s, bool b) {
        assert(s);

        if (s->locked_hint == b)
                return;

        s->locked_hint = b;

        session_send_changed(s, "LockedHint", NULL);
}

static int session_dispatch_fifo(sd_event_source *es, int fd, uint32_t revents, void *userdata) {
        Session *s = userdata;

        assert(s);
        assert(s->fifo_fd == fd);

        /* EOF on the FIFO means the session died abnormally. */

        session_remove_fifo(s);
        session_stop(s, false);

        return 1;
}

int session_create_fifo(Session *s) {
        int r;

        assert(s);

        /* Create FIFO */
        if (!s->fifo_path) {
                r = mkdir_safe_label("/run/systemd/sessions", 0755, 0, 0, MKDIR_WARN_MODE);
                if (r < 0)
                        return r;

                if (asprintf(&s->fifo_path, "/run/systemd/sessions/%s.ref", s->id) < 0)
                        return -ENOMEM;

                if (mkfifo(s->fifo_path, 0600) < 0 && errno != EEXIST)
                        return -errno;
        }

        /* Open reading side */
        if (s->fifo_fd < 0) {
                s->fifo_fd = open(s->fifo_path, O_RDONLY|O_CLOEXEC|O_NONBLOCK);
                if (s->fifo_fd < 0)
                        return -errno;

        }

        if (!s->fifo_event_source) {
                r = sd_event_add_io(s->manager->event, &s->fifo_event_source, s->fifo_fd, 0, session_dispatch_fifo, s);
                if (r < 0)
                        return r;

                /* Let's make sure we noticed dead sessions before we process new bus requests (which might create new
                 * sessions). */
                r = sd_event_source_set_priority(s->fifo_event_source, SD_EVENT_PRIORITY_NORMAL-10);
                if (r < 0)
                        return r;
        }

        /* Open writing side */
        r = open(s->fifo_path, O_WRONLY|O_CLOEXEC|O_NONBLOCK);
        if (r < 0)
                return -errno;

        return r;
}

static void session_remove_fifo(Session *s) {
        assert(s);

        s->fifo_event_source = sd_event_source_unref(s->fifo_event_source);
        s->fifo_fd = safe_close(s->fifo_fd);

        if (s->fifo_path) {
                (void) unlink(s->fifo_path);
                s->fifo_path = mfree(s->fifo_path);
        }
}

bool session_may_gc(Session *s, bool drop_not_started) {
        int r;

        assert(s);

        if (drop_not_started && !s->started)
                return true;

        if (!s->user)
                return true;

        if (s->fifo_fd >= 0) {
                if (pipe_eof(s->fifo_fd) <= 0)
                        return false;
        }

        if (s->scope_job) {
                _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;

                r = manager_job_is_active(s->manager, s->scope_job, &error);
                if (r < 0)
                        log_debug_errno(r, "Failed to determine whether job '%s' is pending, ignoring: %s", s->scope_job, bus_error_message(&error, r));
                if (r != 0)
                        return false;
        }

        if (s->scope) {
                _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;

                r = manager_unit_is_active(s->manager, s->scope, &error);
                if (r < 0)
                        log_debug_errno(r, "Failed to determine whether unit '%s' is active, ignoring: %s", s->scope, bus_error_message(&error, r));
                if (r != 0)
                        return false;
        }

        return true;
}

void session_add_to_gc_queue(Session *s) {
        assert(s);

        if (s->in_gc_queue)
                return;

        LIST_PREPEND(gc_queue, s->manager->session_gc_queue, s);
        s->in_gc_queue = true;
}

SessionState session_get_state(Session *s) {
        assert(s);

        /* always check closing first */
        if (s->stopping || s->timer_event_source)
                return SESSION_CLOSING;

        if (s->scope_job || s->fifo_fd < 0)
                return SESSION_OPENING;

        if (session_is_active(s))
                return SESSION_ACTIVE;

        return SESSION_ONLINE;
}

int session_kill(Session *s, KillWho who, int signo) {
        assert(s);

        if (!s->scope)
                return -ESRCH;

        return manager_kill_unit(s->manager, s->scope, who, signo, NULL);
}

static int session_open_vt(Session *s) {
        char path[sizeof("/dev/tty") + DECIMAL_STR_MAX(s->vtnr)];

        if (s->vtnr < 1)
                return -ENODEV;

        if (s->vtfd >= 0)
                return s->vtfd;

        sprintf(path, "/dev/tty%u", s->vtnr);
        s->vtfd = open_terminal(path, O_RDWR | O_CLOEXEC | O_NONBLOCK | O_NOCTTY);
        if (s->vtfd < 0)
                return log_error_errno(s->vtfd, "cannot open VT %s of session %s: %m", path, s->id);

        return s->vtfd;
}

int session_prepare_vt(Session *s) {
        int vt, r;
        struct vt_mode mode = { 0 };

        if (s->vtnr < 1)
                return 0;

        vt = session_open_vt(s);
        if (vt < 0)
                return vt;

        r = fchown(vt, s->user->uid, -1);
        if (r < 0) {
                r = log_error_errno(errno,
                                    "Cannot change owner of /dev/tty%u: %m",
                                    s->vtnr);
                goto error;
        }

        r = ioctl(vt, KDSKBMODE, K_OFF);
        if (r < 0) {
                r = log_error_errno(errno,
                                    "Cannot set K_OFF on /dev/tty%u: %m",
                                    s->vtnr);
                goto error;
        }

        r = ioctl(vt, KDSETMODE, KD_GRAPHICS);
        if (r < 0) {
                r = log_error_errno(errno,
                                    "Cannot set KD_GRAPHICS on /dev/tty%u: %m",
                                    s->vtnr);
                goto error;
        }

        /* Oh, thanks to the VT layer, VT_AUTO does not work with KD_GRAPHICS.
         * So we need a dummy handler here which just acknowledges *all* VT
         * switch requests. */
        mode.mode = VT_PROCESS;
        mode.relsig = SIGRTMIN;
        mode.acqsig = SIGRTMIN + 1;
        r = ioctl(vt, VT_SETMODE, &mode);
        if (r < 0) {
                r = log_error_errno(errno,
                                    "Cannot set VT_PROCESS on /dev/tty%u: %m",
                                    s->vtnr);
                goto error;
        }

        return 0;

error:
        session_restore_vt(s);
        return r;
}

void session_restore_vt(Session *s) {

        static const struct vt_mode mode = {
                .mode = VT_AUTO,
        };

        int vt, old_fd;

        /* We need to get a fresh handle to the virtual terminal,
         * since the old file-descriptor is potentially in a hung-up
         * state after the controlling process exited; we do a
         * little dance to avoid having the terminal be available
         * for reuse before we've cleaned it up.
         */
        old_fd = TAKE_FD(s->vtfd);

        vt = session_open_vt(s);
        safe_close(old_fd);

        if (vt < 0)
                return;

        (void) ioctl(vt, KDSETMODE, KD_TEXT);

        (void) vt_reset_keyboard(vt);

        (void) ioctl(vt, VT_SETMODE, &mode);
        (void) fchown(vt, 0, (gid_t) -1);

        s->vtfd = safe_close(s->vtfd);
}

void session_leave_vt(Session *s) {
        int r;

        assert(s);

        /* This is called whenever we get a VT-switch signal from the kernel.
         * We acknowledge all of them unconditionally. Note that session are
         * free to overwrite those handlers and we only register them for
         * sessions with controllers. Legacy sessions are not affected.
         * However, if we switch from a non-legacy to a legacy session, we must
         * make sure to pause all device before acknowledging the switch. We
         * process the real switch only after we are notified via sysfs, so the
         * legacy session might have already started using the devices. If we
         * don't pause the devices before the switch, we might confuse the
         * session we switch to. */

        if (s->vtfd < 0)
                return;

        session_device_pause_all(s);
        r = ioctl(s->vtfd, VT_RELDISP, 1);
        if (r < 0)
                log_debug_errno(errno, "Cannot release VT of session %s: %m", s->id);
}

bool session_is_controller(Session *s, const char *sender) {
        assert(s);

        return streq_ptr(s->controller, sender);
}

static void session_release_controller(Session *s, bool notify) {
        _cleanup_free_ char *name = NULL;
        SessionDevice *sd;

        if (!s->controller)
                return;

        name = s->controller;

        /* By resetting the controller before releasing the devices, we won't
         * send notification signals. This avoids sending useless notifications
         * if the controller is released on disconnects. */
        if (!notify)
                s->controller = NULL;

        while ((sd = hashmap_first(s->devices)))
                session_device_free(sd);

        s->controller = NULL;
        s->track = sd_bus_track_unref(s->track);
}

static int on_bus_track(sd_bus_track *track, void *userdata) {
        Session *s = userdata;

        assert(track);
        assert(s);

        session_drop_controller(s);

        return 0;
}

int session_set_controller(Session *s, const char *sender, bool force, bool prepare) {
        _cleanup_free_ char *name = NULL;
        int r;

        assert(s);
        assert(sender);

        if (session_is_controller(s, sender))
                return 0;
        if (s->controller && !force)
                return -EBUSY;

        name = strdup(sender);
        if (!name)
                return -ENOMEM;

        s->track = sd_bus_track_unref(s->track);
        r = sd_bus_track_new(s->manager->bus, &s->track, on_bus_track, s);
        if (r < 0)
                return r;

        r = sd_bus_track_add_name(s->track, name);
        if (r < 0)
                return r;

        /* When setting a session controller, we forcibly mute the VT and set
         * it into graphics-mode. Applications can override that by changing
         * VT state after calling TakeControl(). However, this serves as a good
         * default and well-behaving controllers can now ignore VTs entirely.
         * Note that we reset the VT on ReleaseControl() and if the controller
         * exits.
         * If logind crashes/restarts, we restore the controller during restart
         * (without preparing the VT since the controller has probably overridden
         * VT state by now) or reset the VT in case it crashed/exited, too. */
        if (prepare) {
                r = session_prepare_vt(s);
                if (r < 0) {
                        s->track = sd_bus_track_unref(s->track);
                        return r;
                }
        }

        session_release_controller(s, true);
        s->controller = TAKE_PTR(name);
        session_save(s);

        return 0;
}

void session_drop_controller(Session *s) {
        assert(s);

        if (!s->controller)
                return;

        s->track = sd_bus_track_unref(s->track);
        session_release_controller(s, false);
        session_save(s);
        session_restore_vt(s);
}

static const char* const session_state_table[_SESSION_STATE_MAX] = {
        [SESSION_OPENING] = "opening",
        [SESSION_ONLINE] = "online",
        [SESSION_ACTIVE] = "active",
        [SESSION_CLOSING] = "closing"
};

DEFINE_STRING_TABLE_LOOKUP(session_state, SessionState);

static const char* const session_type_table[_SESSION_TYPE_MAX] = {
        [SESSION_UNSPECIFIED] = "unspecified",
        [SESSION_TTY] = "tty",
        [SESSION_X11] = "x11",
        [SESSION_WAYLAND] = "wayland",
        [SESSION_MIR] = "mir",
        [SESSION_WEB] = "web",
};

DEFINE_STRING_TABLE_LOOKUP(session_type, SessionType);

static const char* const session_class_table[_SESSION_CLASS_MAX] = {
        [SESSION_USER] = "user",
        [SESSION_GREETER] = "greeter",
        [SESSION_LOCK_SCREEN] = "lock-screen",
        [SESSION_BACKGROUND] = "background"
};

DEFINE_STRING_TABLE_LOOKUP(session_class, SessionClass);

static const char* const kill_who_table[_KILL_WHO_MAX] = {
        [KILL_LEADER] = "leader",
        [KILL_ALL] = "all"
};

DEFINE_STRING_TABLE_LOOKUP(kill_who, KillWho);