sd-login: beef up login api, to add monitoring and enumerating

8 files changed, 679 insertions, 37 deletions

diff --git a/src/install.c b/src/install.c
index e1c69444f9..9f415edc2e 100644
--- a/src/install.c
+++ b/src/install.c
@@ -1462,7 +1462,7 @@ int unit_file_disable(
 
         q = remove_marked_symlinks(remove_symlinks_to, config_path, changes, n_changes);
         if (r == 0)
-                r = 1;
+                r = q;
 
 finish:
         install_context_done(&c);
diff --git a/src/libsystemd-login.sym b/src/libsystemd-login.sym
index 708ef6ff25..cd5f52c341 100644
--- a/src/libsystemd-login.sym
+++ b/src/libsystemd-login.sym
@@ -11,13 +11,23 @@
 
 LIBSYSTEMD_LOGIN_31 {
 global:
+        sd_get_seats;
+        sd_get_sessions;
+        sd_get_uids;
+        sd_login_monitor_flush;
+        sd_login_monitor_get_fd;
+        sd_login_monitor_new;
+        sd_login_monitor_unref;
+        sd_pid_get_owner_uid;
         sd_pid_get_session;
         sd_seat_get_active;
+        sd_seat_get_sessions;
         sd_session_get_seat;
         sd_session_get_uid;
         sd_session_is_active;
+        sd_uid_get_seats;
+        sd_uid_get_sessions;
         sd_uid_get_state;
-        sd_uid_is_active_on_seat;
         sd_uid_is_on_seat;
 local:
         *;
diff --git a/src/logind-user.c b/src/logind-user.c
index 3a677ff707..3c245c0927 100644
--- a/src/logind-user.c
+++ b/src/logind-user.c
@@ -134,6 +134,44 @@ int user_save(User *u) {
                         "DISPLAY=%s\n",
                         u->display->id);
 
+        if (u->sessions) {
+                Session *i;
+
+                fputs("SESSIONS=", f);
+                LIST_FOREACH(sessions_by_user, i, u->sessions) {
+                        fprintf(f,
+                                "%s%c",
+                                i->id,
+                                i->sessions_by_seat_next ? ' ' : '\n');
+                }
+
+                fputs("SEATS=", f);
+                LIST_FOREACH(sessions_by_user, i, u->sessions) {
+                        if (i->seat)
+                                fprintf(f,
+                                        "%s%c",
+                                        i->seat->id,
+                                        i->sessions_by_seat_next ? ' ' : '\n');
+                }
+
+                fputs("ACTIVE_SESSIONS=", f);
+                LIST_FOREACH(sessions_by_user, i, u->sessions)
+                        if (session_is_active(i))
+                                fprintf(f,
+                                        "%lu%c",
+                                        (unsigned long) i->user->uid,
+                                        i->sessions_by_seat_next ? ' ' : '\n');
+
+                fputs("ACTIVE_SEATS=", f);
+                LIST_FOREACH(sessions_by_user, i, u->sessions) {
+                        if (session_is_active(i) && i->seat)
+                                fprintf(f,
+                                        "%s%c",
+                                        i->seat->id,
+                                        i->sessions_by_seat_next ? ' ' : '\n');
+                }
+        }
+
         fflush(f);
 
         if (ferror(f) || rename(temp_path, u->state_file) < 0) {
diff --git a/src/sd-login.c b/src/sd-login.c
index 3ae850d801..6dfc2d086e 100644
--- a/src/sd-login.c
+++ b/src/sd-login.c
@@ -22,15 +22,17 @@
 #include <unistd.h>
 #include <string.h>
 #include <errno.h>
+#include <sys/inotify.h>
 
 #include "util.h"
 #include "cgroup-util.h"
 #include "macro.h"
 #include "sd-login.h"
+#include "strv.h"
 
-_public_ int sd_pid_get_session(pid_t pid, char **session) {
-        int r;
+static int pid_get_cgroup(pid_t pid, char **root, char **cgroup) {
         char *cg_process, *cg_init, *p;
+        int r;
 
         if (pid == 0)
                 pid = getpid();
@@ -38,9 +40,6 @@ _public_ int sd_pid_get_session(pid_t pid, char **session) {
         if (pid <= 0)
                 return -EINVAL;
 
-        if (!session)
-                return -EINVAL;
-
         r = cg_get_by_pid(SYSTEMD_CGROUP_CONTROLLER, pid, &cg_process);
         if (r < 0)
                 return r;
@@ -63,26 +62,57 @@ _public_ int sd_pid_get_session(pid_t pid, char **session) {
 
         free(cg_init);
 
-        if (!startswith(p, "/user/")) {
-                free(cg_process);
-                return -ENOENT;
+        if (cgroup) {
+                char* c;
+
+                c = strdup(p);
+                if (!c) {
+                        free(cg_process);
+                        return -ENOMEM;
+                }
+
+                *cgroup = c;
         }
 
-        p += 6;
-        if (startswith(p, "shared/") || streq(p, "shared")) {
+        if (root) {
+                cg_process[p-cg_process] = 0;
+                *root = cg_process;
+        } else
                 free(cg_process);
+
+        return 0;
+}
+
+_public_ int sd_pid_get_session(pid_t pid, char **session) {
+        int r;
+        char *cgroup, *p;
+
+        if (!session)
+                return -EINVAL;
+
+        r = pid_get_cgroup(pid, NULL, &cgroup);
+        if (r < 0)
+                return r;
+
+        if (!startswith(cgroup, "/user/")) {
+                free(cgroup);
                 return -ENOENT;
         }
 
-        p = strchr(p, '/');
+        p = strchr(cgroup + 6, '/');
         if (!p) {
-                free(cg_process);
+                free(cgroup);
                 return -ENOENT;
         }
 
         p++;
+        if (startswith(p, "shared/") || streq(p, "shared")) {
+                free(cgroup);
+                return -ENOENT;
+        }
+
         p = strndup(p, strcspn(p, "/"));
-        free(cg_process);
+        free(cgroup);
 
         if (!p)
                 return -ENOMEM;
@@ -91,6 +121,54 @@ _public_ int sd_pid_get_session(pid_t pid, char **session) {
         return 0;
 }
 
+_public_ int sd_pid_get_owner_uid(pid_t pid, uid_t *uid) {
+        int r;
+        char *root, *cgroup, *p, *cc;
+        struct stat st;
+
+        if (!uid)
+                return -EINVAL;
+
+        r = pid_get_cgroup(pid, &root, &cgroup);
+        if (r < 0)
+                return r;
+
+        if (!startswith(cgroup, "/user/")) {
+                free(cgroup);
+                free(root);
+                return -ENOENT;
+        }
+
+        p = strchr(cgroup + 6, '/');
+        if (!p) {
+                free(cgroup);
+                return -ENOENT;
+        }
+
+        p++;
+        p += strcspn(p, "/");
+        *p = 0;
+
+        r = cg_get_path(SYSTEMD_CGROUP_CONTROLLER, root, cgroup, &cc);
+        free(root);
+        free(cgroup);
+
+        if (r < 0)
+                return -ENOMEM;
+
+        r = lstat(cc, &st);
+        free(cc);
+
+        if (r < 0)
+                return -errno;
+
+        if (!S_ISDIR(st.st_mode))
+                return -ENOTDIR;
+
+        *uid = st.st_uid;
+        return 0;
+}
+
 _public_ int sd_uid_get_state(uid_t uid, char**state) {
         char *p, *s = NULL;
         int r;
@@ -122,19 +200,22 @@ _public_ int sd_uid_get_state(uid_t uid, char**state) {
         return 0;
 }
 
-static int uid_is_on_seat_internal(uid_t uid, const char *seat, const char *variable) {
+_public_ int sd_uid_is_on_seat(uid_t uid, int require_active, const char *seat) {
         char *p, *w, *t, *state, *s = NULL;
         size_t l;
         int r;
+        const char *variable;
 
         if (!seat)
                 return -EINVAL;
 
+        variable = require_active ? "ACTIVE_UID" : "UIDS";
+
         p = strappend("/run/systemd/seats/", seat);
         if (!p)
                 return -ENOMEM;
 
-        r = parse_env_file(p, NEWLINE, "UIDS", &s, NULL);
+        r = parse_env_file(p, NEWLINE, variable, &s, NULL);
         free(p);
 
         if (r < 0) {
@@ -165,12 +246,54 @@ static int uid_is_on_seat_internal(uid_t uid, const char *seat, const char *vari
         return 0;
 }
 
-_public_ int sd_uid_is_on_seat(uid_t uid, const char *seat) {
-        return uid_is_on_seat_internal(uid, seat, "UIDS");
+static int uid_get_array(uid_t uid, const char *variable, char ***array) {
+        char *p, *s = NULL;
+        char **a;
+        int r;
+
+        if (!array)
+                return -EINVAL;
+
+        if (asprintf(&p, "/run/systemd/users/%lu", (unsigned long) uid) < 0)
+                return -ENOMEM;
+
+        r = parse_env_file(p, NEWLINE,
+                           variable, &s,
+                           NULL);
+        free(p);
+
+        if (r < 0) {
+                free(s);
+
+                if (r == -ENOENT) {
+                        *array = NULL;
+                        return 0;
+                }
+
+                return r;
+        }
+
+        if (!s) {
+                *array = NULL;
+                return 0;
+        }
+
+        a = strv_split(s, " ");
+        free(s);
+
+        if (!a)
+                return -ENOMEM;
+
+        *array = a;
+        return 0;
+}
+
+_public_ int sd_uid_get_sessions(uid_t uid, int require_active, char ***sessions) {
+        return uid_get_array(uid, require_active ? "ACTIVE_SESSIONS" : "SESSIONS", sessions);
 }
 
-_public_ int sd_uid_is_active_on_seat(uid_t uid, const char *seat) {
-        return uid_is_on_seat_internal(uid, seat, "ACTIVE_UID");
+_public_ int sd_uid_get_seats(uid_t uid, int require_active, char ***seats) {
+        return uid_get_array(uid, require_active ? "ACTIVE_SEATS" : "SEATS", seats);
 }
 
 _public_ int sd_session_is_active(const char *session) {
@@ -291,25 +414,21 @@ _public_ int sd_seat_get_active(const char *seat, char **session, uid_t *uid) {
 
         if (session && !s)  {
                 free(t);
-                return -EIO;
+                return -ENOENT;
         }
 
         if (uid && !t) {
                 free(s);
-                return -EIO;
+                return -ENOENT;
         }
 
         if (uid && t) {
-                unsigned long ul;
-
-                r = safe_atolu(t, &ul);
+                r = parse_uid(t, uid);
                 if (r < 0) {
                         free(t);
                         free(s);
                         return r;
                 }
-
-                *uid = (uid_t) ul;
         }
 
         free(t);
@@ -321,3 +440,254 @@ _public_ int sd_seat_get_active(const char *seat, char **session, uid_t *uid) {
 
         return 0;
 }
+
+_public_ int sd_seat_get_sessions(const char *seat, char ***sessions, uid_t **uids, unsigned *n_uids) {
+        char *p, *s = NULL, *t = NULL, **a = NULL;
+        uid_t *b = NULL;
+        unsigned n = 0;
+        int r;
+
+        if (!seat)
+                return -EINVAL;
+
+        if (!sessions && !uids)
+                return -EINVAL;
+
+        p = strappend("/run/systemd/seats/", seat);
+        if (!p)
+                return -ENOMEM;
+
+        r = parse_env_file(p, NEWLINE,
+                           "SESSIONS", &s,
+                           "ACTIVE_SESSIONS", &t,
+                           NULL);
+        free(p);
+
+        if (r < 0) {
+                free(s);
+                free(t);
+                return r;
+        }
+
+        if (sessions && s) {
+                a = strv_split(s, " ");
+                if (!a) {
+                        free(s);
+                        free(t);
+                        return -ENOMEM;
+                }
+        }
+
+        free(s);
+
+        if (uids && t) {
+                char *w, *state;
+                size_t l;
+                unsigned i = 0;
+
+                FOREACH_WORD(w, l, t, state)
+                        n++;
+
+                b = new(uid_t, n);
+                if (!b) {
+                        strv_free(a);
+                        return -ENOMEM;
+                }
+
+                FOREACH_WORD(w, l, t, state) {
+                        char *k;
+
+                        k = strndup(w, l);
+                        if (!k) {
+                                free(t);
+                                free(b);
+                                return -ENOMEM;
+                        }
+
+                        r = parse_uid(k, b + i);
+                        free(k);
+                        if (r < 0)
+                                continue;
+
+                        i++;
+                }
+        }
+
+        free(t);
+
+        if (sessions)
+                *sessions = a;
+
+        if (uids)
+                *uids = b;
+
+        if (n_uids)
+                *n_uids = n;
+
+        return 0;
+}
+
+_public_ int sd_get_seats(char ***seats) {
+
+        if (!seats)
+                return -EINVAL;
+
+        return get_files_in_directory("/run/systemd/seats/", seats);
+}
+
+_public_ int sd_get_sessions(char ***sessions) {
+
+        if (!sessions)
+                return -EINVAL;
+
+        return get_files_in_directory("/run/systemd/sessions/", sessions);
+}
+
+_public_ int sd_get_uids(uid_t **users) {
+        DIR *d;
+        int r = 0;
+        unsigned n = 0;
+        uid_t *l = NULL;
+
+        if (!users)
+                return -EINVAL;
+
+        d = opendir("/run/systemd/users/");
+        for (;;) {
+                struct dirent buffer, *de;
+                int k;
+                uid_t uid;
+
+                k = readdir_r(d, &buffer, &de);
+                if (k != 0) {
+                        r = -k;
+                        goto finish;
+                }
+
+                if (!de)
+                        break;
+
+                dirent_ensure_type(d, de);
+
+                if (!dirent_is_file(de))
+                        continue;
+
+                k = parse_uid(de->d_name, &uid);
+                if (k < 0)
+                        continue;
+
+                if ((unsigned) r >= n) {
+                        uid_t *t;
+
+                        n = MAX(16, 2*r);
+                        t = realloc(l, sizeof(uid_t) * n);
+                        if (!t) {
+                                r = -ENOMEM;
+                                goto finish;
+                        }
+
+                        l = t;
+                }
+
+                assert((unsigned) r < n);
+                l[r++] = uid;
+        }
+
+finish:
+        if (d)
+                closedir(d);
+
+        if (r >= 0)
+                *users = l;
+        else
+                free(l);
+
+        return r;
+}
+
+static inline int MONITOR_TO_FD(sd_login_monitor *m) {
+        return (int) (unsigned long) m - 1;
+}
+
+static inline sd_login_monitor* FD_TO_MONITOR(int fd) {
+        return (sd_login_monitor*) (unsigned long) (fd + 1);
+}
+
+_public_ int sd_login_monitor_new(const char *category, sd_login_monitor **m) {
+        const char *path;
+        int fd, k;
+        bool good = false;
+
+        if (!m)
+                return -EINVAL;
+
+        fd = inotify_init1(IN_NONBLOCK|IN_CLOEXEC);
+        if (fd < 0)
+                return errno;
+
+        if (!category || streq(category, "seat")) {
+                k = inotify_add_watch(fd, "/run/systemd/seats/", IN_MOVED_TO|IN_DELETE);
+                if (k < 0) {
+                        close_nointr_nofail(fd);
+                        return -errno;
+                }
+
+                good = true;
+        }
+
+        if (!category || streq(category, "session")) {
+                k = inotify_add_watch(fd, "/run/systemd/sessions/", IN_MOVED_TO|IN_DELETE);
+                if (k < 0) {
+                        close_nointr_nofail(fd);
+                        return -errno;
+                }
+
+                good = true;
+        }
+
+        if (!category || streq(category, "uid")) {
+                k = inotify_add_watch(fd, "/run/systemd/users/", IN_MOVED_TO|IN_DELETE);
+                if (k < 0) {
+                        close_nointr_nofail(fd);
+                        return -errno;
+                }
+
+                good = true;
+        }
+
+        if (!good) {
+                close_nointr(fd);
+                return -EINVAL;
+        }
+
+        *m = FD_TO_MONITOR(fd);
+        return 0;
+}
+
+_public_ sd_login_monitor* sd_login_monitor_unref(sd_login_monitor *m) {
+        int fd;
+
+        if (!m)
+                return NULL;
+
+        fd = MONITOR_TO_FD(m);
+        close_nointr(fd);
+
+        return NULL;
+}
+
+_public_ int sd_login_monitor_flush(sd_login_monitor *m) {
+
+        if (!m)
+                return -EINVAL;
+
+        return flush_fd(MONITOR_TO_FD(m));
+}
+
+_public_ int sd_login_monitor_get_fd(sd_login_monitor *m) {
+
+        if (!m)
+                return -EINVAL;
+
+        return MONITOR_TO_FD(m);
+}
diff --git a/src/sd-login.h b/src/sd-login.h
index f23ac80526..c6835e1235 100644
--- a/src/sd-login.h
+++ b/src/sd-login.h
@@ -24,17 +24,48 @@
 
 #include <sys/types.h>
 
-/* Get session from PID */
+/*
+ * A few points:
+ *
+ * Instead of returning an empty string array or empty uid array, we
+ * may return NULL.
+ *
+ * Free the data we return with libc free().
+ *
+ * We return error codes as negative errno, kernel-style.
+ *
+ * These functions access data in /proc, /sys/fs/cgroup and /run. All
+ * of these are virtual file systems, hence the accesses are
+ * relatively cheap.
+ */
+
+/* Get session from PID. Note that 'shared' processes of a user are
+ * not attached to a session, but only attached to a user. This will
+ * return an error for system processes and 'shared' processes of a
+ * user. */
 int sd_pid_get_session(pid_t pid, char **session);
 
+/* Get UID of the owner of the session of the PID (or in case the
+ * process is a 'shared' user process the UID of that user is
+ * returned). This will not return the UID of the process, but rather
+ * the UID of the owner of the cgroup the process is in. This will
+ * return an error for system processes. */
+int sd_pid_get_owner_uid(pid_t pid, uid_t *uid);
+
 /* Get state from uid. Possible states: offline, lingering, online, active */
 int sd_uid_get_state(uid_t uid, char**state);
 
-/* Return 1 if uid has session on seat */
-int sd_uid_is_on_seat(uid_t uid, const char *seat);
+/* Return 1 if uid has session on seat. If require_active is true will
+ * look for active sessions only. */
+int sd_uid_is_on_seat(uid_t uid, int require_active, const char *seat);
+
+/* Return sessions of user. If require_active is true will look
+ * for active sessions only. */
+int sd_uid_get_sessions(uid_t uid, int require_active, char ***sessions);
 
-/* Return 1 if uid has active session on seat */
-int sd_uid_is_active_on_seat(uid_t uid, const char *seat);
+/* Return seats of user is on. If require_active is true will look for
+ * active seats only.  */
+int sd_uid_get_seats(uid_t uid, int require_active, char ***seats);
 
 /* Return 1 if the session is a active */
 int sd_session_is_active(const char *session);
@@ -48,4 +79,32 @@ int sd_session_get_seat(const char *session, char **seat);
 /* Return active session and user of seat */
 int sd_seat_get_active(const char *seat, char **session, uid_t *uid);
 
+/* Return sessions and users on seat */
+int sd_seat_get_sessions(const char *seat, char ***sessions, uid_t **uid, unsigned *n_uids);
+
+/* Get all seats */
+int sd_get_seats(char ***seats);
+
+/* Get all sessions */
+int sd_get_sessions(char ***sessions);
+
+/* Get all logged in users */
+int sd_get_uids(uid_t **users);
+
+/* Monitor object */
+typedef struct sd_login_monitor sd_login_monitor;
+
+/* Create a new monitor. Category must be NULL, "seat", "session",
+ * "uid" to get monitor events for the specific category (or all). */
+int sd_login_monitor_new(const char *category, sd_login_monitor** ret);
+
+/* Destroys the passed monitor. Returns NULL. */
+sd_login_monitor* sd_login_monitor_unref(sd_login_monitor *m);
+
+/* Flushes the monitor */
+int sd_login_monitor_flush(sd_login_monitor *m);
+
+/* Get FD from monitor */
+int sd_login_monitor_get_fd(sd_login_monitor *m);
+
 #endif
diff --git a/src/test-login.c b/src/test-login.c
index 97313fcbcb..21cd3a1900 100644
--- a/src/test-login.c
+++ b/src/test-login.c
@@ -19,26 +19,54 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 ***/
 
+#include <sys/poll.h>
+#include <string.h>
+
 #include "sd-login.h"
 #include "util.h"
+#include "strv.h"
 
 int main(int argc, char* argv[]) {
-    int r, k;
-    uid_t u, u2;
+        int r, k;
+        uid_t u, u2;
         char *seat;
         char *session;
         char *state;
         char *session2;
+        char *t;
+        char **seats, **sessions;
+        uid_t *uids;
+        unsigned n;
+        struct pollfd pollfd;
+        sd_login_monitor *m;
 
         assert_se(sd_pid_get_session(0, &session) == 0);
         printf("session = %s\n", session);
 
+        assert_se(sd_pid_get_owner_uid(0, &u2) == 0);
+        printf("user = %lu\n", (unsigned long) u2);
+
+        r = sd_uid_get_sessions(u2, false, &sessions);
+        assert_se(r >= 0);
+        assert_se(t = strv_join(sessions, ", "));
+        strv_free(sessions);
+        printf("sessions = %s\n", t);
+        free(t);
+
+        r = sd_uid_get_seats(u2, false, &seats);
+        assert_se(r >= 0);
+        assert_se(t = strv_join(seats, ", "));
+        strv_free(seats);
+        printf("seats = %s\n", t);
+        free(t);
+
         r = sd_session_is_active(session);
         assert_se(r >= 0);
         printf("active = %s\n", yes_no(r));
 
         assert_se(sd_session_get_uid(session, &u) >= 0);
         printf("uid = %lu\n", (unsigned long) u);
+        assert_se(u == u2);
 
         assert_se(sd_session_get_seat(session, &seat) >= 0);
         printf("seat = %s\n", seat);
@@ -46,9 +74,9 @@ int main(int argc, char* argv[]) {
         assert_se(sd_uid_get_state(u, &state) >= 0);
         printf("state = %s\n", state);
 
-        assert_se(sd_uid_is_on_seat(u, seat) > 0);
+        assert_se(sd_uid_is_on_seat(u, 0, seat) > 0);
 
-        k = sd_uid_is_active_on_seat(u, seat);
+        k = sd_uid_is_on_seat(u, 1, seat);
         assert_se(k >= 0);
         assert_se(!!r == !!r);
 
@@ -56,10 +84,60 @@ int main(int argc, char* argv[]) {
         printf("session2 = %s\n", session2);
         printf("uid2 = %lu\n", (unsigned long) u2);
 
+        assert_se(sd_seat_get_sessions(seat, &sessions, &uids, &n) >= 0);
+        assert_se(t = strv_join(sessions, ", "));
+        strv_free(sessions);
+        printf("sessions = %s\n", t);
+        free(t);
+        printf("uids =");
+        for (k = 0; k < (int) n; k++)
+                printf(" %lu", (unsigned long) uids[k]);
+        printf("\n");
+        free(uids);
+
         free(session);
         free(state);
         free(session2);
         free(seat);
 
+        assert_se(sd_get_seats(&seats) >= 0);
+        assert_se(t = strv_join(seats, ", "));
+        strv_free(seats);
+        printf("seats = %s\n", t);
+        free(t);
+
+        assert_se(sd_get_sessions(&sessions) >= 0);
+        assert_se(t = strv_join(sessions, ", "));
+        strv_free(sessions);
+        printf("sessions = %s\n", t);
+        free(t);
+
+        r = sd_get_uids(&uids);
+        assert_se(r >= 0);
+
+        printf("uids =");
+        for (k = 0; k < r; k++)
+                printf(" %lu", (unsigned long) uids[k]);
+        printf("\n");
+
+        free(uids);
+
+        r = sd_login_monitor_new("session", &m);
+        assert_se(r >= 0);
+
+        zero(pollfd);
+        pollfd.fd = sd_login_monitor_get_fd(m);
+        pollfd.events = POLLIN;
+
+        for (n = 0; n < 5; n++) {
+                r = poll(&pollfd, 1, -1);
+                assert_se(r >= 0);
+
+                sd_login_monitor_flush(m);
+                printf("Wake!\n");
+        }
+
+        sd_login_monitor_unref(m);
+
         return 0;
 }
diff --git a/src/util.c b/src/util.c
index 328a1ead92..2d4f229193 100644
--- a/src/util.c
+++ b/src/util.c
@@ -317,6 +317,26 @@ int parse_pid(const char *s, pid_t* ret_pid) {
         return 0;
 }
 
+int parse_uid(const char *s, uid_t* ret_uid) {
+        unsigned long ul = 0;
+        uid_t uid;
+        int r;
+
+        assert(s);
+        assert(ret_uid);
+
+        if ((r = safe_atolu(s, &ul)) < 0)
+                return r;
+
+        uid = (uid_t) ul;
+
+        if ((unsigned long) uid != ul)
+                return -ERANGE;
+
+        *ret_uid = uid;
+        return 0;
+}
+
 int safe_atou(const char *s, unsigned *ret_u) {
         char *x = NULL;
         unsigned long l;
@@ -5357,6 +5377,70 @@ int in_search_path(const char *path, char **search) {
         return r;
 }
 
+int get_files_in_directory(const char *path, char ***list) {
+        DIR *d;
+        int r = 0;
+        unsigned n = 0;
+        char **l = NULL;
+
+        assert(path);
+        assert(list);
+
+        d = opendir(path);
+        for (;;) {
+                struct dirent buffer, *de;
+                int k;
+
+                k = readdir_r(d, &buffer, &de);
+                if (k != 0) {
+                        r = -k;
+                        goto finish;
+                }
+
+                if (!de)
+                        break;
+
+                dirent_ensure_type(d, de);
+
+                if (!dirent_is_file(de))
+                        continue;
+
+                if ((unsigned) r >= n) {
+                        char **t;
+
+                        n = MAX(16, 2*r);
+                        t = realloc(l, sizeof(char*) * n);
+                        if (!t) {
+                                r = -ENOMEM;
+                                goto finish;
+                        }
+
+                        l = t;
+                }
+
+                assert((unsigned) r < n);
+
+                l[r] = strdup(de->d_name);
+                if (!l[r]) {
+                        r = -ENOMEM;
+                        goto finish;
+                }
+
+                l[++r] = NULL;
+        }
+
+finish:
+        if (d)
+                closedir(d);
+
+        if (r >= 0)
+                *list = l;
+        else
+                strv_free(l);
+
+        return r;
+}
+
 static const char *const ioprio_class_table[] = {
         [IOPRIO_CLASS_NONE] = "none",
         [IOPRIO_CLASS_RT] = "realtime",
diff --git a/src/util.h b/src/util.h
index f39c01fbd7..9537d130d3 100644
--- a/src/util.h
+++ b/src/util.h
@@ -136,6 +136,8 @@ void close_many(const int fds[], unsigned n_fd);
 int parse_boolean(const char *v);
 int parse_usec(const char *t, usec_t *usec);
 int parse_pid(const char *s, pid_t* ret_pid);
+int parse_uid(const char *s, uid_t* ret_uid);
+#define parse_gid(s, ret_uid) parse_uid(s, ret_uid)
 
 int safe_atou(const char *s, unsigned *ret_u);
 int safe_atoi(const char *s, int *ret_i);
@@ -453,6 +455,7 @@ int glob_exists(const char *path);
 int dirent_ensure_type(DIR *d, struct dirent *de);
 
 int in_search_path(const char *path, char **search);
+int get_files_in_directory(const char *path, char ***list);
 
 #define NULSTR_FOREACH(i, l)                                    \
         for ((i) = (l); (i) && *(i); (i) = strchr((i), 0)+1)