core: add new logic for services to store file descriptors in PID 1

With this change it is possible to send file descriptors to PID 1, via
sd_pid_notify_with_fds() which PID 1 will store individually for each
service, and pass via the usual fd passing logic on next invocation.
This is useful for enable daemon reload schemes where daemons serialize
their state to /run, push their fds into PID 1 and terminate, restoring
their state on next start from the data in /run and passed in from PID
1.

The fds are kept by PID 1 as long as no POLLHUP or POLLERR is seen on
them, and the service they belong to are either not dead or failed, or
have a job queued.

18 files changed, 594 insertions, 100 deletions

diff --git a/Makefile-man.am b/Makefile-man.am
index 68e7483e70..8dc8febcf6 100644
--- a/Makefile-man.am
+++ b/Makefile-man.am
@@ -198,6 +198,9 @@ MANPAGES_ALIAS += \
 	man/sd_journal_wait.3 \
 	man/sd_machine_get_ifindices.3 \
 	man/sd_notifyf.3 \
+	man/sd_pid_notify.3 \
+	man/sd_pid_notify_with_fds.3 \
+	man/sd_pid_notifyf.3 \
 	man/sleep.conf.d.5 \
 	man/system.conf.d.5 \
 	man/systemd-ask-password-console.path.8 \
@@ -308,6 +311,9 @@ man/sd_journal_test_cursor.3: man/sd_journal_get_cursor.3
 man/sd_journal_wait.3: man/sd_journal_get_fd.3
 man/sd_machine_get_ifindices.3: man/sd_machine_get_class.3
 man/sd_notifyf.3: man/sd_notify.3
+man/sd_pid_notify.3: man/sd_notify.3
+man/sd_pid_notify_with_fds.3: man/sd_notify.3
+man/sd_pid_notifyf.3: man/sd_notify.3
 man/sleep.conf.d.5: man/systemd-sleep.conf.5
 man/system.conf.d.5: man/systemd-system.conf.5
 man/systemd-ask-password-console.path.8: man/systemd-ask-password-console.service.8
@@ -566,6 +572,15 @@ man/sd_machine_get_ifindices.html: man/sd_machine_get_class.html
 man/sd_notifyf.html: man/sd_notify.html
 	$(html-alias)
 
+man/sd_pid_notify.html: man/sd_notify.html
+	$(html-alias)
+
+man/sd_pid_notify_with_fds.html: man/sd_notify.html
+	$(html-alias)
+
+man/sd_pid_notifyf.html: man/sd_notify.html
+	$(html-alias)
+
 man/sleep.conf.d.html: man/systemd-sleep.conf.html
 	$(html-alias)
 
@@ -674,12 +689,6 @@ man/systemd-user.conf.html: man/systemd-system.conf.html
 man/user.conf.d.html: man/systemd-system.conf.html
 	$(html-alias)
 
-if ENABLE_HWDB
-MANPAGES += \
-        man/hwdb.7 \
-        man/systemd-hwdb.8
-
-endif
 
 if ENABLE_BACKLIGHT
 MANPAGES += \
@@ -750,6 +759,16 @@ man/systemd-hostnamed.html: man/systemd-hostnamed.service.html
 
 endif
 
+if ENABLE_HWDB
+MANPAGES += \
+	man/hwdb.7 \
+	man/systemd-hwdb.8
+MANPAGES_ALIAS += \
+	#
+
+
+endif
+
 if ENABLE_KDBUS
 MANPAGES += \
 	man/sd_bus_creds_get_pid.3 \
diff --git a/man/sd_listen_fds.xml b/man/sd_listen_fds.xml
index 6999db9804..4377745634 100644
--- a/man/sd_listen_fds.xml
+++ b/man/sd_listen_fds.xml
@@ -73,7 +73,7 @@
                 <para>If the <parameter>unset_environment</parameter>
                 parameter is non-zero,
                 <function>sd_listen_fds()</function> will unset the
-                <varname>$LISTEN_FDS</varname>/<varname>$LISTEN_PID</varname>
+                <varname>$LISTEN_FDS</varname> and <varname>$LISTEN_PID</varname>
                 environment variables before returning (regardless of
                 whether the function call itself succeeded or
                 not). Further calls to
@@ -83,10 +83,11 @@
 
                 <para>If a daemon receives more than one file
                 descriptor, they will be passed in the same order as
-                configured in the systemd socket definition
-                file. Nonetheless, it is recommended to verify the
-                correct socket types before using them. To simplify
-                this checking, the functions
+                configured in the systemd socket unit file (see
+                <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+                for details). Nonetheless, it is recommended to verify
+                the correct socket types before using them. To
+                simplify this checking, the functions
                 <citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                 <citerefentry><refentrytitle>sd_is_socket</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                 <citerefentry><refentrytitle>sd_is_socket_inet</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
@@ -103,6 +104,16 @@
                 <para>This function call will set the FD_CLOEXEC flag
                 for all passed file descriptors to avoid further
                 inheritance to children of the calling process.</para>
+
+                <para>If multiple socket units activate the same
+                service the order of the file descriptors passed to
+                its main process is undefined. If additional file
+                descriptors have been passed to the service manager
+                using
+                <citerefentry><refentrytitle>sd_pid_notify_with_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>'s
+                <literal>FDSTORE=1</literal> messages, these file
+                descriptors are passed last, in arbitrary order, and
+                with duplicates removed.</para>
         </refsect1>
 
         <refsect1>
diff --git a/man/sd_notify.xml b/man/sd_notify.xml
index 35f6f71ab3..2bf3383c0d 100644
--- a/man/sd_notify.xml
+++ b/man/sd_notify.xml
@@ -46,6 +46,9 @@
         <refnamediv>
                 <refname>sd_notify</refname>
                 <refname>sd_notifyf</refname>
+                <refname>sd_pid_notify</refname>
+                <refname>sd_pid_notifyf</refname>
+                <refname>sd_pid_notify_with_fds</refname>
                 <refpurpose>Notify service manager about start-up completion and other service status changes</refpurpose>
         </refnamediv>
 
@@ -65,6 +68,30 @@
                                 <paramdef>const char *<parameter>format</parameter></paramdef>
                                 <paramdef>...</paramdef>
                         </funcprototype>
+
+                        <funcprototype>
+                                <funcdef>int <function>sd_pid_notify</function></funcdef>
+                                <paramdef>pid_t <parameter>pid</parameter></paramdef>
+                                <paramdef>int <parameter>unset_environment</parameter></paramdef>
+                                <paramdef>const char *<parameter>state</parameter></paramdef>
+                        </funcprototype>
+
+                        <funcprototype>
+                                <funcdef>int <function>sd_pid_notifyf</function></funcdef>
+                                <paramdef>pid_t <parameter>pid</parameter></paramdef>
+                                <paramdef>int <parameter>unset_environment</parameter></paramdef>
+                                <paramdef>const char *<parameter>format</parameter></paramdef>
+                                <paramdef>...</paramdef>
+                        </funcprototype>
+
+                        <funcprototype>
+                                <funcdef>int <function>sd_pid_notify_with_fds</function></funcdef>
+                                <paramdef>pid_t <parameter>pid</parameter></paramdef>
+                                <paramdef>int <parameter>unset_environment</parameter></paramdef>
+                                <paramdef>const char *<parameter>state</parameter></paramdef>
+                                <paramdef>const int *<parameter>fds</parameter></paramdef>
+                                <paramdef>unsigned <parameter>n_fds</parameter></paramdef>
+                        </funcprototype>
                 </funcsynopsis>
         </refsynopsisdiv>
 
@@ -175,7 +202,7 @@
                         <varlistentry>
                                 <term>MAINPID=...</term>
 
-                                <listitem><para>The main pid of the
+                                <listitem><para>The main process ID (PID) of the
                                 service, in case the service manager did
                                 not fork off the process
                                 itself. Example:
@@ -185,7 +212,7 @@
                         <varlistentry>
                                 <term>WATCHDOG=1</term>
 
-                                <listitem><para>Tells systemd to
+                                <listitem><para>Tells the service manager to
                                 update the watchdog timestamp. This is
                                 the keep-alive ping that services need
                                 to issue in regular intervals if
@@ -199,12 +226,53 @@
                                 check if the the watchdog is enabled.
                                 </para></listitem>
                         </varlistentry>
+
+
+                        <varlistentry>
+                                <term>FDSTORE=1</term>
+
+                                <listitem><para>Stores additional file
+                                descriptors in the service
+                                manager. File descriptors sent this
+                                way will be maintained per-service by
+                                the service manager and be passed
+                                again using the usual file descriptor
+                                passing logic on the next invocation
+                                of the service (see
+                                <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>). This
+                                is useful for implementing service
+                                restart schemes where services
+                                serialize their state to
+                                <filename>/run</filename>, push their
+                                file descriptors to the system
+                                manager, and are then restarted,
+                                retrieving their state again via
+                                socket passing and
+                                <filename>/run</filename>. Note that
+                                the service manager will accept
+                                messages for a service only if
+                                <varname>FileDescriptorStoreMax=</varname>
+                                is set to non-zero for it (defaults to
+                                zero). See
+                                <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+                                for details. Multiple arrays of file
+                                descriptors may be sent in seperate
+                                messages, in which case the arrays are
+                                combined. Note that the service
+                                manager removes duplicate file
+                                descriptors before passing them to the
+                                service. Use
+                                <function>sd_pid_notify_with_fds()</function>
+                                to send messages with
+                                <literal>FDSTORE=1</literal>, see
+                                below.</para></listitem>
+                        </varlistentry>
+
                 </variablelist>
 
                 <para>It is recommended to prefix variable names that
-                are not shown in the list above with
-                <varname>X_</varname> to avoid namespace
-                clashes.</para>
+                are not listed above with <varname>X_</varname> to
+                avoid namespace clashes.</para>
 
                 <para>Note that systemd will accept status data sent
                 from a service only if the
@@ -217,6 +285,36 @@
                 <function>sd_notify()</function> but takes a
                 <function>printf()</function>-like format string plus
                 arguments.</para>
+
+                <para><function>sd_pid_notify()</function> and
+                <function>sd_pid_notifyf()</function> are similar to
+                <function>sd_notify()</function> and
+                <function>sd_notifyf()</function> but take a process
+                ID (PID) to use as originating PID for the message as
+                first argument. This is useful to send notification
+                messages on behalf of other processes, provided the
+                appropriate privileges are available. If the PID
+                argument is specified as 0 the process ID of the
+                calling process is used, in which case the calls are
+                fully equivalent to <function>sd_notify()</function>
+                and <function>sd_notifyf()</function>.</para>
+
+                <para><function>sd_pid_notify_with_fds()</function> is
+                similar to <function>sd_pid_notify()</function> but
+                takes an additional array of file descriptors. These
+                file descriptors are sent along the notification
+                message to the service manager. This is particularly
+                useful for sending <literal>FDSTORE=1</literal>
+                messages, as described above. The additional arguments
+                are a pointer to the file descriptor array plus the
+                number of file descriptors in the array. If the number
+                of file descriptors is passed as 0, the call is fully
+                equivalent to <function>sd_pid_notify()</function>,
+                i.e. no file descriptors are passed. Note that sending
+                file descriptors to the service manager on messages
+                that do not expect them (i.e. without
+                <literal>FDSTORE=1</literal>) they are immediately
+                closed on reception.</para>
         </refsect1>
 
         <refsect1>
@@ -295,13 +393,25 @@
                 <example>
                         <title>Error Cause Notification</title>
 
-                        <para>A service could send the following shortly before exiting, on failure</para>
+                        <para>A service could send the following shortly before exiting, on failure:</para>
 
                         <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
               "ERRNO=%i",
               strerror(errno),
               errno);</programlisting>
                 </example>
+
+                <example>
+                        <title>Store a File Descriptor in the Service Manager</title>
+
+                        <para>To store an open file descriptor in the
+                        service manager, in order to continue
+                        operation after a service restart without
+                        losing state use
+                        <literal>FDSTORE=1</literal>:</para>
+
+                        <programlisting>sd_pid_notify_with_fds(0, 0, "FDSTORE=1", &amp;fd, 1);</programlisting>
+                </example>
         </refsect1>
 
         <refsect1>
diff --git a/man/systemd.service.xml b/man/systemd.service.xml
index 0b68aa0890..4c890dfb7b 100644
--- a/man/systemd.service.xml
+++ b/man/systemd.service.xml
@@ -1117,6 +1117,35 @@
                                 command.</para></listitem>
                         </varlistentry>
 
+                        <varlistentry>
+                                <term><varname>FileDescriptorStoreMax=</varname></term>
+                                <listitem><para>Configure how many
+                                file descriptors may be stored in the
+                                service manager for the service using
+                                <citerefentry><refentrytitle>sd_pid_notify_with_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>'s
+                                <literal>FDSTORE=1</literal>
+                                messages. This is useful for
+                                implementing service restart schemes
+                                where the state is serialized to
+                                <filename>/run</filename> and the file
+                                descriptors passed to the service
+                                manager, to allow restarts without
+                                losing state. Defaults to 0, i.e. no
+                                file descriptors may be stored in the
+                                service manager by default. All file
+                                descriptors passed to the service
+                                manager from a specific service are
+                                passed back to the service's main
+                                process on the next service
+                                restart. Any file descriptors passed
+                                to the service manager are
+                                automatically closed when POLLHUP or
+                                POLLERR is seen on them, or when the
+                                service is fully stopped and no job
+                                queued or being executed for
+                                it.</para></listitem>
+                        </varlistentry>
+
                 </variablelist>
 
                 <para>Check
diff --git a/src/core/dbus-service.c b/src/core/dbus-service.c
index 2b50ac93d8..6d4713babc 100644
--- a/src/core/dbus-service.c
+++ b/src/core/dbus-service.c
@@ -59,6 +59,7 @@ const sd_bus_vtable bus_service_vtable[] = {
         SD_BUS_PROPERTY("MainPID", "u", bus_property_get_pid, offsetof(Service, main_pid), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("ControlPID", "u", bus_property_get_pid, offsetof(Service, control_pid), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("BusName", "s", NULL, offsetof(Service, bus_name), SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("FileDescriptorStoreMax", "u", NULL, offsetof(Service, n_fd_store_max), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("StatusText", "s", NULL, offsetof(Service, status_text), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("StatusErrno", "i", NULL, offsetof(Service, status_errno), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("Result", "s", property_get_result, offsetof(Service, result), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
diff --git a/src/core/load-fragment-gperf.gperf.m4 b/src/core/load-fragment-gperf.gperf.m4
index e0ffaa605a..9e87d91e77 100644
--- a/src/core/load-fragment-gperf.gperf.m4
+++ b/src/core/load-fragment-gperf.gperf.m4
@@ -226,6 +226,7 @@ Service.SuccessExitStatus,       config_parse_set_status,            0,
 Service.SysVStartPriority,       config_parse_warn_compat,           DISABLED_LEGACY,               0
 Service.NonBlocking,             config_parse_bool,                  0,                             offsetof(Service, exec_context.non_blocking)
 Service.BusName,                 config_parse_unit_string_printf,    0,                             offsetof(Service, bus_name)
+Service.FileDescriptorStoreMax,  config_parse_unsigned,              0,                             offsetof(Service, n_fd_store_max)
 Service.NotifyAccess,            config_parse_notify_access,         0,                             offsetof(Service, notify_access)
 Service.Sockets,                 config_parse_service_sockets,       0,                             0
 m4_ifdef(`ENABLE_KDBUS',
diff --git a/src/core/manager.c b/src/core/manager.c
index 519b374382..c18312a369 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -84,6 +84,9 @@
 #define JOBS_IN_PROGRESS_PERIOD_USEC (USEC_PER_SEC / 3)
 #define JOBS_IN_PROGRESS_PERIOD_DIVISOR 3
 
+#define NOTIFY_FD_MAX 768
+#define NOTIFY_BUFFER_MAX PIPE_BUF
+
 static int manager_dispatch_notify_fd(sd_event_source *source, int fd, uint32_t revents, void *userdata);
 static int manager_dispatch_signal_fd(sd_event_source *source, int fd, uint32_t revents, void *userdata);
 static int manager_dispatch_time_change_fd(sd_event_source *source, int fd, uint32_t revents, void *userdata);
@@ -1449,7 +1452,7 @@ static unsigned manager_dispatch_dbus_queue(Manager *m) {
         return n;
 }
 
-static void manager_invoke_notify_message(Manager *m, Unit *u, pid_t pid, char *buf, size_t n) {
+static void manager_invoke_notify_message(Manager *m, Unit *u, pid_t pid, char *buf, size_t n, FDSet *fds) {
         _cleanup_strv_free_ char **tags = NULL;
 
         assert(m);
@@ -1466,12 +1469,13 @@ static void manager_invoke_notify_message(Manager *m, Unit *u, pid_t pid, char *
         log_unit_debug(u->id, "Got notification message for unit %s", u->id);
 
         if (UNIT_VTABLE(u)->notify_message)
-                UNIT_VTABLE(u)->notify_message(u, pid, tags);
+                UNIT_VTABLE(u)->notify_message(u, pid, tags, fds);
 }
 
 static int manager_dispatch_notify_fd(sd_event_source *source, int fd, uint32_t revents, void *userdata) {
         Manager *m = userdata;
         ssize_t n;
+        int r;
 
         assert(m);
         assert(m->notify_fd == fd);
@@ -1482,73 +1486,101 @@ static int manager_dispatch_notify_fd(sd_event_source *source, int fd, uint32_t
         }
 
         for (;;) {
-                char buf[4096];
+                _cleanup_fdset_free_ FDSet *fds = NULL;
+                char buf[NOTIFY_BUFFER_MAX+1];
                 struct iovec iovec = {
                         .iov_base = buf,
                         .iov_len = sizeof(buf)-1,
                 };
-                bool found = false;
-
                 union {
                         struct cmsghdr cmsghdr;
-                        uint8_t buf[CMSG_SPACE(sizeof(struct ucred))];
+                        uint8_t buf[CMSG_SPACE(sizeof(struct ucred)) +
+                                    CMSG_SPACE(sizeof(int) * NOTIFY_FD_MAX)];
                 } control = {};
-
                 struct msghdr msghdr = {
                         .msg_iov = &iovec,
                         .msg_iovlen = 1,
                         .msg_control = &control,
                         .msg_controllen = sizeof(control),
                 };
-                struct ucred *ucred;
+                struct cmsghdr *cmsg;
+                struct ucred *ucred = NULL;
+                bool found = false;
                 Unit *u1, *u2, *u3;
+                int *fd_array = NULL;
+                unsigned n_fds = 0;
 
-                n = recvmsg(m->notify_fd, &msghdr, MSG_DONTWAIT);
-                if (n <= 0) {
-                        if (n == 0)
-                                return -EIO;
-
+                n = recvmsg(m->notify_fd, &msghdr, MSG_DONTWAIT|MSG_CMSG_CLOEXEC);
+                if (n < 0) {
                         if (errno == EAGAIN || errno == EINTR)
                                 break;
 
                         return -errno;
                 }
+                if (n == 0)
+                        return -ECONNRESET;
+
+                for (cmsg = CMSG_FIRSTHDR(&msghdr); cmsg; cmsg = CMSG_NXTHDR(&msghdr, cmsg)) {
+                        if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_RIGHTS) {
+
+                                fd_array = (int*) CMSG_DATA(cmsg);
+                                n_fds = (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int);
+
+                        } else if (cmsg->cmsg_level == SOL_SOCKET &&
+                                   cmsg->cmsg_type == SCM_CREDENTIALS &&
+                                   cmsg->cmsg_len == CMSG_LEN(sizeof(struct ucred))) {
 
-                if (msghdr.msg_controllen < CMSG_LEN(sizeof(struct ucred)) ||
-                    control.cmsghdr.cmsg_level != SOL_SOCKET ||
-                    control.cmsghdr.cmsg_type != SCM_CREDENTIALS ||
-                    control.cmsghdr.cmsg_len != CMSG_LEN(sizeof(struct ucred))) {
-                        log_warning("Received notify message without credentials. Ignoring.");
+                                ucred = (struct ucred*) CMSG_DATA(cmsg);
+                        }
+                }
+
+                if (n_fds > 0) {
+                        assert(fd_array);
+
+                        r = fdset_new_array(&fds, fd_array, n_fds);
+                        if (r < 0) {
+                                close_many(fd_array, n_fds);
+                                return log_oom();
+                        }
+                }
+
+                if (!ucred || ucred->pid <= 0) {
+                        log_warning("Received notify message without valid credentials. Ignoring.");
                         continue;
                 }
 
-                ucred = (struct ucred*) CMSG_DATA(&control.cmsghdr);
+                if ((size_t) n >= sizeof(buf)) {
+                        log_warning("Received notify message exceeded maximum size. Ignoring.");
+                        continue;
+                }
 
-                assert((size_t) n < sizeof(buf));
                 buf[n] = 0;
 
                 /* Notify every unit that might be interested, but try
                  * to avoid notifying the same one multiple times. */
                 u1 = manager_get_unit_by_pid(m, ucred->pid);
                 if (u1) {
-                        manager_invoke_notify_message(m, u1, ucred->pid, buf, n);
+                        manager_invoke_notify_message(m, u1, ucred->pid, buf, n, fds);
                         found = true;
                 }
 
                 u2 = hashmap_get(m->watch_pids1, LONG_TO_PTR(ucred->pid));
                 if (u2 && u2 != u1) {
-                        manager_invoke_notify_message(m, u2, ucred->pid, buf, n);
+                        manager_invoke_notify_message(m, u2, ucred->pid, buf, n, fds);
                         found = true;
                 }
 
                 u3 = hashmap_get(m->watch_pids2, LONG_TO_PTR(ucred->pid));
                 if (u3 && u3 != u2 && u3 != u1) {
-                        manager_invoke_notify_message(m, u3, ucred->pid, buf, n);
+                        manager_invoke_notify_message(m, u3, ucred->pid, buf, n, fds);
                         found = true;
                 }
 
                 if (!found)
                         log_warning("Cannot find unit for notify message of PID "PID_FMT".", ucred->pid);
+
+                if (fdset_size(fds) > 0)
+                        log_warning("Got auxiliary fds with notification message, closing all.");
         }
 
         return 0;
diff --git a/src/core/service.c b/src/core/service.c
index bfbe959edb..78232ee71c 100644
--- a/src/core/service.c
+++ b/src/core/service.c
@@ -242,6 +242,42 @@ static void service_reset_watchdog(Service *s) {
         service_start_watchdog(s);
 }
 
+static void service_fd_store_unlink(ServiceFDStore *fs) {
+
+        if (!fs)
+                return;
+
+        if (fs->service) {
+                assert(fs->service->n_fd_store > 0);
+                LIST_REMOVE(fd_store, fs->service->fd_store, fs);
+                fs->service->n_fd_store--;
+        }
+
+        if (fs->event_source) {
+                sd_event_source_set_enabled(fs->event_source, SD_EVENT_OFF);
+                sd_event_source_unref(fs->event_source);
+        }
+
+        safe_close(fs->fd);
+        free(fs);
+}
+
+static void service_release_resources(Unit *u) {
+        Service *s = SERVICE(u);
+
+        assert(s);
+
+        if (!s->fd_store)
+                return;
+
+        log_debug("Releasing all resources for %s", u->id);
+
+        while (s->fd_store)
+                service_fd_store_unlink(s->fd_store);
+
+        assert(s->n_fd_store == 0);
+}
+
 static void service_done(Unit *u) {
         Service *s = SERVICE(u);
 
@@ -286,6 +322,8 @@ static void service_done(Unit *u) {
         service_stop_watchdog(s);
 
         s->timer_event_source = sd_event_source_unref(s->timer_event_source);
+
+        service_release_resources(u);
 }
 
 static int service_arm_timer(Service *s, usec_t usec) {
@@ -549,6 +587,14 @@ static void service_dump(Unit *u, FILE *f, const char *prefix) {
         if (s->status_text)
                 fprintf(f, "%sStatus Text: %s\n",
                         prefix, s->status_text);
+
+        if (s->n_fd_store_max > 0) {
+                fprintf(f,
+                        "%sFile Descriptor Store Max: %u\n"
+                        "%sFile Descriptor Store Current: %u\n",
+                        prefix, s->n_fd_store_max,
+                        prefix, s->n_fd_store);
+        }
 }
 
 static int service_load_pid_file(Service *s, bool may_warn) {
@@ -806,10 +852,10 @@ static int service_coldplug(Unit *u) {
 }
 
 static int service_collect_fds(Service *s, int **fds, unsigned *n_fds) {
+        _cleanup_free_ int *rfds = NULL;
+        unsigned rn_fds = 0;
         Iterator i;
         int r;
-        int *rfds = NULL;
-        unsigned rn_fds = 0;
         Unit *u;
 
         assert(s);
@@ -831,10 +877,12 @@ static int service_collect_fds(Service *s, int **fds, unsigned *n_fds) {
 
                 r = socket_collect_fds(sock, &cfds, &cn_fds);
                 if (r < 0)
-                        goto fail;
+                        return r;
 
-                if (!cfds)
+                if (cn_fds <= 0) {
+                        free(cfds);
                         continue;
+                }
 
                 if (!rfds) {
                         rfds = cfds;
@@ -842,32 +890,39 @@ static int service_collect_fds(Service *s, int **fds, unsigned *n_fds) {
                 } else {
                         int *t;
 
-                        t = new(int, rn_fds+cn_fds);
+                        t = realloc(rfds, (rn_fds + cn_fds) * sizeof(int));
                         if (!t) {
                                 free(cfds);
-                                r = -ENOMEM;
-                                goto fail;
+                                return -ENOMEM;
                         }
 
-                        memcpy(t, rfds, rn_fds * sizeof(int));
-                        memcpy(t+rn_fds, cfds, cn_fds * sizeof(int));
-                        free(rfds);
+                        memcpy(t + rn_fds, cfds, cn_fds * sizeof(int));
+                        rfds = t;
+                        rn_fds += cn_fds;
+
                         free(cfds);
 
-                        rfds = t;
-                        rn_fds = rn_fds+cn_fds;
                 }
         }
 
+        if (s->n_fd_store > 0) {
+                ServiceFDStore *fs;
+                int *t;
+
+                t = realloc(rfds, (rn_fds + s->n_fd_store) * sizeof(int));
+                if (!t)
+                        return -ENOMEM;
+
+                rfds = t;
+                LIST_FOREACH(fd_store, fs, s->fd_store)
+                        rfds[rn_fds++] = fs->fd;
+        }
+
         *fds = rfds;
         *n_fds = rn_fds;
 
+        rfds = NULL;
         return 0;
-
-fail:
-        free(rfds);
-
-        return r;
 }
 
 static int service_spawn(
@@ -2543,7 +2598,75 @@ static int service_dispatch_watchdog(sd_event_source *source, usec_t usec, void
         return 0;
 }
 
-static void service_notify_message(Unit *u, pid_t pid, char **tags) {
+static int on_fd_store_io(sd_event_source *e, int fd, uint32_t revents, void *userdata) {
+        ServiceFDStore *fs = userdata;
+
+        assert(e);
+        assert(fs);
+
+        /* If we get either EPOLLHUP or EPOLLERR, it's time to remove this entry from the fd store */
+        service_fd_store_unlink(fs);
+        return 0;
+}
+
+static int service_add_fd_set(Service *s, FDSet *fds) {
+        int r;
+
+        assert(s);
+
+        if (fdset_size(fds) <= 0)
+                return 0;
+
+        while (s->n_fd_store < s->n_fd_store_max) {
+                _cleanup_close_ int fd = -1;
+                ServiceFDStore *fs;
+                bool same = false;
+
+                fd = fdset_steal_first(fds);
+                if (fd < 0)
+                        break;
+
+                LIST_FOREACH(fd_store, fs, s->fd_store) {
+                        r = same_fd(fs->fd, fd);
+                        if (r < 0)
+                                return log_unit_error_errno(UNIT(s)->id, r, "%s: Couldn't check if same fd: %m", UNIT(s)->id);
+                        if (r > 0) {
+                                same = true;
+                                break;
+                        }
+                }
+
+                if (same)
+                        continue;
+
+                fs = new0(ServiceFDStore, 1);
+                if (!fs)
+                        return log_oom();
+
+                fs->fd = fd;
+                fs->service = s;
+
+                r = sd_event_add_io(UNIT(s)->manager->event, &fs->event_source, fd, 0, on_fd_store_io, fs);
+                if (r < 0) {
+                        free(fs);
+                        return log_unit_error_errno(UNIT(s)->id, r, "%s: Failed to add even source: %m", UNIT(s)->id);
+                }
+
+                LIST_PREPEND(fd_store, s->fd_store, fs);
+                s->n_fd_store++;
+
+                fd = -1;
+
+                log_unit_debug(UNIT(s)->id, "%s: added fd to fd store.", UNIT(s)->id);
+        }
+
+        if (fdset_size(fds) > 0)
+                log_unit_warning(UNIT(s)->id, "%s: tried to store more fds than FDStoreMax=%u allows, closing remaining.", UNIT(s)->id, s->n_fd_store_max);
+
+        return 0;
+}
+
+static void service_notify_message(Unit *u, pid_t pid, char **tags, FDSet *fds) {
         Service *s = SERVICE(u);
         _cleanup_free_ char *cc = NULL;
         bool notify_dbus = false;
@@ -2675,6 +2798,12 @@ static void service_notify_message(Unit *u, pid_t pid, char **tags) {
                 service_reset_watchdog(s);
         }
 
+        /* Add the passed fds to the fd store */
+        if (strv_find(tags, "FDSTORE=1")) {
+                log_unit_debug(u->id, "%s: got FDSTORE=1", u->id);
+                service_add_fd_set(s, fds);
+        }
+
         /* Notify clients about changed status or main pid */
         if (notify_dbus)
                 unit_add_to_dbus_queue(u);
@@ -2917,6 +3046,7 @@ const UnitVTable service_vtable = {
         .init = service_init,
         .done = service_done,
         .load = service_load,
+        .release_resources = service_release_resources,
 
         .coldplug = service_coldplug,
 
diff --git a/src/core/service.h b/src/core/service.h
index f6a78c403b..dfeee6a68c 100644
--- a/src/core/service.h
+++ b/src/core/service.h
@@ -22,6 +22,7 @@
 ***/
 
 typedef struct Service Service;
+typedef struct ServiceFDStore ServiceFDStore;
 
 #include "unit.h"
 #include "path.h"
@@ -115,6 +116,15 @@ typedef enum ServiceResult {
         _SERVICE_RESULT_INVALID = -1
 } ServiceResult;
 
+struct ServiceFDStore {
+        Service *service;
+
+        int fd;
+        sd_event_source *event_source;
+
+        LIST_FIELDS(ServiceFDStore, fd_store);
+};
+
 struct Service {
         Unit meta;
 
@@ -198,6 +208,10 @@ struct Service {
 
         NotifyAccess notify_access;
         NotifyState notify_state;
+
+        ServiceFDStore *fd_store;
+        unsigned n_fd_store;
+        unsigned n_fd_store_max;
 };
 
 extern const UnitVTable service_vtable;
diff --git a/src/core/unit.c b/src/core/unit.c
index 229bd0f73a..7311c5804d 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -278,21 +278,32 @@ int unit_set_description(Unit *u, const char *description) {
 }
 
 bool unit_check_gc(Unit *u) {
+        UnitActiveState state;
         assert(u);
 
-        if (UNIT_VTABLE(u)->no_gc)
+        if (u->job)
                 return true;
 
-        if (u->no_gc)
+        if (u->nop_job)
                 return true;
 
-        if (u->job)
+        state = unit_active_state(u);
+
+        /* If the unit is inactive and failed and no job is queued for
+         * it, then release its runtime resources */
+        if (UNIT_IS_INACTIVE_OR_FAILED(state) &&
+            UNIT_VTABLE(u)->release_resources)
+                UNIT_VTABLE(u)->release_resources(u);
+
+        /* But we keep the unit object around for longer when it is
+         * referenced or configured to not be gc'ed */
+        if (state != UNIT_INACTIVE)
                 return true;
 
-        if (u->nop_job)
+        if (UNIT_VTABLE(u)->no_gc)
                 return true;
 
-        if (unit_active_state(u) != UNIT_INACTIVE)
+        if (u->no_gc)
                 return true;
 
         if (u->refs)
diff --git a/src/core/unit.h b/src/core/unit.h
index 19fa2f0585..53b8a7f66b 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -345,6 +345,10 @@ struct UnitVTable {
          * way */
         bool (*check_gc)(Unit *u);
 
+        /* When the unit is not running and no job for it queued we
+         * shall release its runtime resources */
+        void (*release_resources)(Unit *u);
+
         /* Return true when this unit is suitable for snapshotting */
         bool (*check_snapshot)(Unit *u);
 
@@ -359,7 +363,7 @@ struct UnitVTable {
         void (*notify_cgroup_empty)(Unit *u);
 
         /* Called whenever a process of this unit sends us a message */
-        void (*notify_message)(Unit *u, pid_t pid, char **tags);
+        void (*notify_message)(Unit *u, pid_t pid, char **tags, FDSet *fds);
 
         /* Called whenever a name this Unit registered for comes or
          * goes away. */
diff --git a/src/libsystemd/libsystemd.sym.m4 b/src/libsystemd/libsystemd.sym.m4
index 80a61baab8..19a49f45da 100644
--- a/src/libsystemd/libsystemd.sym.m4
+++ b/src/libsystemd/libsystemd.sym.m4
@@ -158,6 +158,11 @@ global:
         sd_session_get_desktop;
 } LIBSYSTEMD_216;
 
+LIBSYSTEMD_219 {
+global:
+        sd_pid_notify_with_fds;
+} LIBSYSTEMD_217;
+
 m4_ifdef(`ENABLE_KDBUS',
 LIBSYSTEMD_FUTURE {
 global:
diff --git a/src/libsystemd/sd-daemon/sd-daemon.c b/src/libsystemd/sd-daemon/sd-daemon.c
index 1f2a53393f..028c2a7a5b 100644
--- a/src/libsystemd/sd-daemon/sd-daemon.c
+++ b/src/libsystemd/sd-daemon/sd-daemon.c
@@ -340,16 +340,28 @@ _public_ int sd_is_mq(int fd, const char *path) {
         return 1;
 }
 
-_public_ int sd_pid_notify(pid_t pid, int unset_environment, const char *state) {
-        union sockaddr_union sockaddr = {};
-        _cleanup_close_ int fd = -1;
-        struct msghdr msghdr = {};
-        struct iovec iovec = {};
-        const char *e;
+_public_ int sd_pid_notify_with_fds(pid_t pid, int unset_environment, const char *state, const int *fds, unsigned n_fds) {
+        union sockaddr_union sockaddr = {
+                .sa.sa_family = AF_UNIX,
+        };
+        struct iovec iovec = {
+                .iov_base = (char*) state,
+        };
+        struct msghdr msghdr = {
+                .msg_iov = &iovec,
+                .msg_iovlen = 1,
+                .msg_name = &sockaddr,
+        };
         union {
                 struct cmsghdr cmsghdr;
-                uint8_t buf[CMSG_SPACE(sizeof(struct ucred))];
-        } control = {};
+                uint8_t buf[CMSG_SPACE(sizeof(struct ucred)) +
+                            CMSG_SPACE(sizeof(int) * n_fds)];
+        } control;
+        _cleanup_close_ int fd = -1;
+        struct cmsghdr *cmsg = NULL;
+        const char *e;
+        size_t controllen_without_ucred = 0;
+        bool try_without_ucred = false;
         int r;
 
         if (!state) {
@@ -357,6 +369,11 @@ _public_ int sd_pid_notify(pid_t pid, int unset_environment, const char *state)
                 goto finish;
         }
 
+        if (n_fds > 0 && !fds) {
+                r = -EINVAL;
+                goto finish;
+        }
+
         e = getenv("NOTIFY_SOCKET");
         if (!e)
                 return 0;
@@ -373,42 +390,50 @@ _public_ int sd_pid_notify(pid_t pid, int unset_environment, const char *state)
                 goto finish;
         }
 
-        sockaddr.sa.sa_family = AF_UNIX;
-        strncpy(sockaddr.un.sun_path, e, sizeof(sockaddr.un.sun_path));
+        iovec.iov_len = strlen(state);
 
+        strncpy(sockaddr.un.sun_path, e, sizeof(sockaddr.un.sun_path));
         if (sockaddr.un.sun_path[0] == '@')
                 sockaddr.un.sun_path[0] = 0;
 
-        iovec.iov_base = (char*) state;
-        iovec.iov_len = strlen(state);
-
-        msghdr.msg_name = &sockaddr;
         msghdr.msg_namelen = offsetof(struct sockaddr_un, sun_path) + strlen(e);
-
         if (msghdr.msg_namelen > sizeof(struct sockaddr_un))
                 msghdr.msg_namelen = sizeof(struct sockaddr_un);
 
-        msghdr.msg_iov = &iovec;
-        msghdr.msg_iovlen = 1;
+        if (n_fds > 0) {
+                msghdr.msg_control = &control;
+                msghdr.msg_controllen = CMSG_LEN(sizeof(int) * n_fds);
+
+                cmsg = CMSG_FIRSTHDR(&msghdr);
+                cmsg->cmsg_level = SOL_SOCKET;
+                cmsg->cmsg_type = SCM_RIGHTS;
+                cmsg->cmsg_len = CMSG_LEN(sizeof(int) * n_fds);
+
+                memcpy(CMSG_DATA(cmsg), fds, sizeof(int) * n_fds);
+        }
 
         if (pid != 0 && pid != getpid()) {
-                struct cmsghdr *cmsg;
-                struct ucred ucred = {};
+                struct ucred *ucred;
+
+                try_without_ucred = true;
+                controllen_without_ucred = msghdr.msg_controllen;
 
                 msghdr.msg_control = &control;
-                msghdr.msg_controllen = sizeof(control);
+                msghdr.msg_controllen += CMSG_LEN(sizeof(struct ucred));
+
+                if (cmsg)
+                        cmsg = CMSG_NXTHDR(&msghdr, cmsg);
+                else
+                        cmsg = CMSG_FIRSTHDR(&msghdr);
 
-                cmsg = CMSG_FIRSTHDR(&msghdr);
                 cmsg->cmsg_level = SOL_SOCKET;
                 cmsg->cmsg_type = SCM_CREDENTIALS;
                 cmsg->cmsg_len = CMSG_LEN(sizeof(struct ucred));
 
-                ucred.pid = pid;
-                ucred.uid = getuid();
-                ucred.gid = getgid();
-
-                memcpy(CMSG_DATA(cmsg), &ucred, sizeof(struct ucred));
-                msghdr.msg_controllen = cmsg->cmsg_len;
+                ucred = (struct ucred*) CMSG_DATA(cmsg);
+                ucred->pid = pid;
+                ucred->uid = getuid();
+                ucred->gid = getgid();
         }
 
         /* First try with fake ucred data, as requested */
@@ -417,10 +442,11 @@ _public_ int sd_pid_notify(pid_t pid, int unset_environment, const char *state)
                 goto finish;
         }
 
-        /* If that failed, try with our own instead */
-        if (msghdr.msg_control) {
-                msghdr.msg_control = NULL;
-                msghdr.msg_controllen = 0;
+        /* If that failed, try with our own ucred instead */
+        if (try_without_ucred) {
+                if (controllen_without_ucred <= 0)
+                        msghdr.msg_control = NULL;
+                msghdr.msg_controllen = controllen_without_ucred;
 
                 if (sendmsg(fd, &msghdr, MSG_NOSIGNAL) >= 0) {
                         r = 1;
@@ -437,8 +463,12 @@ finish:
         return r;
 }
 
+_public_ int sd_pid_notify(pid_t pid, int unset_environment, const char *state) {
+        return sd_pid_notify_with_fds(pid, unset_environment, state, NULL, 0);
+}
+
 _public_ int sd_notify(int unset_environment, const char *state) {
-        return sd_pid_notify(0, unset_environment, state);
+        return sd_pid_notify_with_fds(0, unset_environment, state, NULL, 0);
 }
 
 _public_ int sd_pid_notifyf(pid_t pid, int unset_environment, const char *format, ...) {
diff --git a/src/shared/fdset.c b/src/shared/fdset.c
index 46f7773a9e..9e35ce5cec 100644
--- a/src/shared/fdset.c
+++ b/src/shared/fdset.c
@@ -41,7 +41,31 @@ FDSet *fdset_new(void) {
         return MAKE_FDSET(set_new(NULL));
 }
 
-void fdset_free(FDSet *s) {
+int fdset_new_array(FDSet **ret, int *fds, unsigned n_fds) {
+        unsigned i;
+        FDSet *s;
+        int r;
+
+        assert(ret);
+
+        s = fdset_new();
+        if (!s)
+                return -ENOMEM;
+
+        for (i = 0; i < n_fds; i++) {
+
+                r = fdset_put(s, fds[i]);
+                if (r < 0) {
+                        set_free(MAKE_SET(s));
+                        return r;
+                }
+        }
+
+        *ret = s;
+        return 0;
+}
+
+FDSet* fdset_free(FDSet *s) {
         void *p;
 
         while ((p = set_steal_first(MAKE_SET(s)))) {
@@ -61,6 +85,7 @@ void fdset_free(FDSet *s) {
         }
 
         set_free(MAKE_SET(s));
+        return NULL;
 }
 
 int fdset_put(FDSet *s, int fd) {
@@ -70,6 +95,19 @@ int fdset_put(FDSet *s, int fd) {
         return set_put(MAKE_SET(s), FD_TO_PTR(fd));
 }
 
+int fdset_consume(FDSet *s, int fd) {
+        int r;
+
+        assert(s);
+        assert(fd >= 0);
+
+        r = fdset_put(s, fd);
+        if (r <= 0)
+                safe_close(fd);
+
+        return r;
+}
+
 int fdset_put_dup(FDSet *s, int fd) {
         int copy, r;
 
@@ -223,6 +261,10 @@ unsigned fdset_size(FDSet *fds) {
         return set_size(MAKE_SET(fds));
 }
 
+bool fdset_isempty(FDSet *fds) {
+        return set_isempty(MAKE_SET(fds));
+}
+
 int fdset_iterate(FDSet *s, Iterator *i) {
         void *p;
 
@@ -232,3 +274,13 @@ int fdset_iterate(FDSet *s, Iterator *i) {
 
         return PTR_TO_FD(p);
 }
+
+int fdset_steal_first(FDSet *fds) {
+        void *p;
+
+        p = set_steal_first(MAKE_SET(fds));
+        if (!p)
+                return -ENOENT;
+
+        return PTR_TO_FD(p);
+}
diff --git a/src/shared/fdset.h b/src/shared/fdset.h
index 907acd76dd..c3c5e52286 100644
--- a/src/shared/fdset.h
+++ b/src/shared/fdset.h
@@ -27,25 +27,30 @@
 typedef struct FDSet FDSet;
 
 FDSet* fdset_new(void);
-void fdset_free(FDSet *s);
+FDSet* fdset_free(FDSet *s);
 
 int fdset_put(FDSet *s, int fd);
 int fdset_put_dup(FDSet *s, int fd);
+int fdset_consume(FDSet *s, int fd);
 
 bool fdset_contains(FDSet *s, int fd);
 int fdset_remove(FDSet *s, int fd);
 
-int fdset_new_fill(FDSet **_s);
-int fdset_new_listen_fds(FDSet **_s, bool unset);
+int fdset_new_array(FDSet **ret, int *fds, unsigned n_fds);
+int fdset_new_fill(FDSet **ret);
+int fdset_new_listen_fds(FDSet **ret, bool unset);
 
 int fdset_cloexec(FDSet *fds, bool b);
 
 int fdset_close_others(FDSet *fds);
 
 unsigned fdset_size(FDSet *fds);
+bool fdset_isempty(FDSet *fds);
 
 int fdset_iterate(FDSet *s, Iterator *i);
 
+int fdset_steal_first(FDSet *fds);
+
 #define FDSET_FOREACH(fd, fds, i) \
         for ((i) = ITERATOR_FIRST, (fd) = fdset_iterate((fds), &(i)); (fd) >= 0; (fd) = fdset_iterate((fds), &(i)))
 
diff --git a/src/shared/util.c b/src/shared/util.c
index bda3c93ae3..f01022ed0b 100644
--- a/src/shared/util.c
+++ b/src/shared/util.c
@@ -7672,3 +7672,28 @@ int fd_setcrtime(int fd, usec_t usec) {
 
         return 0;
 }
+
+int same_fd(int a, int b) {
+        struct stat sta, stb;
+
+        assert(a >= 0);
+        assert(b >= 0);
+
+        if (a == b)
+                return true;
+
+        if (fstat(a, &sta) < 0)
+                return -errno;
+
+        if (fstat(b, &stb) < 0)
+                return -errno;
+
+        if ((sta.st_mode & S_IFMT) != (stb.st_mode & S_IFMT))
+                return false;
+
+        if (S_ISREG(sta.st_mode) || S_ISDIR(sta.st_mode) || S_ISFIFO(sta.st_mode) || S_ISSOCK(sta.st_mode) || S_ISLNK(sta.st_mode))
+                return (sta.st_dev == stb.st_dev) && (sta.st_ino == stb.st_ino);
+
+        /* We consider all device fds different... */
+        return false;
+}
diff --git a/src/shared/util.h b/src/shared/util.h
index a131a3c0f1..4b7e12e628 100644
--- a/src/shared/util.h
+++ b/src/shared/util.h
@@ -1069,3 +1069,5 @@ int fd_setcrtime(int fd, usec_t usec);
 int fd_getcrtime(int fd, usec_t *usec);
 int path_getcrtime(const char *p, usec_t *usec);
 int fd_getcrtime_at(int dirfd, const char *name, usec_t *usec, int flags);
+
+int same_fd(int a, int b);
diff --git a/src/systemd/sd-daemon.h b/src/systemd/sd-daemon.h
index 351b4e59c4..b878b4d8a6 100644
--- a/src/systemd/sd-daemon.h
+++ b/src/systemd/sd-daemon.h
@@ -190,6 +190,12 @@ int sd_is_mq(int fd, const char *path);
                   timestamps to detect failed services. Also see
                   sd_watchdog_enabled() below.
 
+     FDSTORE=1    Store the file descriptors passed along with the
+                  message in the per-service file descriptor store,
+                  and pass them to the main process again on next
+                  invocation. This variable is only supported with
+                  sd_pid_notify_with_fds().
+
   Daemons can choose to send additional variables. However, it is
   recommended to prefix variable names not listed above with X_.
 
@@ -243,6 +249,13 @@ int sd_pid_notify(pid_t pid, int unset_environment, const char *state);
 int sd_pid_notifyf(pid_t pid, int unset_environment, const char *format, ...) _sd_printf_(3,4);
 
 /*
+  Similar to sd_pid_notify(), but also passes the specified fd array
+  to the service manager for storage. This is particularly useful for
+  FDSTORE=1 messages.
+*/
+int sd_pid_notify_with_fds(pid_t pid, int unset_environment, const char *state, const int *fds, unsigned n_fds);
+
+/*
   Returns > 0 if the system was booted with systemd. Returns < 0 on
   error. Returns 0 if the system was not booted with systemd. Note
   that all of the functions above handle non-systemd boots just