core: add support for naming file descriptors passed using socket activation

This adds support for naming file descriptors passed using socket
activation. The names are passed in a new $LISTEN_FDNAMES= environment
variable, that matches the existign $LISTEN_FDS= one and contains a
colon-separated list of names.

This also adds support for naming fds submitted to the per-service fd
store using FDNAME= in the sd_notify() message.

This also adds a new FileDescriptorName= setting for socket unit files
to set the name for fds created by socket units.

This also adds a new call sd_listen_fds_with_names(), that is similar to
sd_listen_fds(), but also returns the names of the fds.

systemd-activate gained the new --fdname= switch to specify a name for
testing socket activation.

This is based on #1247 by Maciej Wereski.

Fixes #1247.

11 files changed, 273 insertions, 97 deletions

diff --git a/src/core/dbus-socket.c b/src/core/dbus-socket.c
index 4611ad5f86..7444649f8b 100644
--- a/src/core/dbus-socket.c
+++ b/src/core/dbus-socket.c
@@ -84,6 +84,25 @@ static int property_get_listen(
         return sd_bus_message_close_container(reply);
 }
 
+
+static int property_get_fdname(
+                sd_bus *bus,
+                const char *path,
+                const char *interface,
+                const char *property,
+                sd_bus_message *reply,
+                void *userdata,
+                sd_bus_error *error) {
+
+        Socket *s = SOCKET(userdata);
+
+        assert(bus);
+        assert(reply);
+        assert(s);
+
+        return sd_bus_message_append(reply, "s", socket_fdname(s));
+}
+
 const sd_bus_vtable bus_socket_vtable[] = {
         SD_BUS_VTABLE_START(0),
         SD_BUS_PROPERTY("BindIPv6Only", "s", property_get_bind_ipv6_only, offsetof(Socket, bind_ipv6_only), SD_BUS_VTABLE_PROPERTY_CONST),
@@ -128,6 +147,7 @@ const sd_bus_vtable bus_socket_vtable[] = {
         SD_BUS_PROPERTY("Result", "s", property_get_result, offsetof(Socket, result), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("NConnections", "u", bus_property_get_unsigned, offsetof(Socket, n_connections), 0),
         SD_BUS_PROPERTY("NAccepted", "u", bus_property_get_unsigned, offsetof(Socket, n_accepted), 0),
+        SD_BUS_PROPERTY("FileDescriptorName", "s", property_get_fdname, 0, 0),
         BUS_EXEC_COMMAND_LIST_VTABLE("ExecStartPre", offsetof(Socket, exec_command[SOCKET_EXEC_START_PRE]), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
         BUS_EXEC_COMMAND_LIST_VTABLE("ExecStartPost", offsetof(Socket, exec_command[SOCKET_EXEC_START_POST]), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
         BUS_EXEC_COMMAND_LIST_VTABLE("ExecStopPre", offsetof(Socket, exec_command[SOCKET_EXEC_STOP_PRE]), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
diff --git a/src/core/execute.c b/src/core/execute.c
index 137a176c18..4664af873f 100644
--- a/src/core/execute.c
+++ b/src/core/execute.c
@@ -21,18 +21,18 @@
 
 #include <errno.h>
 #include <fcntl.h>
-#include <unistd.h>
-#include <string.h>
+#include <glob.h>
+#include <grp.h>
+#include <poll.h>
 #include <signal.h>
-#include <sys/socket.h>
-#include <sys/un.h>
+#include <string.h>
+#include <sys/personality.h>
 #include <sys/prctl.h>
+#include <sys/socket.h>
 #include <sys/stat.h>
-#include <grp.h>
-#include <poll.h>
-#include <glob.h>
+#include <sys/un.h>
+#include <unistd.h>
 #include <utmpx.h>
-#include <sys/personality.h>
 
 #ifdef HAVE_PAM
 #include <security/pam_appl.h>
@@ -50,37 +50,38 @@
 #include <sys/apparmor.h>
 #endif
 
-#include "barrier.h"
 #include "sd-messages.h"
-#include "rm-rf.h"
-#include "strv.h"
-#include "macro.h"
+
+#include "af-list.h"
+#include "async.h"
+#include "barrier.h"
+#include "bus-endpoint.h"
+#include "cap-list.h"
 #include "capability.h"
-#include "util.h"
-#include "log.h"
-#include "ioprio.h"
-#include "securebits.h"
-#include "namespace.h"
-#include "exit-status.h"
-#include "missing.h"
-#include "utmp-wtmp.h"
 #include "def.h"
-#include "path-util.h"
 #include "env-util.h"
-#include "fileio.h"
-#include "unit.h"
-#include "async.h"
-#include "selinux-util.h"
 #include "errno-list.h"
-#include "af-list.h"
-#include "mkdir.h"
-#include "smack-util.h"
-#include "bus-endpoint.h"
-#include "cap-list.h"
+#include "exit-status.h"
+#include "fileio.h"
 #include "formats-util.h"
+#include "ioprio.h"
+#include "log.h"
+#include "macro.h"
+#include "missing.h"
+#include "mkdir.h"
+#include "namespace.h"
+#include "path-util.h"
 #include "process-util.h"
-#include "terminal-util.h"
+#include "rm-rf.h"
+#include "securebits.h"
+#include "selinux-util.h"
 #include "signal-util.h"
+#include "smack-util.h"
+#include "strv.h"
+#include "terminal-util.h"
+#include "unit.h"
+#include "util.h"
+#include "utmp-wtmp.h"
 
 #ifdef HAVE_APPARMOR
 #include "apparmor-util.h"
@@ -1198,6 +1199,7 @@ static void do_idle_pipe_dance(int idle_pipe[4]) {
 static int build_environment(
                 const ExecContext *c,
                 unsigned n_fds,
+                char ** fd_names,
                 usec_t watchdog_usec,
                 const char *home,
                 const char *username,
@@ -1211,11 +1213,13 @@ static int build_environment(
         assert(c);
         assert(ret);
 
-        our_env = new0(char*, 10);
+        our_env = new0(char*, 11);
         if (!our_env)
                 return -ENOMEM;
 
         if (n_fds > 0) {
+                _cleanup_free_ char *joined = NULL;
+
                 if (asprintf(&x, "LISTEN_PID="PID_FMT, getpid()) < 0)
                         return -ENOMEM;
                 our_env[n_env++] = x;
@@ -1223,6 +1227,15 @@ static int build_environment(
                 if (asprintf(&x, "LISTEN_FDS=%u", n_fds) < 0)
                         return -ENOMEM;
                 our_env[n_env++] = x;
+
+                joined = strv_join(fd_names, ":");
+                if (!joined)
+                        return -ENOMEM;
+
+                x = strjoin("LISTEN_FDNAMES=", joined, NULL);
+                if (!x)
+                        return -ENOMEM;
+                our_env[n_env++] = x;
         }
 
         if (watchdog_usec > 0) {
@@ -1273,7 +1286,7 @@ static int build_environment(
         }
 
         our_env[n_env++] = NULL;
-        assert(n_env <= 10);
+        assert(n_env <= 11);
 
         *ret = our_env;
         our_env = NULL;
@@ -1850,7 +1863,7 @@ static int exec_child(
 #endif
         }
 
-        r = build_environment(context, n_fds, params->watchdog_usec, home, username, shell, &our_env);
+        r = build_environment(context, n_fds, params->fd_names, params->watchdog_usec, home, username, shell, &our_env);
         if (r < 0) {
                 *exit_status = EXIT_MEMORY;
                 return r;
diff --git a/src/core/execute.h b/src/core/execute.h
index 2c93044748..f1c37116fd 100644
--- a/src/core/execute.h
+++ b/src/core/execute.h
@@ -208,19 +208,30 @@ struct ExecContext {
 
 struct ExecParameters {
         char **argv;
-        int *fds; unsigned n_fds;
+
+        int *fds;
+        char **fd_names;
+        unsigned n_fds;
+
         char **environment;
+
         bool apply_permissions;
         bool apply_chroot;
         bool apply_tty_stdin;
+
         bool confirm_spawn;
         bool selinux_context_net;
+
         CGroupMask cgroup_supported;
         const char *cgroup_path;
         bool cgroup_delegate;
+
         const char *runtime_prefix;
+
         usec_t watchdog_usec;
+
         int *idle_pipe;
+
         char *bus_endpoint_path;
         int bus_endpoint_fd;
 };
diff --git a/src/core/load-fragment-gperf.gperf.m4 b/src/core/load-fragment-gperf.gperf.m4
index 2333926e7d..89e624b557 100644
--- a/src/core/load-fragment-gperf.gperf.m4
+++ b/src/core/load-fragment-gperf.gperf.m4
@@ -287,6 +287,7 @@ Socket.MessageQueueMaxMessages,  config_parse_long,                  0,
 Socket.MessageQueueMessageSize,  config_parse_long,                  0,                             offsetof(Socket, mq_msgsize)
 Socket.RemoveOnStop,             config_parse_bool,                  0,                             offsetof(Socket, remove_on_stop)
 Socket.Symlinks,                 config_parse_unit_path_strv_printf, 0,                             offsetof(Socket, symlinks)
+Socket.FileDescriptorName,       config_parse_fdname,                0,                             0
 Socket.Service,                  config_parse_socket_service,        0,                             0
 m4_ifdef(`HAVE_SMACK',
 `Socket.SmackLabel,              config_parse_string,                0,                             offsetof(Socket, smack)
diff --git a/src/core/load-fragment.c b/src/core/load-fragment.c
index fc2755cb92..b1d4c6b57d 100644
--- a/src/core/load-fragment.c
+++ b/src/core/load-fragment.c
@@ -1475,10 +1475,10 @@ int config_parse_socket_service(
                 void *userdata) {
 
         _cleanup_bus_error_free_ sd_bus_error error = SD_BUS_ERROR_NULL;
+        _cleanup_free_ char *p = NULL;
         Socket *s = data;
-        int r;
         Unit *x;
-        _cleanup_free_ char *p = NULL;
+        int r;
 
         assert(filename);
         assert(lvalue);
@@ -1507,6 +1507,50 @@ int config_parse_socket_service(
         return 0;
 }
 
+int config_parse_fdname(
+                const char *unit,
+                const char *filename,
+                unsigned line,
+                const char *section,
+                unsigned section_line,
+                const char *lvalue,
+                int ltype,
+                const char *rvalue,
+                void *data,
+                void *userdata) {
+
+        _cleanup_free_ char *p = NULL;
+        Socket *s = data;
+        int r;
+
+        assert(filename);
+        assert(lvalue);
+        assert(rvalue);
+        assert(data);
+
+        if (isempty(rvalue)) {
+                s->fdname = mfree(s->fdname);
+                return 0;
+        }
+
+        r = unit_name_printf(UNIT(s), rvalue, &p);
+        if (r < 0) {
+                log_syntax(unit, LOG_ERR, filename, line, r, "Failed to resolve specifiers, ignoring: %s", rvalue);
+                return 0;
+        }
+
+        if (!fdname_is_valid(p)) {
+                log_syntax(unit, LOG_ERR, filename, line, 0, "Invalid file descriptor name, ignoring: %s", p);
+                return 0;
+        }
+
+        free(s->fdname);
+        s->fdname = p;
+        p = NULL;
+
+        return 0;
+}
+
 int config_parse_service_sockets(
                 const char *unit,
                 const char *filename,
diff --git a/src/core/load-fragment.h b/src/core/load-fragment.h
index 6ee7c71bc4..8661cbfedc 100644
--- a/src/core/load-fragment.h
+++ b/src/core/load-fragment.h
@@ -107,6 +107,7 @@ int config_parse_protect_system(const char* unit, const char *filename, unsigned
 int config_parse_bus_name(const char* unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_exec_utmp_mode(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_working_directory(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
+int config_parse_fdname(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 
 /* gperf prototypes */
 const struct ConfigPerfItem* load_fragment_gperf_lookup(const char *key, unsigned length);
diff --git a/src/core/manager.c b/src/core/manager.c
index 9de9691a47..526d4d1cef 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -495,6 +495,7 @@ static void manager_clean_environment(Manager *m) {
                         "MANAGERPID",
                         "LISTEN_PID",
                         "LISTEN_FDS",
+                        "LISTEN_FDNAMES",
                         "WATCHDOG_PID",
                         "WATCHDOG_USEC",
                         NULL);
diff --git a/src/core/service.c b/src/core/service.c
index 2c78cb96c2..c941689dd7 100644
--- a/src/core/service.c
+++ b/src/core/service.c
@@ -261,6 +261,7 @@ static void service_fd_store_unlink(ServiceFDStore *fs) {
                 sd_event_source_unref(fs->event_source);
         }
 
+        free(fs->fdname);
         safe_close(fs->fd);
         free(fs);
 }
@@ -334,7 +335,7 @@ static int on_fd_store_io(sd_event_source *e, int fd, uint32_t revents, void *us
         return 0;
 }
 
-static int service_add_fd_store(Service *s, int fd) {
+static int service_add_fd_store(Service *s, int fd, const char *name) {
         ServiceFDStore *fs;
         int r;
 
@@ -361,9 +362,13 @@ static int service_add_fd_store(Service *s, int fd) {
 
         fs->fd = fd;
         fs->service = s;
+        fs->fdname = strdup(name ?: "stored");
+        if (!fs->fdname)
+                return -ENOMEM;
 
         r = sd_event_add_io(UNIT(s)->manager->event, &fs->event_source, fd, 0, on_fd_store_io, fs);
         if (r < 0) {
+                free(fs->fdname);
                 free(fs);
                 return r;
         }
@@ -376,7 +381,7 @@ static int service_add_fd_store(Service *s, int fd) {
         return 1;
 }
 
-static int service_add_fd_store_set(Service *s, FDSet *fds) {
+static int service_add_fd_store_set(Service *s, FDSet *fds, const char *name) {
         int r;
 
         assert(s);
@@ -391,7 +396,7 @@ static int service_add_fd_store_set(Service *s, FDSet *fds) {
                 if (fd < 0)
                         break;
 
-                r = service_add_fd_store(s, fd);
+                r = service_add_fd_store(s, fd, name);
                 if (r < 0)
                         return log_unit_error_errno(UNIT(s), r, "Couldn't add fd to fd store: %m");
                 if (r > 0) {
@@ -957,56 +962,79 @@ static int service_coldplug(Unit *u) {
         return 0;
 }
 
-static int service_collect_fds(Service *s, int **fds) {
+static int service_collect_fds(Service *s, int **fds, char ***fd_names) {
+        _cleanup_strv_free_ char **rfd_names = NULL;
         _cleanup_free_ int *rfds = NULL;
-        int rn_fds = 0;
-        Iterator i;
-        Unit *u;
+        int rn_fds = 0, r;
 
         assert(s);
         assert(fds);
+        assert(fd_names);
 
-        if (s->socket_fd >= 0)
-                return -EINVAL;
+        if (s->socket_fd >= 0) {
 
-        SET_FOREACH(u, UNIT(s)->dependencies[UNIT_TRIGGERED_BY], i) {
-                _cleanup_free_ int *cfds = NULL;
-                Socket *sock;
-                int cn_fds;
+                /* Pass the per-connection socket */
 
-                if (u->type != UNIT_SOCKET)
-                        continue;
+                rfds = new(int, 1);
+                if (!rfds)
+                        return -ENOMEM;
+                rfds[0] = s->socket_fd;
+
+                rfd_names = strv_new("connection", NULL);
+                if (!rfd_names)
+                        return -ENOMEM;
 
-                sock = SOCKET(u);
+                rn_fds = 1;
+        } else {
+                Iterator i;
+                Unit *u;
 
-                cn_fds = socket_collect_fds(sock, &cfds);
-                if (cn_fds < 0)
-                        return cn_fds;
+                /* Pass all our configured sockets for singleton services */
 
-                if (cn_fds <= 0)
-                        continue;
+                SET_FOREACH(u, UNIT(s)->dependencies[UNIT_TRIGGERED_BY], i) {
+                        _cleanup_free_ int *cfds = NULL;
+                        Socket *sock;
+                        int cn_fds;
 
-                if (!rfds) {
-                        rfds = cfds;
-                        rn_fds = cn_fds;
+                        if (u->type != UNIT_SOCKET)
+                                continue;
 
-                        cfds = NULL;
-                } else {
-                        int *t;
+                        sock = SOCKET(u);
 
-                        t = realloc(rfds, (rn_fds + cn_fds) * sizeof(int));
-                        if (!t)
-                                return -ENOMEM;
+                        cn_fds = socket_collect_fds(sock, &cfds);
+                        if (cn_fds < 0)
+                                return cn_fds;
+
+                        if (cn_fds <= 0)
+                                continue;
+
+                        if (!rfds) {
+                                rfds = cfds;
+                                rn_fds = cn_fds;
 
-                        memcpy(t + rn_fds, cfds, cn_fds * sizeof(int));
+                                cfds = NULL;
+                        } else {
+                                int *t;
 
-                        rfds = t;
-                        rn_fds += cn_fds;
+                                t = realloc(rfds, (rn_fds + cn_fds) * sizeof(int));
+                                if (!t)
+                                        return -ENOMEM;
+
+                                memcpy(t + rn_fds, cfds, cn_fds * sizeof(int));
+
+                                rfds = t;
+                                rn_fds += cn_fds;
+                        }
+
+                        r = strv_extend_n(&rfd_names, socket_fdname(sock), cn_fds);
+                        if (r < 0)
+                                return r;
                 }
         }
 
         if (s->n_fd_store > 0) {
                 ServiceFDStore *fs;
+                char **nl;
                 int *t;
 
                 t = realloc(rfds, (rn_fds + s->n_fd_store) * sizeof(int));
@@ -1014,12 +1042,30 @@ static int service_collect_fds(Service *s, int **fds) {
                         return -ENOMEM;
 
                 rfds = t;
-                LIST_FOREACH(fd_store, fs, s->fd_store)
-                        rfds[rn_fds++] = fs->fd;
+
+                nl = realloc(rfd_names, (rn_fds + s->n_fd_store + 1) * sizeof(char*));
+                if (!nl)
+                        return -ENOMEM;
+
+                rfd_names = nl;
+
+                LIST_FOREACH(fd_store, fs, s->fd_store) {
+                        rfds[rn_fds] = fs->fd;
+                        rfd_names[rn_fds] = strdup(strempty(fs->fdname));
+                        if (!rfd_names[rn_fds])
+                                return -ENOMEM;
+
+                        rn_fds++;
+                }
+
+                rfd_names[rn_fds] = NULL;
         }
 
         *fds = rfds;
+        *fd_names = rfd_names;
+
         rfds = NULL;
+        rfd_names = NULL;
 
         return rn_fds;
 }
@@ -1035,15 +1081,13 @@ static int service_spawn(
                 bool is_control,
                 pid_t *_pid) {
 
-        pid_t pid;
-        int r;
-        int *fds = NULL;
-        _cleanup_free_ int *fdsbuf = NULL;
-        unsigned n_fds = 0, n_env = 0;
+        _cleanup_strv_free_ char **argv = NULL, **final_env = NULL, **our_env = NULL, **fd_names = NULL;
         _cleanup_free_ char *bus_endpoint_path = NULL;
-        _cleanup_strv_free_ char
-                **argv = NULL, **final_env = NULL, **our_env = NULL;
+        _cleanup_free_ int *fds = NULL;
+        unsigned n_fds = 0, n_env = 0;
         const char *path;
+        pid_t pid;
+
         ExecParameters exec_params = {
                 .apply_permissions   = apply_permissions,
                 .apply_chroot        = apply_chroot,
@@ -1052,6 +1096,8 @@ static int service_spawn(
                 .selinux_context_net = s->socket_fd_selinux_context_net
         };
 
+        int r;
+
         assert(s);
         assert(c);
         assert(_pid);
@@ -1071,17 +1117,11 @@ static int service_spawn(
             s->exec_context.std_output == EXEC_OUTPUT_SOCKET ||
             s->exec_context.std_error == EXEC_OUTPUT_SOCKET) {
 
-                if (s->socket_fd >= 0) {
-                        fds = &s->socket_fd;
-                        n_fds = 1;
-                } else {
-                        r = service_collect_fds(s, &fdsbuf);
-                        if (r < 0)
-                                goto fail;
+                r = service_collect_fds(s, &fds, &fd_names);
+                if (r < 0)
+                        goto fail;
 
-                        fds = fdsbuf;
-                        n_fds = r;
-                }
+                n_fds = r;
         }
 
         if (timeout > 0) {
@@ -1119,7 +1159,7 @@ static int service_spawn(
                         goto fail;
                 }
 
-        if (UNIT_DEREF(s->accept_socket)) {
+        if (s->socket_fd >= 0) {
                 union sockaddr_union sa;
                 socklen_t salen = sizeof(sa);
 
@@ -1185,6 +1225,7 @@ static int service_spawn(
 
         exec_params.argv = argv;
         exec_params.fds = fds;
+        exec_params.fd_names = fd_names;
         exec_params.n_fds = n_fds;
         exec_params.environment = final_env;
         exec_params.confirm_spawn = UNIT(s)->manager->confirm_spawn;
@@ -2047,13 +2088,16 @@ static int service_serialize(Unit *u, FILE *f, FDSet *fds) {
         }
 
         LIST_FOREACH(fd_store, fs, s->fd_store) {
+                _cleanup_free_ char *c = NULL;
                 int copy;
 
                 copy = fdset_put_dup(fds, fs->fd);
                 if (copy < 0)
                         return copy;
 
-                unit_serialize_item_format(u, f, "fd-store-fd", "%i", copy);
+                c = cescape(fs->fdname);
+
+                unit_serialize_item_format(u, f, "fd-store-fd", "%i %s", copy, strempty(c));
         }
 
         if (s->main_exec_status.pid > 0) {
@@ -2183,12 +2227,24 @@ static int service_deserialize_item(Unit *u, const char *key, const char *value,
                         s->bus_endpoint_fd = fdset_remove(fds, fd);
                 }
         } else if (streq(key, "fd-store-fd")) {
+                const char *fdv;
+                size_t pf;
                 int fd;
 
-                if (safe_atoi(value, &fd) < 0 || fd < 0 || !fdset_contains(fds, fd))
+                pf = strcspn(value, WHITESPACE);
+                fdv = strndupa(value, pf);
+
+                if (safe_atoi(fdv, &fd) < 0 || fd < 0 || !fdset_contains(fds, fd))
                         log_unit_debug(u, "Failed to parse fd-store-fd value: %s", value);
                 else {
-                        r = service_add_fd_store(s, fd);
+                        _cleanup_free_ char *t = NULL;
+                        const char *fdn;
+
+                        fdn = value + pf;
+                        fdn += strspn(fdn, WHITESPACE);
+                        (void) cunescape(fdn, 0, &t);
+
+                        r = service_add_fd_store(s, fd, t);
                         if (r < 0)
                                 log_unit_error_errno(u, r, "Failed to add fd to store: %m");
                         else if (r > 0)
@@ -2942,8 +2998,17 @@ static void service_notify_message(Unit *u, pid_t pid, char **tags, FDSet *fds)
         if (strv_find(tags, "WATCHDOG=1"))
                 service_reset_watchdog(s);
 
-        if (strv_find(tags, "FDSTORE=1"))
-                service_add_fd_store_set(s, fds);
+        if (strv_find(tags, "FDSTORE=1")) {
+                const char *name;
+
+                name = strv_find_startswith(tags, "FDNAME=");
+                if (name && !fdname_is_valid(name)) {
+                        log_unit_warning(u, "Passed FDNAME= name is invalid, ignoring.");
+                        name = NULL;
+                }
+
+                service_add_fd_store_set(s, fds, name);
+        }
 
         /* Notify clients about changed status or main pid */
         if (notify_dbus)
diff --git a/src/core/service.h b/src/core/service.h
index a8d42706bd..61bb44fbcf 100644
--- a/src/core/service.h
+++ b/src/core/service.h
@@ -97,6 +97,7 @@ struct ServiceFDStore {
         Service *service;
 
         int fd;
+        char *fdname;
         sd_event_source *event_source;
 
         LIST_FIELDS(ServiceFDStore, fd_store);
diff --git a/src/core/socket.c b/src/core/socket.c
index 4462fbd72d..6300b20f3e 100644
--- a/src/core/socket.c
+++ b/src/core/socket.c
@@ -508,6 +508,7 @@ static void socket_dump(Unit *u, FILE *f, const char *prefix) {
                 "%sTCPCongestion: %s\n"
                 "%sRemoveOnStop: %s\n"
                 "%sWritable: %s\n"
+                "%sFDName: %s\n"
                 "%sSELinuxContextFromNet: %s\n",
                 prefix, socket_state_to_string(s->state),
                 prefix, socket_result_to_string(s->result),
@@ -525,6 +526,7 @@ static void socket_dump(Unit *u, FILE *f, const char *prefix) {
                 prefix, strna(s->tcp_congestion),
                 prefix, yes_no(s->remove_on_stop),
                 prefix, yes_no(s->writable),
+                prefix, socket_fdname(s),
                 prefix, yes_no(s->selinux_context_from_net));
 
         if (s->control_pid > 0)
@@ -2760,6 +2762,19 @@ static int socket_get_timeout(Unit *u, uint64_t *timeout) {
         return 1;
 }
 
+char *socket_fdname(Socket *s) {
+        assert(s);
+
+        /* Returns the name to use for $LISTEN_NAMES. If the user
+         * didn't specify anything specifically, use the socket unit's
+         * name as fallback. */
+
+        if (s->fdname)
+                return s->fdname;
+
+        return UNIT(s)->id;
+}
+
 static const char* const socket_exec_command_table[_SOCKET_EXEC_COMMAND_MAX] = {
         [SOCKET_EXEC_START_PRE] = "StartPre",
         [SOCKET_EXEC_START_CHOWN] = "StartChown",
diff --git a/src/core/socket.h b/src/core/socket.h
index 96091b0609..94cda8a90d 100644
--- a/src/core/socket.h
+++ b/src/core/socket.h
@@ -154,6 +154,8 @@ struct Socket {
         char *user, *group;
 
         bool reset_cpu_usage:1;
+
+        char *fdname;
 };
 
 /* Called from the service code when collecting fds */
@@ -164,6 +166,10 @@ void socket_connection_unref(Socket *s);
 
 void socket_free_ports(Socket *s);
 
+int socket_instantiate_service(Socket *s);
+
+char *socket_fdname(Socket *s);
+
 extern const UnitVTable socket_vtable;
 
 const char* socket_exec_command_to_string(SocketExecCommand i) _const_;
@@ -173,5 +179,3 @@ const char* socket_result_to_string(SocketResult i) _const_;
 SocketResult socket_result_from_string(const char *s) _pure_;
 
 const char* socket_port_type_to_string(SocketPort *p) _pure_;
-
-int socket_instantiate_service(Socket *s);