Fix `server-name' and `server-socket-dir' for (Bug#24218)

* lisp/server.el: (server-external-socket-initialised): New
(server-name): Compute server name from `get-external-sockname'.
(server-socket-dir): Compute socket dir from
`get-external-sockname'.
(server-start): Don't check for existing server when an
uninitialised external socket has been passed to Emacs.
* src/emacs.c: (main): Obtain socket name via getsockname and pass
to `init_process_emacs'.
* src/lisp.h: (init_process_emacs): Add second parameter.
* src/process.c: (external_sock_name): New.
(get-external-sockname): New.
(init_process_emacs): Set `external_sock_name' to `sockname'
parameter.

3 files changed, 32 insertions, 5 deletions

diff --git a/src/emacs.c b/src/emacs.c
index 8ea61b71fb7..c423faf6c0d 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -60,6 +60,7 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #ifdef HAVE_LIBSYSTEMD
 # include <systemd/sd-daemon.h>
 # include <sys/socket.h>
+# include <sys/un.h>
 #endif
 
 #ifdef HAVE_WINDOW_SYSTEM
@@ -1002,6 +1003,7 @@ main (int argc, char **argv)
 
 
   int sockfd = -1;
+  char *sockname = NULL;
 
   if (argmatch (argv, argc, "-fg-daemon", "--fg-daemon", 10, NULL, &skip_args)
       || argmatch (argv, argc, "-fg-daemon", "--fg-daemon", 10, &dname_arg, &skip_args))
@@ -1061,8 +1063,16 @@ main (int argc, char **argv)
                   "Try 'Accept=false' in the Emacs socket unit file.\n"));
       else if (systemd_socket == 1
                && (0 < sd_is_socket (SD_LISTEN_FDS_START,
-                                     AF_UNSPEC, SOCK_STREAM, 1)))
-        sockfd = SD_LISTEN_FDS_START;
+                                    AF_UNIX, SOCK_STREAM, 1)))
+        {
+          struct sockaddr_un sockaddr;
+          socklen_t sockaddr_sz = sizeof(sockaddr);
+
+          sockfd = SD_LISTEN_FDS_START;
+
+          if (!getsockname(sockfd, &sockaddr, &sockaddr_sz))
+            sockname = strdup(sockaddr.sun_path);
+        }
 #endif /* HAVE_LIBSYSTEMD */
 
 #ifdef USE_GTK
@@ -1660,7 +1670,7 @@ Using an Emacs configured with --with-x-toolkit=lucid does not have this problem
   /* This can create a thread that may call getenv, so it must follow
      all calls to putenv and setenv.  Also, this sets up
      add_keyboard_wait_descriptor, which init_display uses.  */
-  init_process_emacs (sockfd);
+  init_process_emacs (sockfd, sockname);
 
   init_keyboard ();     /* This too must precede init_sys_modes.  */
   if (!noninteractive)
diff --git a/src/lisp.h b/src/lisp.h
index a7f0a1d78ff..0bd0e5e53cf 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4316,7 +4316,7 @@ extern void delete_keyboard_wait_descriptor (int);
 extern void add_gpm_wait_descriptor (int);
 extern void delete_gpm_wait_descriptor (int);
 #endif
-extern void init_process_emacs (int);
+extern void init_process_emacs (int, char *);
 extern void syms_of_process (void);
 extern void setup_process_coding_systems (Lisp_Object);
 
diff --git a/src/process.c b/src/process.c
index 2cc2c86df39..405c06db46d 100644
--- a/src/process.c
+++ b/src/process.c
@@ -276,6 +276,10 @@ static int max_desc;
    the file descriptor of a socket that is already bound.  */
 static int external_sock_fd;
 
+/* The name (path) of the socket that was passed to Emacs, when
+   `external_sock_fd' is not -1.  */
+static const char *external_sock_name = NULL;
+
 /* Indexed by descriptor, gives the process (if any) for that descriptor.  */
 static Lisp_Object chan_process[FD_SETSIZE];
 static void wait_for_socket_fds (Lisp_Object, char const *);
@@ -7972,10 +7976,21 @@ restore_nofile_limit (void)
 }
 
 
+DEFUN ("get-external-sockname", Fget_external_sockname, Sget_external_sockname, 0, 0, 0,
+       doc: /* Return the path of an external socket passed to Emacs.
+Otherwise return nil.  */)
+     (void)
+{
+    if (external_sock_name)
+        return make_string(external_sock_name, strlen(external_sock_name));
+    else
+        return Qnil;
+}
+
 /* This is not called "init_process" because that is the name of a
    Mach system call, so it would cause problems on Darwin systems.  */
 void
-init_process_emacs (int sockfd)
+init_process_emacs (int sockfd, char *sockname)
 {
 #ifdef subprocesses
   int i;
@@ -8010,6 +8025,7 @@ init_process_emacs (int sockfd)
 #endif
 
   external_sock_fd = sockfd;
+  external_sock_name = sockname;
   max_desc = -1;
   memset (fd_callback_info, 0, sizeof (fd_callback_info));
 
@@ -8304,4 +8320,5 @@ returns non-`nil'.  */);
   defsubr (&Sprocess_inherit_coding_system_flag);
   defsubr (&Slist_system_processes);
   defsubr (&Sprocess_attributes);
+  defsubr (&Sget_external_sockname);
 }