[PATCH v2 0/4] Add systemd socket launching support.

[PATCH v2 0/4] Add systemd socket launching support.

[Matthew Leach]

Hi all,

systemd has the ability to create a socket, launch a daemon upon
connection to that socket and hand over the socket to the new process
to handle.  In Emacs' case, we can delay the start of the Emacs daemon
until emacsclient is called upon a socket.

These patches can be tested by creating minimal systemd setup.  First,
create two systemd unit files:

emacs.socket
============
[Socket]
ListenStream=/home/foobar/test.socket

[Install]
WantedBy=sockets.target

emacs.service
=============
[Service]
Type=forking
ExecStart=/path/to/emacs --daemon

Once these files have been created, execute:

# systemctl daemon-reload
# systemctl start enacs.socket

The socket will now be created, and when a connection is made, the
Emacs daemon will be started:

# emacsclient -s /home/foobar/test.socket -t

Feedback & comments welcome!

Thanks,
Matt

Changes since v1
================
* Call sd_listen_fds with a paramter of 1 to remove the state that
  systemd sets up.
* Check the socket's validity when passed from systemd.
* Remove lisp functions to simplify the API.
* Change the name of the paramter passed to make_network_process to
  ':usepassedsocket' to keep things more generic.

Matthew Leach (4):
  Check for libsystemd when building Emacs.
  Read the number of sockets passed by systemd.
  Allow network processes to be made with a pre-allocated fd.
  When Emacs is passed a socket descriptor, make the server listen on
    it.

 configure.ac    | 13 +++++++++++++
 lisp/server.el  |  1 +
 src/Makefile.in |  6 +++++-
 src/emacs.c     | 25 +++++++++++++++++++++++++
 src/process.c   | 36 +++++++++++++++++++++++++++++-------
 5 files changed, 73 insertions(+), 8 deletions(-)

-- 
2.7.4

[PATCH v2 1/4] Check for libsystemd when building Emacs.

[Matthew Leach]

* configure.ac: Add new default-on option systemd and check for
  necessary systemd libraries at configure time.
* src/Makefile.in: Add libsystemd library and C flags to the Emacs
  compilation options.
---
 configure.ac    | 13 +++++++++++++
 src/Makefile.in |  6 +++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index f3846f4..d3628d2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -330,6 +330,7 @@ OPTION_DEFAULT_ON([tiff],[don't compile with TIFF image support])
 OPTION_DEFAULT_ON([gif],[don't compile with GIF image support])
 OPTION_DEFAULT_ON([png],[don't compile with PNG image support])
 OPTION_DEFAULT_ON([rsvg],[don't compile with SVG image support])
+OPTION_DEFAULT_ON([systemd],[don't compile with systemd support])
 OPTION_DEFAULT_OFF([cairo],[compile with Cairo drawing (experimental)])
 OPTION_DEFAULT_ON([xml2],[don't compile with XML parsing support])
 OPTION_DEFAULT_ON([imagemagick],[don't compile with ImageMagick image support])
@@ -2716,6 +2717,18 @@ fi
 AC_SUBST(LIBGNUTLS_LIBS)
 AC_SUBST(LIBGNUTLS_CFLAGS)
 
+HAVE_SYSTEMD=no
+if test "${with_systemd}" = "yes" ; then
+  EMACS_CHECK_MODULES([LIBSYSTEMD], [libsystemd >= 226],
+    [HAVE_SYSTEMD=yes], [HAVE_SYSTEMD=no])
+  if test "${HAVE_SYSTEMD}" = "yes"; then
+    AC_DEFINE(HAVE_SYSTEMD, 1, [Define if using systemd.])
+  fi
+fi
+
+AC_SUBST(LIBSYSTEMD_LIBS)
+AC_SUBST(LIBSYSTEMD_CFLAGS)
+
 NOTIFY_OBJ=
 NOTIFY_SUMMARY=no
 
diff --git a/src/Makefile.in b/src/Makefile.in
index c290a60..fc9360a 100644
--- a/src/Makefile.in
+++ b/src/Makefile.in
@@ -307,6 +307,9 @@ LIBSELINUX_LIBS = @LIBSELINUX_LIBS@
 LIBGNUTLS_LIBS = @LIBGNUTLS_LIBS@
 LIBGNUTLS_CFLAGS = @LIBGNUTLS_CFLAGS@
 
+LIBSYSTEMD_LIBS = @LIBSYSTEMD_LIBS@
+LIBSYSTEMD_CFLAGS = @LIBSYSTEMD_CFLAGS@
+
 INTERVALS_H = dispextern.h intervals.h composite.h
 
 GETLOADAVG_LIBS = @GETLOADAVG_LIBS@
@@ -372,6 +375,7 @@ ALL_CFLAGS=-Demacs $(MYCPPFLAGS) -I. -I$(srcdir) \
   $(WEBKIT_CFLAGS) \
   $(SETTINGS_CFLAGS) $(FREETYPE_CFLAGS) $(FONTCONFIG_CFLAGS) \
   $(LIBOTF_CFLAGS) $(M17N_FLT_CFLAGS) $(DEPFLAGS) \
+  $(LIBSYSTEMD_CFLAGS) \
   $(LIBGNUTLS_CFLAGS) $(NOTIFY_CFLAGS) $(CAIRO_CFLAGS) \
   $(WARN_CFLAGS) $(WERROR_CFLAGS) $(CFLAGS)
 ALL_OBJC_CFLAGS=$(ALL_CFLAGS) $(GNU_OBJC_CFLAGS)
@@ -489,7 +493,7 @@ LIBES = $(LIBS) $(W32_LIBS) $(LIBS_GNUSTEP) $(LIBX_BASE) $(LIBIMAGE) \
    $(LIBS_TERMCAP) $(GETLOADAVG_LIBS) $(SETTINGS_LIBS) $(LIBSELINUX_LIBS) \
    $(FREETYPE_LIBS) $(FONTCONFIG_LIBS) $(LIBOTF_LIBS) $(M17N_FLT_LIBS) \
    $(LIBGNUTLS_LIBS) $(LIB_PTHREAD) $(GETADDRINFO_A_LIBS) \
-   $(NOTIFY_LIBS) $(LIB_MATH) $(LIBZ) $(LIBMODULES)
+   $(NOTIFY_LIBS) $(LIB_MATH) $(LIBZ) $(LIBMODULES) $(LIBSYSTEMD_LIBS)
 
 $(leimdir)/leim-list.el: bootstrap-emacs$(EXEEXT)
 	$(MAKE) -C ../leim leim-list.el EMACS="$(bootstrap_exe)"
-- 
2.7.4

[PATCH v2 2/4] Read the number of sockets passed by systemd.

[Matthew Leach]

* src/emacs.c (systemd_socket): New variable for storing the socket
  descriptor passed in by systemd.
  (main): Call sd_listen_fds to read the number of sockets passed.
---
 src/emacs.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/src/emacs.c b/src/emacs.c
index 95d1905..df5fade 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -56,6 +56,11 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <binary-io.h>
 #endif
 
+#ifdef HAVE_SYSTEMD
+#include <systemd/sd-daemon.h>
+#include <sys/socket.h>
+#endif /* HAVE_SYSTEMD */
+
 #ifdef HAVE_WINDOW_SYSTEM
 #include TERM_HEADER
 #endif /* HAVE_WINDOW_SYSTEM */
@@ -195,6 +200,12 @@ int daemon_pipe[2];
 HANDLE w32_daemon_event;
 #endif
 
+#ifdef HAVE_SYSTEMD
+/* The socket descriptor passed by systemd.  If nothing has been
+   passed, this will be 0. */
+int systemd_socket = 0;
+#endif /* HAVE_SYSTEMD */
+
 /* Save argv and argc.  */
 char **initial_argv;
 int initial_argc;
@@ -997,6 +1008,24 @@ main (int argc, char **argv)
 	  exit (1);
 	}
 
+#ifdef HAVE_SYSTEMD
+      /* Read the number of sockets passed through by systemd. */
+      systemd_socket = sd_listen_fds(1);
+
+      if (systemd_socket > 1)
+        {
+          fprintf (stderr, "\nWarning: systemd has passed more than one socket to the Emacs process.\n\
+Try adding 'Accept=false' in the Emacs socket unit file.\n");
+          systemd_socket = 0;
+        }
+      else if (systemd_socket == 1 &&
+               sd_is_socket (SD_LISTEN_FDS_START,
+                             AF_UNSPEC, SOCK_STREAM, 1) >= 0)
+        systemd_socket = SD_LISTEN_FDS_START;
+      else
+        systemd_socket = 0;
+#endif
+
 #ifndef DAEMON_MUST_EXEC
 #ifdef USE_GTK
       fprintf (stderr, "\nWarning: due to a long standing Gtk+ bug\nhttp://bugzilla.gnome.org/show_bug.cgi?id=85715\n\
-- 
2.7.4

[PATCH v2 3/4] Allow network processes to be made with a pre-allocated fd.

[Matthew Leach]

* src/process.c (connect_network_socket): Allow a pre-allocated
socket descriptor to be used if passed to Emacs, avoiding the call
to socket() and bind().
(Fmake_network_process): Allow users to pass in :usepassedsocket
on the parameter plist to use a socket descriptor that has been
passed to Emacs.
(wait_reading_process_output): Call socket() & bind() every time.
(syms_of_process): New symbol ":usepassedsocket".
---
 src/process.c | 36 +++++++++++++++++++++++++++++-------
 1 file changed, 29 insertions(+), 7 deletions(-)

diff --git a/src/process.c b/src/process.c
index 198e7de..2a0a0d5 100644
--- a/src/process.c
+++ b/src/process.c
@@ -3075,7 +3075,8 @@ finish_after_tls_connection (Lisp_Object proc)
 #endif
 
 static void
-connect_network_socket (Lisp_Object proc, Lisp_Object ip_addresses)
+connect_network_socket (Lisp_Object proc, Lisp_Object ip_addresses,
+                        Lisp_Object use_passed_socket_p)
 {
   ptrdiff_t count = SPECPDL_INDEX ();
   ptrdiff_t count1;
@@ -3089,6 +3090,16 @@ connect_network_socket (Lisp_Object proc, Lisp_Object ip_addresses)
   struct Lisp_Process *p = XPROCESS (proc);
   Lisp_Object contact = p->childp;
   int optbits = 0;
+  int passed_socket_descriptor = 0;
+
+#ifdef HAVE_SYSTEMD
+  if (!NILP (use_passed_socket_p))
+    {
+      extern int systemd_socket;
+      passed_socket_descriptor = systemd_socket;
+    }
+#endif /* HAVE_SYSTEMD */
+
 
   /* Do this in case we never enter the while-loop below.  */
   count1 = SPECPDL_INDEX ();
@@ -3109,7 +3120,11 @@ connect_network_socket (Lisp_Object proc, Lisp_Object ip_addresses)
       sa = xmalloc (addrlen);
       conv_lisp_to_sockaddr (family, ip_address, sa, addrlen);
 
-      s = socket (family, p->socktype | SOCK_CLOEXEC, p->ai_protocol);
+      if (passed_socket_descriptor)
+          s = passed_socket_descriptor;
+      else
+          s = socket (family, p->socktype | SOCK_CLOEXEC, p->ai_protocol);
+
       if (s < 0)
 	{
 	  xerrno = errno;
@@ -3168,8 +3183,11 @@ connect_network_socket (Lisp_Object proc, Lisp_Object ip_addresses)
 		  report_file_error ("Cannot set reuse option on server socket", Qnil);
 	      }
 
-	  if (bind (s, sa, addrlen))
-	    report_file_error ("Cannot bind server socket", Qnil);
+          /* If we are passed a socket descriptor, it is already
+             bound. */
+	  if (!passed_socket_descriptor)
+	    if (bind (s, sa, addrlen))
+	      report_file_error ("Cannot bind server socket", Qnil);
 
 #ifdef HAVE_GETSOCKNAME
 	  if (p->port == 0)
@@ -3534,6 +3552,8 @@ The following network options can be specified for this connection:
                       (this is allowed by default for a server process).
 :bindtodevice NAME -- bind to interface NAME.  Using this may require
                       special privileges on some systems.
+:usepassedsocket BOOL -- Use any pre-allocated sockets that have
+                         been passed to Emacs.
 
 Consult the relevant system programmer's manual pages for more
 information on using these options.
@@ -3578,7 +3598,7 @@ usage: (make-network-process &rest ARGS)  */)
   EMACS_INT port = 0;
   Lisp_Object tem;
   Lisp_Object name, buffer, host, service, address;
-  Lisp_Object filter, sentinel;
+  Lisp_Object filter, sentinel, use_passed_socket_p;
   Lisp_Object ip_addresses = Qnil;
   int socktype;
   int family = -1;
@@ -3618,6 +3638,7 @@ usage: (make-network-process &rest ARGS)  */)
   buffer = Fplist_get (contact, QCbuffer);
   filter = Fplist_get (contact, QCfilter);
   sentinel = Fplist_get (contact, QCsentinel);
+  use_passed_socket_p = Fplist_get (contact, QCuse_passed_socket);
 
   CHECK_STRING (name);
 
@@ -3914,7 +3935,7 @@ usage: (make-network-process &rest ARGS)  */)
     }
 #endif
 
-  connect_network_socket (proc, ip_addresses);
+  connect_network_socket (proc, ip_addresses, use_passed_socket_p);
   return proc;
 }
 
@@ -4848,7 +4869,7 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
 		  {
 		    Lisp_Object ip_addresses = check_for_dns (aproc);
 		    if (!NILP (ip_addresses) && !EQ (ip_addresses, Qt))
-		      connect_network_socket (aproc, ip_addresses);
+		      connect_network_socket (aproc, ip_addresses, Qnil);
 		    else
 		      retry_for_async = true;
 		  }
@@ -7837,6 +7858,7 @@ syms_of_process (void)
   DEFSYM (QCserver, ":server");
   DEFSYM (QCnowait, ":nowait");
   DEFSYM (QCsentinel, ":sentinel");
+  DEFSYM (QCuse_passed_socket, ":usepassedsocket");
   DEFSYM (QCtls_parameters, ":tls-parameters");
   DEFSYM (Qnsm_verify_connection, "nsm-verify-connection");
   DEFSYM (QClog, ":log");
-- 
2.7.4

[PATCH v2 4/4] When Emacs is passed a socket descriptor, make the server listen on it.

[Matthew Leach]

* lisp/server.el (server-start): Set :usepassedsocket to `t' when
  calling `make-network-process'.
---
 lisp/server.el | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lisp/server.el b/lisp/server.el
index 5243820..9c04262 100644
--- a/lisp/server.el
+++ b/lisp/server.el
@@ -655,6 +655,7 @@ server or call `\\[server-force-delete]' to forcibly disconnect it."))
 		       :noquery t
 		       :sentinel #'server-sentinel
 		       :filter #'server-process-filter
+		       :usepassedsocket t
 		       ;; We must receive file names without being decoded.
 		       ;; Those are decoded by server-process-filter according
 		       ;; to file-name-coding-system.  Also don't get
-- 
2.7.4

Re: [PATCH v2 3/4] Allow network processes to be made with a pre-allocated fd.

[Andreas Schwab]

Matthew Leach <matthew@mattleach.net> writes:

> @@ -7837,6 +7858,7 @@ syms_of_process (void)
>    DEFSYM (QCserver, ":server");
>    DEFSYM (QCnowait, ":nowait");
>    DEFSYM (QCsentinel, ":sentinel");
> +  DEFSYM (QCuse_passed_socket, ":usepassedsocket");

Please use the same spelling for the variable and the symbol.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: [PATCH v2 3/4] Allow network processes to be made with a pre-allocated fd.

[Eli Zaretskii]

> From: Matthew Leach <matthew@mattleach.net>
> Date: Sun, 27 Mar 2016 21:39:42 +0100
> Cc: Matthew Leach <matthew@mattleach.net>
> 
> * src/process.c (connect_network_socket): Allow a pre-allocated
> socket descriptor to be used if passed to Emacs, avoiding the call
> to socket() and bind().
> (Fmake_network_process): Allow users to pass in :usepassedsocket
> on the parameter plist to use a socket descriptor that has been
> passed to Emacs.
> (wait_reading_process_output): Call socket() & bind() every time.
> (syms_of_process): New symbol ":usepassedsocket".

Thanks.  I have only one comment: the :usepassedsocket name sounds
weird (why "passed"?).  How about :use-systemd-socket instead?

Oh, and you promised documentation...

Re: [PATCH v2 3/4] Allow network processes to be made with a pre-allocated fd.

[Matthew Leach]

Hi Eli,

Thanks for having another look.

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Matthew Leach <matthew@mattleach.net>
>> Date: Sun, 27 Mar 2016 21:39:42 +0100
>> Cc: Matthew Leach <matthew@mattleach.net>
>> 
>> * src/process.c (connect_network_socket): Allow a pre-allocated
>> socket descriptor to be used if passed to Emacs, avoiding the call
>> to socket() and bind().
>> (Fmake_network_process): Allow users to pass in :usepassedsocket
>> on the parameter plist to use a socket descriptor that has been
>> passed to Emacs.
>> (wait_reading_process_output): Call socket() & bind() every time.
>> (syms_of_process): New symbol ":usepassedsocket".
>
> Thanks.  I have only one comment: the :usepassedsocket name sounds
> weird (why "passed"?).  

I was going for "use the socket that was passed over to Emacs", but yes
I think the name could be better.

> How about :use-systemd-socket instead?

One of the comments on the last version of patches was to try and keep
the name generic, as there could be other programs that pass over
sockets in a similar fashion, such as xinetd.  I could go with
:use-systemd-socket if you want, though?

> Oh, and you promised documentation...

Yes, sorry.  I realised when I sent the patch in that forgot about that.
I'll send over a final patch series that includes the docs, once we've
got the name sorted :-).

Thanks,
-- 
Matt

Re: [PATCH v2 3/4] Allow network processes to be made with a pre-allocated fd.

[John Wiegley]

[-- Attachment #1: Type: text/plain, Size: 1056 bytes --]

>>>>> Matthew Leach <matthew@mattleach.net> writes:

> * src/process.c (connect_network_socket): Allow a pre-allocated
> socket descriptor to be used if passed to Emacs, avoiding the call
> to socket() and bind().
> (Fmake_network_process): Allow users to pass in :usepassedsocket
> on the parameter plist to use a socket descriptor that has been
> passed to Emacs.
> (wait_reading_process_output): Call socket() & bind() every time.
> (syms_of_process): New symbol ":usepassedsocket".

Hi Matthew,

Given that systemd is LGPL-licensed, and used by many GNU/Linux distributions
(even NixOS, which I also use here at home), I welcome your changes to improve
support for it.

I only hope you can offer as much commenting and documentation as possible,
because I've heard systemd is somewhat complex, and I hope we can tame the
part of it that we invite into our codebase. :)

Yours,
-- 
John Wiegley                  GPG fingerprint = 4710 CF98 AF9B 327B B80F
http://newartisans.com                          60E1 46C4 BD1A 7AC1 4BA2

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