Re: [Nicolas Graves] [PATCH v6 01/10] rde: emacs: Start emacs in --daemon mode, with shepherd and pid-file

[Nicolas Graves]

On 2024-04-12 22:38, Ludovic Courtès wrote:

> Hi Nicolas,
>
> Nicolas Graves skribis:
>
>> As promised to Stefan a few months ago, here's a use case of
>> Shepherd/Emacs implementation that we developped in RDE.
>
> Would be nice to have it in Guix Home!

Something like this seems to work:

(define (emacs-shepherd-service config name)
  (shepherd-service
   (documentation
    (format #f "Emacs server.  Use ~a to connect to it."
            (if (eq? 'server name)
                "@code{emacsclient}"
                (format #f "@code{emacsclient -s ~a}" name))))
   (provision `(,(symbol-append 'emacs- name)))
   (requirement '(emacs))
   (modules '((shepherd support)))  ;for '%user-runtime-dir'
   (start #~(make-systemd-constructor
             (list #$(file-append
                      (home-emacs-configuration-emacs config)
                      "/bin/emacs") #$(format #f "--fg-daemon=~a" name))
             (list (endpoint
                    (make-socket-address
                     AF_UNIX
                     (string-append %user-runtime-dir
                                    "/emacs/" #$(symbol->string name)))
                    #:name '#$(format #f "emacs-~a" name)
                    #:socket-directory-permissions #o700))
             #:log-file (string-append
                         (getenv "XDG_STATE_HOME") "/log"
                         "/emacs-" #$(symbol->string name) ".log")))
   (stop #~(make-systemd-destructor))))

But I'm not sure it's better regarding user experience. On RDE we
implemented a notifier that parses the result of
herd eval root "(and=> (lookup-service 'emacs-server) service-status)"
thus giving a nice "Emacs is currently starting" notification.

This evaluation doesn't seem to work using make-systemd-constructor,
although it has its advantages (indeed launches a frame when available).
It would be nice if service-status could "sync" with
make-systemd-constructor in this case.

I would be happy to send such a patch for Guix (is there already some
patch series on which to graft this?), WDYT @Ludo?

I can also send this in RDE, it simplifies a lot although I'm still not
sure it yields a better user experience. @Andrew?

>> We're using the --daemon option on the Shepherd side to launch the
>> server in the background, include code in Emacs configuration to make it
>> create a pid-file as soon as the server has started, and redefine
>> kill-emacs to be managed by the Shepherd.
>
> Emacs supports systemd-style socket activation so, instead of using a
> PID file, you could use ‘make-systemd-constructor’.
>
> Now, that code in emacs.c is unfortunately implemented via libsystemd
> and thus disabled in Guix.  Using libsystemd in this case is unnecessary
> (and increases the attack surface, as we’ve seen with the xz backdoor):
> it could read the ‘LISTEN_FDS’ and ‘LISTEN_PID’ environment variables
> instead of calling the sd_* functions.
>
>   https://www.freedesktop.org/software/systemd/man/latest/sd_listen_fds.html
>   
> https://www.gnu.org/software/shepherd/manual/html_node/Service-De_002d-and-Constructors.html#index-make_002dsystemd_002dconstructor
>
> Thanks,
> Ludo’.

-- 
Best regards,
Nicolas Graves