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

[Nicolas Graves via "Development of GNU Guix and the GNU System distribution." <guix-devel@gnu.org>]

On 2024-04-13 16:20, Nicolas Graves wrote:

> 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!
>
> I am commited to merge RDE contributions upstream when this is possible,
> I will when it's mature enough / adapted for Guix ;)
>
>>
>>> 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, that is precisely the feedback I was looking for.
>
> Maybe some feedback on the Emacs side about this? There are indeed very
> few places where systemd sd_* functions are called in emacs.c, should we
> try and re-implement them instead of using the library as is? Would that
> be a contribution Emacs devs would be interested in? That would
> definitely be beneficial for Emacs on Guix as highlighted by Ludo'.

For the Guix side: it seems to be possible without Emacs source code
change and by using elogind instead of systemd, there seems to be some
code in configure.ac to handle this case. Will try this.

>
>>
>> Thanks,
>> Ludo’.

-- 
Best regards,
Nicolas Graves