Re: [PATCH v3] Add systemd socket launching support

[Matthew Leach <matthew@mattleach.net>]

Hi Stefan,

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> +#include <systemd/sd-daemon.h>
> [..]
>> +#ifdef HAVE_SYSTEMD
>> +      /* Read the number of sockets passed through by systemd. */
>> +      systemd_socket = sd_listen_fds(1);
>
> AFAICT, this is the core of the dependency to systemd.

Yes, that's correct.  There is also a call to `sd_is_socket' just below
this line.

> Could you explain to us, how the socket information is actually
> passed?  Is it passed via an env-var?

I believe so, I'm not a systemd expert, though.  Looking at the man page
for the sd_listen_fds:

Internally, sd_listen_fds() checks whether the $LISTEN_PID environment
variable equals the daemon PID. If not, it returns
immediately. Otherwise, it parses the number passed in the $LISTEN_FDS
environment variable, then sets the FD_CLOEXEC flag for the parsed
number of file descriptors starting from SD_LISTEN_FDS_START. Finally,
it returns the parsed number.

HTH,
-- 
Matt