Allow to redirect logs to file or syslog or both

[foxcpp]

Global directive?

log <targets...>

log stderr

Write to stderr (default).

log file_name

Write to file.

log syslog

Send messages to local syslog daemon.

Can be combined:

log stderr syslog /var/log/maddy/maddy.log

[foxcpp]

Should we handle some signal (perhaps SIGUSR1 or SIGUSR2) as a request to reopen the log file? This will allow the logrotate daemon to not restart maddy to correctly perform the rotation.

[emersion]

Should we handle some signal

Not a fan of this, we'll end up with more features we want than signals available. Any idea how other daemons handle this?

Maybe people who want this should use stdout + a thin wrapper process that does what you said.

[foxcpp]

Not a fan of this, we'll end up with more features we want than signals available. Any idea how other daemons handle this?

Other daemons either have a full-blown IPC interface using Unix sockets or offer only one-two basic functions like "reload config" using SIGUSR1/SIGUSR2 signals.

Speaking of available signals, since Linux 2.2 we have 31 signals for application use (SIGRTMIN-SIGRTMAX, excluding two possibly used by glibc internally (let's say we use sqlite3).
Signals from this range also have some interesting properties, see signal(7)

[emersion]

"reload config" using SIGUSR1/SIGUSR2 signals

I'm okay with that.

Speaking of available signals, since Linux 2.2 we have 31 signals for application use

This is not POSIX though.