Do some basic compatibility checking when installing a new server

[disorder] / README.reload

The effect of "disorder reconfigure"
====================================

This is current rather vaguely defined and implemented.  This file
will lay out what you can and cannot change over a reconfigure.  Any
other changes will require a full server restart.

The situation is gradually improving; this file tracks the current
state.

* Options that might have to remain the same across restart

Arguably if there is anything in this section then that's a serious
bug!

** alias (enforced at reload only)

This defines how aliases are inserted into the track database.  Need
to think about how changing it will affect things.

** namepart

Probably affects alias construction.

** stopword

The search database will have to be rebuilt from scratch.  This is
do-able but AFAIK we don't detect it.

** user (enforced at reload only)

All the files will be owned by the wrong user!

* Options that must remain the same across reload

Some things will just require a restart.  We should either enforce
this (refusing to accept modified configurations that purport to
change them) or explicitly ignore it.

** home (enforced at reload)

We absolutely cannot accept changing our state directory.

** lock (generates a deprecation warning)

Liable to be removed anyway.

** nice_speaker (generates a warning)

You can't renice a running speaker to make it less nice (and we don't
try to make it more nice).

* Options that ought to be changable across reload but aren't

These options need some work somewhere to be changeable just by a
reload.

** api

The main server will cope fine with this changing.  The speaker will
ignore the change however.

** broadcast

The speaker will ignore the change.

** broadcast_from

The speaker will ignore the change.

** collection

If the set of collections change we ought to initiate a rescan.

** device

The speaker will ignore the change.

** multicast_loop

The speaker will ignore the change.

** multicast_ttl

The speaker will ignore the change.

** pause_mode

The speaker will ignore the change.

** sample_format

The speaker will ignore the change.

** speaker_command

The speaker will ignore the change.

* Options that can be changed across reload

These options can be changed at reload and it should just work.

** authorization_algoritm

** channel

** default_rights

** listen

** mixer

** new_bias

** new_bias_age

** new_max

** nice_rescan

Wouldn't affect an already-running rescan, but reload already cancels
and restarts the underway rescan anyway.

** noticed_history

** reminder_interval

** remote_userman

** replay_min

** signal

** sox_generation

** scratch

* Options that can change, but with a caveat

These options can be changed at reload but there is some caveat about
this (which ought to be documented, and in some cases is).

** plugins

Plugin path.  You can change the plugin path but an already-loaded
plugin may stay loaded.

** cookie_key_lifetime

Only affects subsequently generated keys - cannot shorten (or extend)
the lifetime of the current key.

** cookie_login_lifetime

Only affects subsequently generated cookies - cannot shorten (or
extend) the lifetime of already-generated cookies.

** history

The history might not shorten until it's next written.

** player

Won't affect running players or decoders.

** queue_pad

Won't shrink the queue.

** tracklength

Won't affect already-computed lengths.

* Implementation Considerations

A likely change is that the speaker will be created on demand and
stopped when idle.  Some changes will still be handled via SM_RELOAD
but others may require the speaker to quit and restart.