[Dovecot] Feature request: Configure CONFIG_MODULE_DIR and AUTH_MODULE_DIR at runtime

[Rickard Nilsson]

Hi!

I am running dovecot 2.1.16 on NixOS (http://nixos.org), and I have been  
fighting the dynamically loaded dovecot modules/plugins a bit.

The problem is that in Nix/NixOS all packages are completely isolated from  
each other (each package has a separate /lib, /libexec, /bin etc, with  
only its own files in it). So dovecot has all its modules under  
/nix/store/xxx-dovecot/{lib,libexec}/dovecot, and the Pigeonhole modules  
are under /nix/store/yyy-pidgeonhole/{lib,libexec}/dovecot.

Now, dovecot wants to load modules only from one directory, so I created a  
"virtual" package that unifies all modules in  
/nix/store/zzz-dovecot-plugins/{lib,libexec}/dovecot. I can then use this  
directory as the "mail_plugin_dir" setting in dovecot.conf. This works  
fine, dovecot can then find the "sieve" mail plugin.

The problem is the service and auth modules, that dovecot tries to load  
 from the compile-time set MODULE_DIR/{settings,auth}. This is a problem  
for me, because I can't set the module path during compilation since that  
introduces a circular dependency between the dovecot package and the  
virtual dovecot-plugins package.

I have solved this by hacking dovecot to read an environment variable,  
DOVECOT_CONFIG_MODULE_DIR, in the config_parse_load_modules function. This  
way I can inject my module path during runtime. But this only works for  
the master process, not the config process which seems to reset its  
environment (I assume it does this when dropping privileges). So I did  
another hack which lets me pass an argument to the config process which  
contains the module path. I can then set this argument in dovecot.conf by  
"service config { executable = config /my/module/path }".

These hacks work, and I can now use both the sieve mail plugin and the  
sieve service. I have attached the patch, but this is not a request to add  
it to the source. My hack is a hack because I don't know enough about the  
inner workings of dovecot to solve it in a good way. Rather, I'm asking  
for some way to configure the module path in dovecot, either as an  
argument to the master process or as a setting in dovecot.conf. A bonus  
would be the ability to specify several paths that dovecot would search,  
then I can do away with my virtual module package.



Best regards,
   Rickard Nilsson
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