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

[Timo Sirainen]

On 23.4.2013, at 17.58, Rickard Nilsson <rickard.nilsson at telia.com> wrote:

> 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.

Sounds like a rather generic problem in nixos. Maybe there could be generic way to handle this for other packages too, like maybe creating a whole new directory somewhere (e.g. under /var) that has symlinks to all the installed plugins?

> 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 }".

You can preserve environments by adding them to import_environment setting.

> 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.

I'd rather make those plugin dirs configurable, since it only adds new settings that just about nobody changes (and perhaps I shouldn't have added mail_plugin_dir setting either in the first place).