[pacman-dev] Hooks for pacman

[Aaron Griffin]

On Thu, Jan 22, 2009 at 6:29 PM, Allan McRae <allan at archlinux.org> wrote:
> Aaron Griffin wrote:
>>
>> On Thu, Jan 22, 2009 at 9:15 AM, Allan McRae <allan at archlinux.org> wrote:
>>
>>>
>>> Hi all,
>>>
>>> A new feature I am ever so slightly obsessed about at the moment is the
>>> possibility of having hooks in pacman for doing common tasks in install
>>> files.  e.g.  adding info pages to directory, updating font/icon/.desktop
>>> cache, gconf stuff...
>>> So, how would this be implemented?   Here is my outline:
>>>
>>> Two types of hooks would be needed for both install and remove.  One type
>>> that is run for every matching file (e.g. info install) and one type that
>>> is
>>> run once per transaction (e.g. font cache update).  These could be stored
>>> in
>>> /etc/pacman.d/hooks/ with an index of hooks in /etc/pacman.d/hooks.conf.
>>>  The .conf file could look something like:
>>>
>>> [add]
>>> PerFile = infopage    /usr/share/info/
>>> PerTrans = fontcache    /usr/share/fonts/
>>>
>>> [remove]
>>> ...
>>>
>>> That needs improvement, but that covers the information that needs
>>> presented
>>> - whether the hook is run per file or per transaction, the name of the
>>> hook
>>> and the directory whose files set off this hook.  Maybe the conditions
>>> that
>>> set the hook off should be in the actual hook file.
>>>
>>> I guess the actual hook would look look just like:
>>>
>>> hook()
>>> {
>>> do stuff here...
>>> }
>>>
>>> I figure we must already generate a list of all the files being
>>> added/removed during conflict checks, so we would "just" need to scan
>>> that
>>> list for what hooks need to be run and actually run them.
>>>
>>> Anyway, I thought I would post this idea here so I could get more
>>> feedback
>>> on the implementation and maybe convince someone to code it...
>>>
>>
>> This is much better than the ideas Dan and I fleshed out last time we
>> talked about this. One or two nitpicks, though:
>>
>> a) [add] and [remove] seem to simple. How about [AddHooks] and
>> [RemoveHooks]?
>> b) It'd be nice to use fnmatch patterns (globs) for the file paths.
>> c) Instead of a function, it makes more sense to just make a script
>> that takes the files as args, and only run it if it is executable
>> (assume -x is disable)
>> Other than that, I really like the PerFile and PerTrans distinction.
>>
>
> All good suggestions.  I went for the function idea so I could reused code
> for running install scripts.  I have never look at that code so I don't know
> whether that would be a good or bad idea.

The code simply runs bash and does the following:
   . /my/install/scriptlet; post_install $version

Note the dot and semicolon are newer. The previous code didn't have it
- thus the reason why you see the "op=$1" malarky in older scriptlets.

> Thinking about this some more, per transaction hooks really only need ran
> per transaction...   I.e. there is probably no need for the distinction
> within [AddHooks] of PerFile and PerTrans.  All the examples I used for run
> once hook will look the same for both add and remove.   Instead, we could
> have [AddHooks], [RemoveHooks] and [TransHooks].

That's a good point - the per-transaction hooks are probably able to
handle added AND removed files. If not, it is a bash script, so i'm
sure something could be done. Worst case scenario, a very complex hook
could use all three - write some info to a temp file on add or remove,
then use the file in the trans hook.

>> When modifying the config parsing, can you ensure 'Include' works
>> here? That would allow us to ship some stock hooks for info files and
>> the like, and users would simply include them.
>>
>
> Can you provide an example of what you think the config would look like.   I
> have a fair guess at what you mean but clarification would be good.

[AddHooks]
Include = /etc/pacman.d/hooks/gnome-hooks
...

# gnome-hooks
PerFile = mime-database-stuff
PerFile = scrollkeeper-stuff
PerFile = update-desktop-db

I guess with the removal of PerFile/PerTransaction, this gets a little
more weird... perhaps we could allow multiple sections of the same
name to add to the previous one. That is:

[AddHooks]
something

Include = /etc/pacman.d/hooks/gnome-hooks
...

#gnome-hooks
[AddHooks]
above-gnome-stuff

[RemoveHooks]
more-stuff