[systemd-devel] preparing unit definition for squid – some questions

[Gustavo Sverzut Barbieri]

2010/11/26 Tomasz Torcz <tomek at pipebreaker.pl>:
> On Thu, Nov 25, 2010 at 09:31:55PM -0200, Gustavo Sverzut Barbieri wrote:
>> On Thu, Nov 25, 2010 at 7:43 PM, Tomasz Torcz <tomek at pipebreaker.pl> wrote:
>> > Hi,
>> >
>> >  I'm slowly porting init scripts of software I use to systemd unit files.
>> > It is generally straight-forward, but today Squid made me wonder.
>> >
>> >  Squid is web-caching daemon (proxy) with some pecularities.  It
>> > stores the cache of the internet in some directories on disk.  To
>> > paralleize access, it is recommended to define separate cache_dir for
>> > each hard disk. Also, squid likes 2-level deep folder structure
>> > in each cache_dir, to implement simple hashing and deal with lesser
>> > filesystems.
>> >
>> >  Populating each defined cache_dir can be slow operation, therefore
>> > it is not done automatically.  Fedora's squid script checks if cache_dir
>> > is empty and if so, run the command to create folder hierarchy.
>>
>> IMHO this is totally wrong, we're trying to solve the problem
>> elsewhere. Squid itself should check and generate the missing
>> directories as it will already have to load the configuration file and
>> (probably) the cache directory structure. This is even more true that
>> it shouldn't assume all directories exist if at least one is there
>> (ie: it is not empty, but not all required are there).
>
>  Well, but the Squid won't generate them on normal startup and
> I'm trying to not lose functionality from original sysv script.
> Squid will create directiories when asked to (`squid -z`) but
> it will take time and is special case, hence supplementary unit file.

I don't see how doing this in squid is slower than doing it elsewhere.
If you mean that -z will force squid to not just check $CACHEDIR but
$CACHEDIR/*, then as I said this is the correct behavior and you'd
have to have all of those directories as condition to trigger
recreating the cache, otherwise it may result in runtime failures.

I'd like to see what others think about that, but IMO squid -z should
be used in squid.service

If squid -z will ALWAYS recreate directories, then we could patch it
to just create what is required. Or add that as another flag. One of
the points with systemd is push services to do their things in the
right way, like use configure files to avoid nasty /etc/conf.d or
/etc/sysconfig, to use socket-activation, etc.


>  It's not a precedent. NTPD's sysv script was split during port
> to run ntpdate as separate unit.  udev's was even split into 3
> services.

I can't comment on it, however I find ntpd a bad example for most of
things as it has so many wrong things, like the lack of proper network
handling. And it should be managed by the network system itself
(connman, networkmanager)

udev is an example of the hacks you have to do to support
broken/legacy systems, as udev-settle.service should not be used in an
ideal world, since people would be hotplug-aware and not rely on
"system being ready" as there is no such concept as Kay keeps saying.

-- 
Gustavo Sverzut Barbieri
http://profusion.mobi embedded systems
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