Re: [RFC PATCH] Split udev_sysfs.c to leave out caches from libudev

[Alan Jenkins <alan-jenkins@tuffmail.co.uk>]

Kay Sievers wrote:
> On Tue, Sep 2, 2008 at 13:09, Alan Jenkins <alan-jenkins@tuffmail.co.uk> wrote:
>   
>> udev_sysfs.c device and attribute value caches are only appropriate for
>> short-lived processes, like udev-event and usbid.  In long lived processes
>> they would fill up with stale data.
>>     
>
> Sure, the cache was never coded to be used in threaded programs.
>
>   
>> Fortunately libudev doesn't use these caches.
>>     
>
> For good reason, yeah. And it will not, at least not in its current state.
>
>   
>> But this should be made
>> explicit to guard against future changes.  Let's move the caches into a
>> separate file, with its own initialization and cleanup functions.
>>     
>
> Wouldn't it be nicer to create a sysfs_cache object, which is passed
> to all these functions? The "cheap" tools can just use NULL there, but
> any possible user could have more than one instance of the cache. The
> cache is really needed if you do thousand of rule compares against a
> sysfs value, over and over. I guess we should start changing the stuff
> to work with local vars, instead of moving the current global stuff to
> a different file?
>   

Good point.  That helps make the cache usage more explicit, and it's
much nicer for my purposes as well.  (I had blindly converted the global
cache variables to per-thread variables, without touching the callers).

Ok.  To keep the existing behaviour where udev_rules_get_run() reuses
the cache from udev_rules_get_name(), they both need a sysfs_cache
parameter.  Then I have to change test-udev and udevtest as well as
udevd - no point having test programs if they use different code paths. 
I'll see what that looks like then and resend.

Thanks
Alan