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Re: [dm-devel] [PATCH] libmultipath/discovery: read sysfs files uncached



On 04/02/2013 11:00 PM, Christophe Varoqui wrote:
> On mar., 2013-04-02 at 16:28 +0200, Sebastian Riemer wrote:
>> The libudev function udev_device_get_sysattr_value() reads sysfs
>> attributes cached. This is useless for checking a device state.
>> There we want to see if it changes.
>>
>> Unfortunately, libudev doesn't provide an uncached variant. This
>> is why we have to reimplement the functionality and some libudev
>> internal functions here.
>>
> Hannes,
> 
> as the commit 058a0044cb2ab7cac6f7c3e2e17b16e00b5e57fa author, would you
> sign-off this patch ? Or do you prefer the issue addressed on the udev
> side ...
> 
Hmm; this is not the only issue we have with libudev.
_Setting_ of sysfs attributes is also a problem (I just send a patch
to Kay for this).
However, having to duplicate things feels like a waste; I'd rather
have it implemented at the libudev side.

The problem with this patch is that we're bypassing the cache of
libudev; so any _other_ application using libudev would still be
reading the stale value.

I'd very much prefer to have a 'uncached' variant (or adding another
argument 'force') which would force libudev to always read the
current value but also adding it to the internal cache for the
benefit of other applications.

Kay?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare suse de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)


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