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Re: Locking in disk(9) api
On Fri, Jan 01, 2010 at 02:10:53PM +0000, David Laight wrote:
> 1) the 'disk busy' count, this isn't a statistic so needs locking.
> 2) cumulative counts of transfers and bytes, these are just stats so
> don't necessarily need locking. The most likely 'error' is that one
> of the addittions is lost, this is really below the noise floor.
> A slight worry might be an error when a multi-word value wraps (eg
> a 64bit counter on a 32bit machine that has no double-word memory
> accesses). This is probably statistically unlikely enough to be
> ignored as well.
It may not be documented but it's the driver's responsibility to provide
locking for these. Have a look at ccd for an MP-safe example.
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