Extended file stat: Splitting file- and fs-specific info?

David Howells dhowells at redhat.com
Thu May 10 03:14:11 MDT 2012

Dave Chinner <david at fromorbit.com> wrote:

> > Also, do Dave Chinner's ideas for indicating five I/O parameters want to be
> > 32-bit numbers?  Larger?  Smaller?  Can they be log2?
> Definitely 32 bit, IMO, as it's not uncommon to see optimal IO sizes
> in the tens of megabytes on large, high bandwidth storage systems.
> As for being log2 - that's just making it more complex to use and
> making code ugly - we'd have to convert to log2 in kernel, then
> convert back in every single application....

ilog2() in the kernel uses the CPU's bit-scan instruction if it has one and
converting back is just a bitshift operator.

But let's go with 32-bit fields for the moment.  I presume we aren't worried
about a driver that wants to do a 4GB transfer...


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