[linux-lvm] FW: LVM on Linux
Heinz J. Mauelshagen
Mauelshagen at sistina.com
Wed Jul 18 15:01:16 UTC 2001
On Wed, Jul 18, 2001 at 09:16:39AM +0100, Joe Thornber wrote:
> On Tue, Jul 17, 2001 at 12:23:18PM -0700, Ralph Jennings wrote:
> > On Tue, Jul 17, 2001 at 05:40:08PM +0100, Joe Thornber wrote:
> > [snip]
> > > Here there's one % that we can't get rid of (we could also do chunk =
> > > sector - (pe_size * index)), for the simple fact that the number of
> > > stripes is not a power of 2, so we can't replace with shifts and masks.
> > >
> > > I just had a chat with one of the EVMS guys, EVMS *does* have this
> > > exact same problem.
> > >
> > > Should we restrict stripes sets to powers of 2 ?
> > [snip]
> >
> > Why not just make a mod function?
> >
> > Preceeding code not tested, but should work?
> > It's been a while since I wrote C code.
> >
> > BTW, what is a u64 (unsigned 64bit integer) in C called?
> > Is there any uniform cross platform way to say it (like
> > u64 perhaps)?
>
> long long ?
u64 = unsigned long long :)
>
> >
> > u64 mod_64(u64 number, u64 modNum) {
> > while (number > modNum) {
> > number -= modNum;
> > }
> > return number;
> > }
>
> I'd like to see the flames if I put this into the driver :) The map
> function is called on every io block to an LVM device, it needs to be
> quick ! Since we know modNum is smallish, certainly less than 2^32,
> and 'number' is 64 bit we could be running around your loop a few
> times :)
Yep.
>
> On a more serious note this function should be provided by the
> compiler, since it supports the 64 bit type. I guess it is normally
> implemented in a function that gets linked automatically - it would still
> be good to get rid of it.
True.
>
> - Joe
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--
Regards,
Heinz -- The LVM Guy --
*** Software bugs are stupid.
Nevertheless it needs not so stupid people to solve them ***
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Heinz Mauelshagen Sistina Software Inc.
Senior Consultant/Developer Am Sonnenhang 11
56242 Marienrachdorf
Germany
Mauelshagen at Sistina.com +49 2626 141200
FAX 924446
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