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Re: [linux-lvm] FW: LVM on Linux



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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> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html

-- 

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 Sistina com                           +49 2626 141200
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