On Thu, 10/30 10:09, Arthur Gautier wrote: > On Wed, Oct 29, 2014 at 09:28:52AM +0800, Fam Zheng wrote: > > On Tue, 10/28 16:00, Stefan Hajnoczi wrote: > > > On Thu, Oct 23, 2014 at 10:03:25AM +0200, Markus Armbruster wrote: > > > > Michael Tokarev <m...@tls.msk.ru> writes: > > > > > > > > > On 10/22/2014 05:25 PM, Arthur Gautier wrote: > > > > >> We can not rely on int cast to get a correct number of cylinders. The > > > > >> cylinders information was wrong in 49.9999% of cases. > > > > >> > > > > >> This ensures the cylinders always gets the ceiling value. > > > > > > > > > > Good thing, especially the good probability :), and also a good patch > > > > > which comes with a test. > > > > > > > > > > But I wonder if anything can break this way? Migration, windows guest > > > > > being unable to find its partitions, something else? > > > > I'd like to hear an answer to this question too, so we know why it's right > > and > > worth to have. > > > Sincerely, I didn't tried myself. > > > > > > > > > > > And more. What-if our drive size in cylinders will be larger than > > > > > the size in bytes? The proposed div_round_up() will increase number > > > > > of cylinders, so size in CHS will be larger than size in bytes. Maybe > > > > > there was a reason why originally the size in cylinders was calculated > > > > > by truncating extra fractional part? What-if guest will try to access > > > > > the very last CHS which is incomplete? > > > > I don't remember a reason why truncating (I doubt there is any), OTOH I'm > > not > > sure what is the right thing to do if the guest tries to write to the last > > incomplete CHS either. > > > > Fam > > Maybe we can expand the disk to the size matching cylinders * sectors * > sector_size and issue a warning to the user? This way it will always be > safe. >
Possible, but I don't know if it's worth it. Could you explain what doesn't work now, in order to show *why* you need this change? Thanks, Fam
