Re: [libvirt] [PATCH] Fix up basic migration.

On 05/24/2010 04:34 PM, Eric Blake wrote: > On 05/24/2010 02:20 PM, Chris Lalancette wrote: >>> Sounds good to me - if all entry points filter on all accepted flags, >>> then helper functions can assume that flags are already valid.  As long >>> as the filtering gets done somewhere, we've left the door open for >>> adding future flags while still correctly identifying situations where >>> we are talking to older implementations that can't honor new flags. >>> It's only when there is no flag filtering at all that we've locked >>> ourselves out of easy-to-validate future extensions. >> >> Unfortunately doing this caused a bit of churn in the qemu driver.  qemudDomainMigrate >> takes an unsigned long as flags instead of unsigned int, which required me to create >> two new macros: virCheckFlagsUI and virCheckFlagsUL.  The good news is that with this >> patch in place we are doing more checking of the flags during migration, which is >> probably a good thing.  A new patch is coming up. > > Hmm, since virCheckFlags() is already a macro in the first place, can we > use some sizeof(flags) magic to get it to polymorphically do the right > thing rather than having to invent an alternate spelling? We discussed this on IRC.  Unfortunately I don't think you can use sizeof() directly, since on 32-bit sizeof(unsigned int) == sizeof(unsigned long).  However, what I've done instead is to unconditionally promote flags to an unsigned long and then use %lx.  That seems to work.  I'll post v3 of the patch in a moment.