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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.

-- 
Chris Lalancette


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