[libvirt] [PATCH v2] domain: fix parsing of memory tunables on 32-bit machines

[Eric Blake]

On 10/31/2014 12:20 AM, Martin Kletzander wrote:
> On Thu, Oct 30, 2014 at 02:00:34PM -0600, Eric Blake wrote:
>> Commit 6c9a8a4 (Oct 2014) exposed a long-standing issue on 32-bit
>> machines: code related to virDomainSetMemoryParameters has always
>> been documented as using a 64-bit limit, but it was implemented by
>> calling virDomainParseMemory which enforced an 'unsigned long'
>> limit.  Since VIR_DOMAIN_MEMORY_PARAM_UNLIMITED capped to a
>> long is -1, but virDomainParseScaledValue no longer accepts
>> negative values, an attempt to use 2^53-1 as a hard memory limit
>> started failing the testsuite.  However, the problem with capping
>> things artificially low has existed for much longer - ever since
>> commits 4888f0fb and 2e22f23 (Mar 2012) switched internal tracking
>> from 'unsigned long' to 'unsigned long long' (prior to that time,
>> the cap was a side-effect of the choice of types).  We _have_ to
>> cap the balloon memory values, (no thanks to baked in 'unsigned long'
>> of API such as virDomainSetMaxMemory or virDomainGetInfo with no
> 
> Oh, this is why it needs to be capped.  That makes sense.  And great
> to have it in the comment next to those variables!

Comments can make a world of difference :)

>> + * exceed VIR_DOMAIN_MEMORY_PARAM_UNLIMITED once scaled; additionally,
>> + * if CAPPED is true, the value must fit within an unsigned long (only
>> + * matters on 32-bit platforms).  Return 0 on success, -1 on failure
>> + * after issuing error.  */
> 
> The last sentence (Return ...) could be in its own paragraph even
> though our documentation is not created for these functions.
> 
> ACK with that and safe for freeze and also build-breaker for 32-bit
> machines.

Tweaked and pushed.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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