Re: [Libvir] Re: Virtual CPU functions
On Tue, Aug 01, 2006 at 07:05:49PM +0200, Philippe Berthault wrote:
>unsigned char *cpuMaps[]; /* 1st dimension = per virtual cpu, 2nd
>dimension = per physical cpu */
...
>>virDomainGetVcpus(pDomain, pVcpuInfos, domInfo.nrVirtCpu,
cpuMaps,
>>oneCpuMapLen);
>>for (vcpu = 0; vcpu < domInfo.nrVirtCpu; vcpu++) {
>> for (cpu = 0; cpu < nbPhysCpus; cpu++) {
>> int byteCpu = cpu / 8;
>> int bitCpu = cpu % 8;
>> int mask = 1 >> bitCpu; /* lowest CPU number is least
>>significant bit as M.Ponceau said */
>>
>
>
>> int cpuUsable = cpuMaps[vcpu][byteCpu] & mask;
>> ...
>> /* or */
>> int cpuUsable = CPU_USABLE(cpuMaps, vcpu, cpu);
>> ...
>>
>
> both are wrong IMHO :-)
>one need to compute the index based on domInfo.nrVirtCpu
>
>
I don't understand why you think both are wrong. The first 'for' loop
index is based on domInfo.nrVirtCpu.
Just a C implem nitpick, but that can lead to interesting debugging
sessions (I think I got beaten by that a couple of time).
Nowhere the compiler can guess that you're accessing a 2 dimentional array
with a row of length domInfo.nrVirtCpu, it's a one dimension array so I
think cpuMaps[vcpu][byteCpu] is equivalent to cpuMaps[vcpu + byteCpu] there
and unless I misunderstood both case that won't work as expected. This is
also why I suggested a macro this can of code is easy to get wrong.
Daniel
--
Daniel Veillard | Red Hat http://redhat.com/
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