Re: [Xen-devel] [PATCH] x86: fix off-by-one in nr_irqs_gsi calculation

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 26.07.12 at 17:31, Keir Fraser <keir@xxxxxxx> wrote:
> On 26/07/2012 16:06, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
> 
>> highest_gsi() returns the last valid GSI, not a count.
>> 
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> Why not "nr_irqs_gsi = max(nr_irqs_gsi, highest_gsi()+1)"?

While I think x = max(y, z) is fine, I generally find x = max(x, y)
pretty useless - what's the point of assigning a value to itself?
This is __init code, so code size considerations probably don't
matter, but I'd still like to not encourage inefficient code like this
to be used elsewhere by giving a bad example...

Jan

>> --- a/xen/arch/x86/io_apic.c
>> +++ b/xen/arch/x86/io_apic.c
>> @@ -2531,7 +2531,9 @@ void __init init_ioapic_mappings(void)
>>          }
>>      }
>>  
>> -    nr_irqs_gsi = max(nr_irqs_gsi, highest_gsi());
>> +    i = highest_gsi();
>> +    if ( i >= nr_irqs_gsi )
>> +        nr_irqs_gsi = i + 1;
>>  
>>      if ( max_gsi_irqs == 0 )
>>          max_gsi_irqs = nr_irqs ? nr_irqs / 8 : PAGE_SIZE;
>> 
>> 
>> 
>> _______________________________________________
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>> Xen-devel@xxxxxxxxxxxxx 
>> http://lists.xen.org/xen-devel 




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