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Re: [libvirt] [PATCHv2] Ignore bridge template names with multiple printf conversions



On 05/05/2015 10:26 AM, Ján Tomko wrote:
> On Tue, May 05, 2015 at 10:14:18AM -0600, Eric Blake wrote:
>> On 05/05/2015 10:05 AM, Ján Tomko wrote:
>>> For some reason, we allow a bridge name with %d in it, which we replace
>>> with an unsigned integer to form a bridge name that does not yet exist
>>> on the host.
>>>

>>> +    if (def->bridge &&
>>> +        (p = strchr(def->bridge, '%')) == strrchr(def->bridge, '%') &&
>>> +        strstr(def->bridge, "%d"))
>>
>> Simpler as:
>>
>> if (def->bridge &&
>>     strstr(def->bridge, "%d") == strrchr(def->bridge, '%'))
> 
> I still don't see it.
> 
> [A] strchr(def->bridge, '%')
> [B] strrchr(def->bridge, '%')
> [C] strstr(def->bridge, "%d"))
> 
> When def->bridge is '%s%s%s%d', [A] points to the first %s, [B] points
> to the %d and so does [C]
> 
> This string would pass the simplified condition (B == C), but not the
> full one (A != C)

Okay, I see your counterargument.  Still, strstr() is pretty expensive
compared to just:

if (def->bridge &&
    (p = strchr(def->bridge, '%')) == strrchr(def->bridge, '%') &&
    p[1] == 'd')

> 
> Jan
>>
>> ACK with that simplification.

at which point p is no longer a dead variable, but I've still reduced
the code complexity.

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

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