[libvirt] [PATCH] conf: use proper maximum for parsing memory values

Eric Blake eblake at redhat.com
Thu Oct 30 16:09:03 UTC 2014


On 10/30/2014 09:55 AM, Eric Blake wrote:
> On 10/30/2014 09:49 AM, Martin Kletzander wrote:
>> The value is stored in unsigned long long, so ULLONG_MAX is the proper
>> upper limit to use.
> 
> No, it's not.
> 
>>
>> Signed-off-by: Martin Kletzander <mkletzan at redhat.com>
>> ---
>> Even though this is a build-breaker (for 32bit systems
>> memtune-unlimited fails to parse), I'm not pushing it as one because
>> it feels odd that such change wouldn't break anything else.
> 
> What's the compile failure?  This patch is intentionally trying to fit
> the largest value that will fit in an unsigned long when scaled by
> kilobytes, while still parsing by bytes.  Thus, on 64-bit machines, you
> can parse 0xffffffffffffffff bytes, then scale down by 1024 and store in
> unsigned long; on 32-bit machines, your maximum has to be limited to
> 0xffffffff*1024 bytes before scaling back down.

Sounds like the real bug is in the memtune-unlimited test.  2^53-1 is
the maximum memory for a 64-bit host, but invalid on a 32-bit host.  Any
interface that uses 'unsigned long' as its capping point has to have
different maximum limits on 32-bit hosts.

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

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