Il 30/07/2012 15:53, Eric Blake ha scritto:
> On 07/30/2012 07:40 AM, Paolo Bonzini wrote:
>> Il 28/07/2012 15:43, Eric Blake ha scritto:
>>>>> + if (granularity < 512 || granularity > 1048576 * 64) {
>>>>> + error_set(errp, QERR_INVALID_PARAMETER, device);
>>>>> + return;
>>>>> + }
>>>>> + if (granularity & (granularity - 1)) {
>>>>> + error_set(errp, QERR_INVALID_PARAMETER, device);
>>>>> + return;
>>> In the XBZLRE migration series, we decided to round the users input down
>>> to a power of two instead of reject it. Should we do that here?
>>
>> I can certainly do that, but do you have a pointer to the discussion so
>> that I can understand the rationale?
>
> https://lists.gnu.org/archive/html/qemu-devel/2012-05/msg02421.html
Hmm, a buffer size (the cache size in the case of XBZRLE) is different
however. There is no reason in principle why it needs to be a power of
two (except if you know how the hash table is implemented, or something
like that). For example, the buf_size argument in this series does
indeed support a non-power-of-two size.
Requesting a granularity to be a power-of-two shouldn't be surprising to
anybody who has an idea of what a bit shift is and how it is used...
Paolo
