On Wed, Nov 2, 2011 at 3:12 PM, Corey Bryant <cor...@linux.vnet.ibm.com> wrote:
> On 11/02/2011 06:58 AM, Stefan Hajnoczi wrote:
>>
>> On Tue, Nov 1, 2011 at 5:13 PM, Corey Bryant<cor...@linux.vnet.ibm.com>
>> wrote:
>>>
>>> +static bool has_vnet_hdr(int fd)
>>> +{
>>> + unsigned int features = 0;
>>> + struct ifreq ifreq;
>>> +
>>> + if (ioctl(fd, TUNGETFEATURES,&features) == -1) {
>>> + return false;
>>> + }
>>> +
>>> + if (!(features& IFF_VNET_HDR)) {
>>> + return false;
>>> + }
>>> +
>>> + if (ioctl(fd, TUNGETIFF,&ifreq) != -1 || errno != EBADFD) {
>>> + return false;
>>> + }
>>
>> I don't understand this expression. We want TUNGETIFF to fail with
>> EBADFD, otherwise we return false. What is this trying to do?
>>
>> Why do we even need TUNGETIFF after TUNGETFEATURES succeeded and we
>> were able to check out the IFF_VNET_HDR flag?
>>
>> Stefan
>>
>
> I don't think the TUNGETIFF call is necessary. It verifies that the tap
> device doesn't already exist. The ensuing TUNSETIFF call should already
> cover this.
Thanks for explaining. It would be nice to comment this or drop the
if statement entirely if you are sending another revision of this
patch series.
Stefan
