[dpdk-dev] [PATCH 1/6] net/tap: use correct tap name

[Wiles, Keith]

> On Jan 31, 2017, at 9:38 AM, Yigit, Ferruh <ferruh.yigit at intel.com> wrote:
> 
> On 1/31/2017 3:30 PM, Pascal Mazon wrote:
>> On 01/31/2017 04:28 PM, Ferruh Yigit wrote:
>>> On 1/31/2017 2:23 PM, Pascal Mazon wrote:
>>>> On 01/31/2017 02:06 PM, Ferruh Yigit wrote:> On 1/31/2017 9:42 AM,
>>>> Pascal Mazon wrote:
>>>>>> dev->data->name contains "net_tap", the device driver name.
>>>>> 
>>>>> I see what patch does, just as a note to commit log:
>>>>> 
>>>>> AFAIK, "dev->data->name" is device name, and for this case it is
>>>>> "net_tap#", like "net_tap0", "net_tap1" ...
>>>>> 
>>>>> "dev->data_drv_name" is the driver name which is "net_tap"
>>>> 
>>>> Indeed, dev->data->name is the device name, looking like "net_tap#",
>>>> with number increasing for each vdev.
>>>> I'll put the following commit log line if that's ok:
>>>> 
>>>>     dev->data->name contains the device name, e.g. "net_tap0".
>>>> 
>>>>> 
>>>>>> dev->data->dev_private->name contains the actual iface name,
>>>>>> e.g. "dtap0".
>>>>> 
>>>>> Right, I agree this is correct comparing "dev->data->name"
>>>>> 
>>>>> But the problem is pmd->name is per eth_dev.
>>>>> 
>>>>> If I read code correct, for multiple queue support, each queue pair will
>>>>> create a tap device, so each needs a different name.
>>>>> 
>>>>> So can't just use pmd->name. Need to create a name per queue pair, it
>>>>> can be combination of pmd->name + "_" + queue_id? Or can keep a name per
>>>>> queue pair, instead of eth_dev.
>>>>> 
>>>>> What do you think?
>>>> 
>>>> Actually that's not exactly how it goes.
>>>> Adding a queue to a netdevice requires to open("/dev/net/tun") and setting
>>>> TUNSETIFF (through ioctl) on the resulting fd.
>>>> That's the important part: queues for a given tap device must set TUNSETIFF
>>>> with a common ifreq.ifr_name (in our case, pmd->name).
>>>> 
>>>> This is best explained in the kernel doc, there:
>>> 
>>> Thank you for the clarification.
>>> If so, why PMD keeps a fd per queue?
>>> 
>>> Overall, patch looks good except mentioned detail in commit log.
>>> 
>>> I suggest waiting Keith's patch, and rebase this set on top of it.
>>> 
>>> Thanks,
>>> ferruh
>>> 
>>>> 
>>>> [1]
>>>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/networking/tuntap.txt#n108
>>>> 
>>> <...>
>>> 
>> 
>> I would say it is because dev->{r/t}x_pkt_burst() is done per queue.
>> In these functions, we need to make our read() and write() accesses on the
>> right fd considering the queue we're required to process.
> 
> If fd is same for all queues, it is possible to keep one instance in pmd
> private_data, and access it from queues. I think it is confusing to have
> multiple copy of it, but I see your point.

In my changes I removed the fds[] array as it was not required only the rx/tx_queue has an fd variable.

> 
>> 
>> I'll wait for Keith's patch, then.
> 
> Thanks again.
> 
>> 
>> Best regards,

Regards,
Keith