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To: "Wiles, Keith" <keith.wiles@intel.com>,
"Yigit, Ferruh" <ferruh.yigit@intel.com>
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From: Pascal Mazon <pascal.mazon@6wind.com>
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Date: Tue, 31 Jan 2017 16:44:30 +0100
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Subject: Re: [dpdk-dev] [PATCH 1/6] net/tap: use correct tap name
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On 01/31/2017 04:44 PM, Wiles, Keith wrote:
>
>> On Jan 31, 2017, at 9:38 AM, Yigit, Ferruh <ferruh.yigit@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.
Sounds good to me.
Ferruh, just to make sure we're on the same page, in multiqueue, there
is definitely a different fd for each queue.
>
>>
>>>
>>> I'll wait for Keith's patch, then.
>>
>> Thanks again.
>>
>>>
>>> Best regards,
>
> Regards,
> Keith
>
--
Pascal Mazon
www.6wind.com