Re: [dpdk-dev] [RFC] net/null: add empty promiscuous mode functions

[Andrew Rybchenko <arybchenko@solarflare.com>]

On 10/18/19 2:38 PM, Ferruh Yigit wrote:
> On 10/18/2019 11:13 AM, Bruce Richardson wrote:
>> On Thu, Oct 17, 2019 at 04:33:59PM +0100, Ferruh Yigit wrote:
>>> On 10/17/2019 2:43 PM, Bruce Richardson wrote:
>>>> On Thu, Oct 17, 2019 at 12:05:56PM +0100, Ferruh Yigit wrote:
>>>>> On 10/17/2019 11:51 AM, Andrew Rybchenko wrote:
>>>>>> On 10/17/19 1:47 PM, Ferruh Yigit wrote:
>>>>>>> On 10/17/2019 11:37 AM, Andrew Rybchenko wrote:
>>>>>>>> On 10/16/19 9:07 PM, Ferruh Yigit wrote:
>>>>>>>>> On 10/16/2019 4:46 PM, Ciara Power wrote:
>>>>>>>>>> Adding promiscuous functions prevents sample applications failing when run
>>>>>>>>>> on this virtual PMD. The sample applications call promiscuous functions,
>>>>>>>>>> and fail if this function call returns an error, which occurs when the
>>>>>>>>>> virtual PMD does not support the promiscuous function being called.
>>>>>>>>>>
>>>>>>>>>> This change will be implemented for all virtual PMDs that currently do not
>>>>>>>>>> have existing promiscuous functions. Multicast functions will also be
>>>>>>>>>> added for virtual PMDs to prevent sample application breakages here also.
>>>>>>>>> +Andrew
>>>>>>>>>
>>>>>>>>> With the some ethdev APIs returning error code, some sample applications stop
>>>>>>>>> working with virtual interfaces,
>>>>>>>>>
>>>>>>>>> We can,
>>>>>>>>> 1- update sample applications to ignore the errors
>>>>>>>>> 2- Add dummy dev_ops support to (almost all) virtual PMDs (what this RFC suggests)
>>>>>>>>>
>>>>>>>>> (1) puts us back to before the ethdev APIs updated status, and this may be wrong
>>>>>>>>> for the physical devices case, so I am for this RFC.
>>>>>>>>>
>>>>>>>>> Only perhaps we can have some common empty function and keep assigning that one
>>>>>>>>> to reduce the dummy code, what do you think?
>>>>>>>> I don't like the idea to have common empty/dummy functions.
>>>>>>>> If virtual PMD behaves in accordance with enabled promiscuous mode,
>>>>>>>> it should initialize it properly on init:
>>>>>>>>         eth_dev->data->promiscuous = 1;
>>>>>>>> If so, if application requires promiscuous mode, attempt to enable will
>>>>>>>> do nothing. If application requires non-promiscuous mode, disable will
>>>>>>>> fail and it is good.
>>>>>>> It is technically correct that we can't disable promiscuous mode in virtual PMDs
>>>>>>> but I think mainly we don't really care so it returning error may make the
>>>>>>> applications fail/exit unnecessarily with virtual PMDs.
>>>>>> If I test virtual PMD promiscuous mode, I would prefer enable/disable
>>>>>> callback to say me truth.
>>>>>>
>>>>>> If application really does not care, it should be in the application code.
>>>>> Application can't change this because they may be caring return result for the
>>>>> physical devices.
>>>>>
>>>>> Up until this release these missing dev_ops in virtual PMDs were silently
>>>>> ignored, now APIs are more strict on this (which is good) but to get close the
>>>>> previous behavior for virtual PMDs we need to relax on these features (like
>>>>> saying success on promiscuous disable although it didn't).
>>>>>
>>>> The other variable here is how often an app is going to request promiscuous
>>>> disabling? Given that most ports generally come up in that state anyway,
>>>> and one needs to request enabling it, surely the disable case is relatively
>>>> rare? In that case I'd tend to agree with having disabling it returning
>>>> error for vpmds.
>>>>
>>> Yes disabling most probably rare, but still it will generate an error and
>>> application is failing because of ring PMD promiscuous disable doesn't look
>>> right to me.
>> Well, if an app needs promiscuous mode disabled then having it fail is the
>> right thing to do. If the app doesn't care about promiscuous mode failing,
>> why is it checking the return value at all?
>>
>>> Perhaps application should differentiate between -ENOTSUP error and operation
>>> fail error, but that looks to me adding unnecessary complexity to the app.
>>>
>> Again, does the app care or not? It's probably still better to return
>> correct info to the app in all cases, and then let the app decide how best
>> to handle it.
> My thinking is, application "cares" about the ethdev API return values, but to
> check/test quickly with null/ring PMD perhaps not really care that much abut
> promisc/allmuticast support of these PMDs and let's relax these support of
> virtual PMDs to make life easy.
>
> But eventually the main target is to fix sample applications to run with virtual
> PMDs which has been broken in this release.
> Both approach works,
> a) Implement dummy dev_ops to virtual PMDs to report success
> b) Update ethdev APIs to not call dev_ops if the requested configuration is
> already satisfied and change virtual PMDs to report promisc & allmulticast
> enabled by default. (disable still will have same issue)
>
> Is the consensus option (b)?

Yes.

> btw, the problem exists in high level for the offload support, if the
> application is requesting a specific offload support it fails to run with the
> virtual PMDs since virtual PMDs doesn't support any offloads. Indeed I have same
> suggestion for this case too, relax the virtual PMD by claiming it supports all
> offloads. Because at least for me when I use those virtual PMDs I don't really
> would like to test offloads or the procmisc/allmulticast features ...

It looks like I simply don't understand virtual PMDs usacase.

>>> With a common function shared by all PMDs for both promisc and allmuticast will
>>> add a little code and an easier solution.