Re: [PATCH 2/2] ethtool: add new library to provide ethtool-alike APIs

["Andrew Harvey (agh)" <agh@cisco.com>]

On 6/5/15, 5:47 AM, "Bruce Richardson" <bruce.richardson@intel.com> wrote:

>On Fri, Jun 05, 2015 at 11:25:09AM +0000, Wang, Liang-min wrote:
>> 
>> 
>> > -----Original Message-----
>> > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
>> > Sent: Friday, June 05, 2015 6:47 AM
>> > To: Andrew Harvey (agh)
>> > Cc: Stephen Hemminger; Wang, Liang-min; dev@dpdk.org
>> > Subject: Re: [dpdk-dev] [PATCH 2/2] ethtool: add new library to
>>provide
>> > ethtool-alike APIs
>> > 
>> > 2015-06-04 22:10, Andrew Harvey:
>> > > On 6/4/15, 7:58 AM, "Stephen Hemminger"
>> > <stephen@networkplumber.org> wrote:
>> > > >"Andrew Harvey (agh)" <agh@cisco.com> wrote:
>> > > >> I believe that their is value in this interface for software
>>stacks
>> > > >>not  based on Linux being moved toward DPDK that need simple
>> > > >>operations like  getting the mac address.  Some of these stacks
>>have
>> > > >>a dearth of resources  available and dedicating a core/thread to
>>KNI
>> > > >>to get/set a mac address  is considered excessive. There are also
>> > > >>issues with 32/64 bit kernel  integration  using KNI.  If the
>> > > >>ethtool interface is not the correct interface then  please help
>>me
>> > > >>understand what should/could have been used. If ethtool is
>> > > >>considered 'old  and clunky¹  Stephen's and your input would be
>> > > >>valuable in designing another interface  with  similar properties.
>> > > >>The use-case is pretty simple and there is no plans  for moving
>> > > >>anything back into the kernel on the contrary its the complete
>>opposite.
>> > > >>
>> > > >> ‹ Andy
>> > > >
>> > > >We have DPDK API's to do this, and any added wrappers make it
>>bigger.
>> > > >I don't see why calling your ethtool API is better than calling
>> > > >rte_eth* API.
>> > > >
>> > > >If there is a missing functionality in the rte_ethXXX api's for an
>> > > >application then add that. For example: rte_eth_mac_addr_get()
>> > >
>> > > I am getting somewhat confused by your latest comments.  Your first
>> > > email (referenced below) looked really positive and I found your
>> > > suggestions useful. Your latest post appears to contradict this and
>> > > now the interface was there all the time.  The wrapper façade
>>provided
>> > > by the ethtool library provide a clean separation of concerns and
>>will
>> > > allow people to migrate from not only KNI but in our case from a
>> > > legacy system.  If a software stack has requirements to work with
>> > > multiple IO abstractions then the ethtool approach is attractive. I
>> > > would speculate that many other stacks moving towards dpdk will have
>> > similar issues.
>> > >
>> > > Summarizing, for our use-cases the ethtool interface facilitated our
>> > > adoption to dpdk while allowing us to support our legacy IO
>>abstractions.
>> > 
>> > Stephen and me say the same thing about using the ethdev API.
>> > We don't understand why using a fake ethtool lib would be easier.
>> > Though you are saying it "facilitated [your] adoption to dpdk".
>> > Please could you explain why using an ethtool-like API is easier than
>>using
>> > the existing ethdev API?
>> > In any case, you have to develop a specific backend for DPDK
>>(rte_ethtool
>> > would be also DPDK-specific).
>> 
>> As described earlier in this patch comment reply, there are other
>>ethtool ops that have been implemented.
>> Those ops includes set/get eeprom, set/get pauseparam, set/get
>>ringparam which are not available in the exiting ethdev library.
>> For this release, we focus on releasing some basic functions (btw,
>>mac_addr_set is not available but is covered by this patch).
>> The key reason that this set of library is not released as part of
>>ethdev is the ethtool API dependency on kernel include file.
>> To faithfully carry the ethtool ops and net dev ops API parameters, the
>>ethtool APIs are designed to follow the original definition except
>>avoiding carry kernel states.
>> With that, to support ethtool APIs faithfully, we need to include
>><linux/ethtool.h>.
>> As suggested by many DPDK veterans including Thomas (indicated over
>>your reply), you would prefer these APIs in a separate library.
>> 
>> > 
>> > It seems you already started to use such an ethtool implementation.
>> > Please note that our goal is not to prevent Cisco from upstreaming
>>(evidence
>> > with enic driver integration) but we want to guide you, and others
>>having the
>> > same needs, to the best solution for everybody.
>> > That's why we need to understand what we (or you) are missing.
>> > Maybe that it would be clearer with some code examples (which would
>>go in
>> > the lib documentation if any).
>> > 
>> > Thanks
>
>How about doing this work as a sample application initially, to
>demonstrate how
>an application written using ethtool APIs could be shimmed to use DPDK
>underneath.
>The ethtool to dpdk mapping could be contained in a single header file
>(or header
>and c file) inside the sample app. This would allow easy re-use of the
>shim
>layer, while at the same time not making it part of the core DPDK
>libraries.
>
>Regards,
>/Bruce

This would appear to be the most pragmatic way forward.  It would allow
others to see more of the code and judge its value for themselves. I have
no issues with this approach if others agree.

— Andy