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

[Bruce Richardson <bruce.richardson@intel.com>]

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