Re: [dpdk-dev] [PATCH v1] net/tap: explain how to compile eBPF C file

[Thomas Monjalon <thomas@monjalon.net>]

04/07/2018 21:47, Ferruh Yigit:
> On 6/12/2018 3:02 PM, Ophir Munk wrote:
> > Please note that other than cloning iproute2 we also need to install clang and llvm tools versions 3.7 and upper.
> > Not sure there are clang and llvm packages of the required versions for the common distributions. 
> > I compiled the tools source code and installed them manually.
> 
> Hi Keith, Thomas,
> 
> What do you suggest on this patch?
> 
> The "tap_bpf_program.c" is already withing the tap pmd this patch improves the
> doc about how to compile it, although it may not be so user friendly as Keith
> pointed, I believe better to get doc improvement here.
> 
> And there is a code update "+#include "bpf_api.h", which includes a iproute2
> header, I am not sure about this one and how to manage this dependency.

If you feel it needs some improvement, we can postpone it for 18.11.
The most important is to have a patch to reference when somebody asks.

It can be improved and merged later, no pressure.


> >> -----Original Message-----
> >> From: Wiles, Keith [mailto:keith.wiles@intel.com]
> >>
> >>> On Jun 12, 2018, at 8:44 AM, Thomas Monjalon <thomas@monjalon.net>
> >> wrote:
> >>>
> >>> 12/06/2018 15:33, Wiles, Keith:
> >>>>
> >>>>> On Jun 12, 2018, at 7:58 AM, Thomas Monjalon
> >> <thomas@monjalon.net> wrote:
> >>>>>
> >>>>> 12/06/2018 14:36, Wiles, Keith:
> >>>>>>
> >>>>>>> On Jun 12, 2018, at 7:26 AM, Thomas Monjalon
> >> <thomas@monjalon.net> wrote:
> >>>>>>>
> >>>>>>> 11/06/2018 18:35, Wiles, Keith:
> >>>>>>>>
> >>>>>>>>> On Jun 11, 2018, at 11:06 AM, Ophir Munk
> >> <ophirmu@mellanox.com> wrote:
> >>>>>>>>>
> >>>>>>>>> This commit explains how to manually compile the C source file
> >>>>>>>>> tap_bpf_program.c into an ELF file using the clang compiler.
> >>>>>>>>> The code in tap_bpf_program.c requires definitions found in
> >>>>>>>>> iproute2 source code. This commit suggests cloning the iproute2
> >>>>>>>>> git tree and include its path in the clang command. It also adds
> >>>>>>>>> inclusion of file bpf_api.h (required for eBPF definitions)
> >>>>>>>>> which is located in iproute2 source tree. For more details refer to
> >> TAP documentation.
> >>>>>>>>> This commit is related to commits [1] and [2].
> >>>>>>>>
> >>>>>>>> Normally I would have suggested that eBPF be disable in the TAP
> >> driver as it requires external code and programs, but that ship has sailed.
> >>>>>>>
> >>>>>>> The external programs are required only to generate new
> >>>>>>> instructions, changing the behaviour of the BPF program.
> >>>>>>> Currently, the instructions for RSS behaviour are provided.
> >>>>>>>
> >>>>>>>> I would like to see building the tap_bpf_program.o as a target in the
> >> Makefile, this way the developer can just run the ‘make bpf_program’ target
> >> and it would be simpler and less error prone.
> >>>>>
> >>>>> As explained in the documentation, for now there is a dependency on
> >>>>> iproute2 for the compilation of this BPF program.
> >>>>> So we cannot make it as simple as a "make command".
> >>>>> Probably that we can rework it to change the dependency.
> >>>>> I heard there are some good BPF libraries available now?
> >>>>
> >>>> Well the dependence of iproute2 is really no different then requiring say
> >> libnuma, they just have to pull the code first to type the ‘make bpf_program’
> >> right?
> >>>
> >>> The iproute2 dependency is different because it is not a library.
> >>> The .h file is never packaged.
> >>> So we need to download the sources and set -I to this directory.
> >>
> >> To eliminate the -I problem the clone could be done inside the tap directory
> >> and -I ./iproute2/include used, right?
> >> The make target could even clone the code into the tap directory, which
> >> means we can solve these problems you are pointing out.
> >>
> >> Go ahead and do what you want here, but making it harder for the developer
> >> should not be our normally mode of operation.
> >>
> >>>
> >>>
> >>>> If that is the case then a make target make sense to me. If iproute2 is not
> >> found then an error, right?
> >>>
> >>>
> >>>>>>> For this to happen, we need to improve the tools.
> >>>>>>
> >>>>>> In what way do we need to improve the tools and which tools are we
> >> talking about. Building the .o file below appears to be a simple set of
> >> command lines. I have a question in my original email about what tool.
> >>>>>
> >>>>> The .o file is only the an intermediate file.
> >>>>> The next step (numbered as 5 in this patch) is to extract the
> >>>>> section of BPF instructions to be uploaded in the kernel.
> >>>>> This step must be done by a "tool". Ophir did it by hacking tc, but
> >>>>> it is not upstreamed yet.
> >>>>> There could be other ways (possibly easier) to achieve the same result.
> >>>>
> >>>> Please change the doc to reflect the tool is not upstreamed yet and the
> >> developer needs to figure out how to extract the data from the binary.
> >>>>
> >>>> I used objdump -j l3_l4 -s tap_bpf_program.o and got a hex dump of
> >>>> the l3_l4 section
> >>>>
> >>>> 0000 bf160000 00000000 61681000 00000000 <Ascii characters> ...
> >>>>
> >>>> Someone schooled in the art of Python coding should be able to
> >>>> convert that output to a ‘C’ data array. :-)
> >>>>
> >>>>>
> >>>>>>> It is a work in progress.
> >>>>>
> >>>>> Contributions are welcome.
> >>>>>
> >>>>>>> This is a very first step to use Linux BPF with DPDK.
> >>>>>>> If there are more interests, we should really streamline its usage
> >>>>>>> for all parts of DPDK which runs on top of some kernel code.
> >>>>>>
> >>>>>> streamlining other parts of DPDK would be nice, but we are now talking
> >> about the tap/eBPF patch.
> >>>>
> >>>> Regards,
> >>>> Keith
> >>
> >> Regards,
> >> Keith
> > 
> 
>