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

[Wiles, Keith]

> On Jul 4, 2018, at 3:11 PM, Thomas Monjalon <thomas at monjalon.net> wrote:
> 
> 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.

I agree.

> 
> 
>>>> -----Original Message-----
>>>> From: Wiles, Keith [mailto:keith.wiles at intel.com]
>>>> 
>>>>> On Jun 12, 2018, at 8:44 AM, Thomas Monjalon <thomas at monjalon.net>
>>>> wrote:
>>>>> 
>>>>> 12/06/2018 15:33, Wiles, Keith:
>>>>>> 
>>>>>>> On Jun 12, 2018, at 7:58 AM, Thomas Monjalon
>>>> <thomas at monjalon.net> wrote:
>>>>>>> 
>>>>>>> 12/06/2018 14:36, Wiles, Keith:
>>>>>>>> 
>>>>>>>>> On Jun 12, 2018, at 7:26 AM, Thomas Monjalon
>>>> <thomas at monjalon.net> wrote:
>>>>>>>>> 
>>>>>>>>> 11/06/2018 18:35, Wiles, Keith:
>>>>>>>>>> 
>>>>>>>>>>> On Jun 11, 2018, at 11:06 AM, Ophir Munk
>>>> <ophirmu at 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

Regards,
Keith