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

[Thomas Monjalon]

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?

> > 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.

> > 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.