Re: [PATCH] tap: fix build of tap_bpf_program

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 19 Jul 2023 11:03:36 +0100
Ferruh Yigit <ferruh.yigit@amd.com> wrote:

> On 7/19/2023 11:00 AM, Ferruh Yigit wrote:
> > On 7/17/2023 8:15 PM, Stephen Hemminger wrote:  
> >> The tap_bpf_program.c is not built as part of normal DPDK
> >> EAL environment. It is intended to be built standalone
> >> and does not use rte_common.h.
> >>
> >> This reverts the related change from
> >> commit ef5baf3486e0 ("replace packed attributes")
> >>
> >> Note: this patch will cause expected warnings from checkpatch
> >> because the code involved is not used directly in DPDK environment.
> >>
> >> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> >>  
> > 
> > Agree, this seems done by mistake as part of batch update,
> > 
> > Acked-by: Ferruh Yigit <ferruh.yigit@amd.com>
> > 
> > 
> > But I can't update the bpf file at all, if I am not missing something I  
> 
> * I can't *compile* the bpf file ...
> 
> > am not sure if we should get just this update or have a patch/patchset
> > that fixes the build.
> > 
> > @Ophir, how the bpf file is compiled? And did you test it recently?
> > 
> > I am using command from the documentation:
> > `clang -O2 -emit-llvm -c tap_bpf_program.c -o - | llc -march=bpf
> > -filetype=obj -o tap_bpf_program.o`

It looks like this won't work because it was expecting to be able
to find header files from older version of iproute2.  These are not
distributed, and the change to support libbpf in iproute2 makes the
current versions not work.

As a stopgap, will look back in history and see what version of header
files will at least get a working build.

From there, need to replace how the conversion of .o to array works.
Would prefer to use dlopen() to read the ELF file rather than expecting
developers to hack together their own tools.

Not sure how much effort is really needed here. This is only being
used for the case of rte_flow with multiq RSS. Probably, no one ever
used it.