Re: Headers for whitelisted kernel functions available to BPF programs

[Kenny Ho <y2kenny@gmail.com>]

On Fri, Jun 4, 2021 at 4:47 PM Kenny Ho <y2kenny@gmail.com> wrote:
>
> On Fri, Jun 4, 2021 at 12:11 PM Yonghong Song <yhs@fb.com> wrote:
> > On 6/3/21 11:13 PM, Martin KaFai Lau wrote:
> > >
> > > Making the kfunc call whitelist more accessible is useful in general.
> > > The bpf tcp-cc struct_ops is the only prog type supporting kfunc call.
> > > What is your use case to introspect this whitelist?
> >
> > Agree. It would be good if you can share your use case.
>
> At the high level, I am trying to see if we can use bpf in the drm
> subsystem and gpu drivers which are kernel modules.  My initial
> motivation was to use bpf for dynamic/run-time reconfiguration of the
> drm/gpu driver (for experimentation.)  But now that I learned more
> about bpf, I think there are quite a few more things I can do with it.
> (Debugging during GPU hw bring-ups, profiling driver performance in
> live system, etc.)  I have been looking into bpf with kprobe and
> struct_ops.
>
> In terms of kernel module support for bpf/btf, Andrii told me about it
> last year and I see that his feature is in (I was able to do a btf
> dump file for /sys/kernel/btf/amdgpu, /sys/kernel/btf/drm_ttm_helper,
> for example.)  The next thing I thought about was having helper
> functions from kernel modules and Toke pointed me to Martin's patch
> around "unstable helpers"/calling whitelisted kernel functions and
> this is where we are at.

Yonghong and Martin, does the use case make sense?  Or am I trying to
do something stupid?

Kenny