[RFC PATCH bpf-next 0/7] bpf: Implement BPF_LINK_UPDATE for tracing links

[Jordan Rife]

On Fri, Nov 21, 2025 at 05:43:28PM -0800, Alexei Starovoitov wrote:
> On Mon, Nov 17, 2025 at 4:53 PM Jordan Rife <jordan at jrife.io> wrote:
> >
> > Implement update_prog for bpf_tracing_link_lops to enable
> > BPF_LINK_UPDATE for fentry, fexit, fmod_ret, freplace, etc. links.
> >
> > My initial motivation for this was to enable a use case where one
> > process creates and owns links pointing to "hooks" within a tc, xdp, ...
> > attachment and an external "plugin" loads freplace programs and updates
> > links to these hooks. Aside from that though, it seemed like it could
> > be useful to be able to atomically swap out the program associated with
> > an freplace/fentry/fexit/fmod_ret link more generally.
> 
> I don't think we should burden the kernel with link_update for fentry/fexit.
> bpf trampoline is already complex enough. I don't feel that
> additional complexity is justified.

OK. I could drop fentry/fexit from the series to avoid complexity with
the associated arch-specific stuff.

Jordan