Re: [RFC PATCH bpf-next v1 0/3] bpf: Add BPF program type for overriding tracepoint probes

[Steven Rostedt <rostedt@goodmis.org>]

On Wed, 17 Sep 2025 15:22:39 +0800
Fuyu Zhao <zhaofuyu@vivo.com> wrote:

> Hi everyone,
> 
> This patchset introduces a new BPF program type that allows overriding
> a tracepoint probe function registered via register_trace_*.
> 
> Motivation
> ----------
> Tracepoint probe functions registered via register_trace_* in the kernel
> cannot be dynamically modified, changing a probe function requires recompiling
> the kernel and rebooting. Nor can BPF programs change an existing
> probe function.

I'm confused by what you mean by "tracepoint probe function"?

You mean the function callback that gets called via the "register_trace_*()"?

> 
> Overiding tracepoint supports a way to apply patches into kernel quickly
> (such as applying security ones), through predefined static tracepoints,
> without waiting for upstream integration.

This sounds way out of scope for tracepoints. Please provide a solid
example for this.

> 
> This patchset demonstrates the way to override probe functions by BPF program.
> 
> Overview
> --------
> This patchset adds BPF_PROG_TYPE_RAW_TRACEPOINT_OVERRIDE program type.
> When this type of BPF program attaches, it overrides the target tracepoint
> probe function.
> 
> And it also extends a new struct type "tracepoint_func_snapshot", which extends
> the tracepoint structure. It is used to record the original probe function
> registered by kernel after BPF program being attached and restore from it
> after detachment. 

The tracepoint structure exists for every tracepoint in the kernel. By
adding a pointer to it, you just increased the size of the tracepoint. I'm
already complaining that each tracepoint causes around 5K of memory
overhead, and I'd like to make it smaller.

-- Steve