Re: [PATCH bpf-next 1/2] bpf: add bpf_dynptr_memset() kfunc

[Eduard Zingerman <eddyz87@gmail.com>]

On Mon, 2025-06-23 at 14:38 -0700, Andrii Nakryiko wrote:
> On Thu, Jun 19, 2025 at 11:17 AM Eduard Zingerman <eddyz87@gmail.com> wrote:
> > 
> > On Thu, 2025-06-19 at 11:13 -0700, Eduard Zingerman wrote:
> > 
> > [...]
> > 
> > > Also, what's the plan if you'd like to memset only a fragment of the
> > > memory pointed-to by dynptr?
> > 
> > Oh, I see, there is bpf_dynptr_adjust(), sorry for the noise.
> > 
> 
> Even though we do have bpf_dynptr_adjust() for maximum generality and
> flexibility, for most dynptr-based APIs we try to pass also additional
> offset into dynptr to avoid unnecessary overhead. So it's not a bad
> idea to add this to bpf_memset(), IMO.
> 
> bpf_memset(struct bpf_dynptr *dptr, u32 off, u8 val, u32 n) ?
> 
> a bit unfortunate that we have 3 integers that you need to be careful
> to not swap accidentally, but even with just val and n you'd have to
> be careful. For other APIs we normally have offset to follow dynptr
> pointer, so hopefully this arrangement won't that surprising.
> 
> Thoughts?

Unfortunate indeed.
The off and n being separated looks weird, tbh.
For dynptr funcs we actually have "dptr, off, size" everywhere, maybe
do the same here?