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

[Ihor Solodrai <ihor.solodrai@linux.dev>]

On 6/19/25 10:57 AM, Eduard Zingerman wrote:
> On Thu, 2025-06-19 at 10:55 -0700, Ihor Solodrai wrote:
> 
> [...]
> 
>>> I think Mykyta has kernel/trace/bpf_trace.c:__bpf_dynptr_copy_str() in mind.
>>
>> Thanks for the pointer. So it looks like memset can use
>> bpf_dynptr_slice_rdwr() to handle xdp/skb cases. Something like:
>>
>>       void *ptr = bpf_dynptr_slice_rdwr(&dynptr, 0, buffer, sizeof(buffer));
>>       if (!ptr)
>>           return -EINVAL;
>>
>>       memset(ptr, val, n);
>>
>>       if (ptr == buffer)
>>           bpf_dynptr_write(&dynptr, 0, buffer, sizeof(buffer), 0);
>>
>>
> 
> I think so. In a loop.

But allocating and copying buffers for memset...

It should be possible to walk through fragments like
net/core/filter.c:bpf_xdp_copy_buf does.

Any reasons it's a bad idea?

>