Re: [PATCH net-next v1 1/2] net: introduce and use skb_frag_fill_page_desc()

[Simon Horman <simon.horman@corigine.com>]

On Wed, May 10, 2023 at 08:07:36PM +0800, Yunsheng Lin wrote:
> On 2023/5/10 16:40, Simon Horman wrote:
> > + XDP people and ML
> > 
> > On Tue, May 09, 2023 at 07:41:45PM +0800, Yunsheng Lin wrote:
> >> Most users use __skb_frag_set_page()/skb_frag_off_set()/
> >> skb_frag_size_set() to fill the page desc for a skb frag.
> >>
> >> Introduce skb_frag_fill_page_desc() to do that.
> >>
> >> net/bpf/test_run.c does not call skb_frag_off_set() to
> >> set the offset, "copy_from_user(page_address(page), ...)"
> >> suggest that it is assuming offset to be initialized as
> >> zero, so call skb_frag_fill_page_desc() with offset being
> >> zero for this case.
> > 
> > I think the question is, what is the value of bv_offset before this patch.
> 
> sinfo seems to be part of the 'data' kzalloced in
> bpf_test_init(), so bv_offset should be zero too.

Thanks, that sounds logical to me.

> > Lorenzo and Stanislav, do you have any insight here?
> > 
> >>
> >> Also, skb_frag_set_page() is not used anymore, so remove
> >> it.
> >>
> >> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
> > 
> > ...
> > 
> >> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> >> index 738776ab8838..30be21c7d05f 100644
> >> --- a/include/linux/skbuff.h
> >> +++ b/include/linux/skbuff.h
> >> @@ -2411,6 +2411,15 @@ static inline unsigned int skb_pagelen(const struct sk_buff *skb)
> >>  	return skb_headlen(skb) + __skb_pagelen(skb);
> >>  }
> >>  
> >> +static inline void skb_frag_fill_page_desc(skb_frag_t *frag,
> >> +					   struct page *page,
> >> +					   int off, int size)
> >> +{
> >> +	frag->bv_page = page;
> >> +	frag->bv_offset = off;
> > 
> > Maybe it is slightly nicer to use skb_frag_off_set() here.
> 
> Yes, that is good idea.
> But we need to move the definition of skb_frag_off_set() before
> skb_frag_fill_page_desc in order to use it, I try to keep the
> patch simple for reviewing for now, so I perfer to not do it
> now if that is ok for you.

Sure, that is fine by me.