On Fri, 17 Sep 2021 12:02:46 +0200 Lorenzo Bianconi wrote:

quoted

quoted

+static inline unsigned int xdp_get_frag_tailroom(const skb_frag_t *frag)
+{
+	struct page *page = skb_frag_page(frag);
+
+	return page_size(page) - skb_frag_size(frag) - skb_frag_off(frag);
+}  

How do we deal with NICs which can pack multiple skbs into a page frag?
skb_shared_info field to mark the end of last fragment? Just want to make 
sure there is a path to supporting such designs.  

I guess here, intead of using page_size(page) we can rely on xdp_buff->frame_sz
or even on skb_shared_info()->xdp_frag_truesize (assuming all fragments from a
given hw have the same truesize, but I think this is something we can rely on)

static inline unsigned int xdp_get_frag_tailroom(struct xdp_buff *xdp,
						 const skb_frag_t *frag)
{
	return xdp->frame_sz - skb_frag_size(frag) - skb_frag_off(frag);
}

what do you think?

Could work! We'd need to document the semantics of frame_sz for mb
frames clearly but I don't see why not.