Lorenzo Bianconi [off-list ref] writes:

quoted

Introduce __xdp_build_skb_from_frame and
xdp_build_skb_from_frame
utility routines to build the skb from xdp_frame.
Add xdp multi-buff support to cpumap

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 include/net/xdp.h   |  5 ++++
 kernel/bpf/cpumap.c | 45 +---------------------------
 net/core/xdp.c      | 73
 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 79 insertions(+), 44 deletions(-)

[...]

quoted

diff --git a/net/core/xdp.c b/net/core/xdp.c
index 6c8e743ad03a..55f3e9c69427 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c

@@ -597,3 +597,76 @@ void xdp_warn(const char *msg, const char

*func, const int line)
      WARN(1, "XDP_WARN: %s(line:%d): %s\n", func, line, msg);
 };
 EXPORT_SYMBOL_GPL(xdp_warn);
+
+struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame
*xdpf,
+                                        struct sk_buff *skb,
+                                        struct net_device *dev)
+{
+     unsigned int headroom = sizeof(*xdpf) + xdpf->headroom;
+     void *hard_start = xdpf->data - headroom;
+     skb_frag_t frag_list[MAX_SKB_FRAGS];
+     struct xdp_shared_info *xdp_sinfo;
+     int i, num_frags = 0;
+
+     xdp_sinfo = xdp_get_shared_info_from_frame(xdpf);
+     if (unlikely(xdpf->mb)) {
+             num_frags = xdp_sinfo->nr_frags;
+             memcpy(frag_list, xdp_sinfo->frags,
+                    sizeof(skb_frag_t) * num_frags);
+     }

nit, can you please move the xdp_sinfo assignment inside this 'if'
? This would help to emphasize that regarding xdp_frame tailroom
as xdp_shared_info struct (rather than skb_shared_info) is correct
only when the mb bit is set

thanks,
Shay

ack, will do in v6.

Regards,
Lorenzo

quoted

+
+     skb = build_skb_around(skb, hard_start, xdpf->frame_sz);
+     if (unlikely(!skb))
+             return NULL;

[...]