The code which builds an skb from an &xdp_buff keeps multiplying itself
around the drivers with almost no changes. Let's try to stop that by
adding a generic function.
There's __xdp_build_skb_from_frame() already, so just convert it to take
&xdp_buff instead, while making the original one a wrapper. The original
one always took an already allocated skb, allow both variants here -- if
no skb passed, which is expected when calling from a driver, pick one via
napi_build_skb().

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
---
 include/net/xdp.h |  1 +
 net/core/xdp.c    | 55 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/include/net/xdp.h b/include/net/xdp.h
index ae92af8b782d..fa56570b15d7 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -330,6 +330,7 @@ xdp_update_skb_shared_info(struct sk_buff *skb, u8 nr_frags,
 void xdp_warn(const char *msg, const char *func, const int line);
 #define XDP_WARN(msg) xdp_warn(msg, __func__, __LINE__)
 
+struct sk_buff *xdp_build_skb_from_buff(const struct xdp_buff *xdp);
 struct xdp_frame *xdp_convert_zc_to_xdp_frame(struct xdp_buff *xdp);
 struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame *xdpf,
 					   struct sk_buff *skb,
diff --git a/net/core/xdp.c b/net/core/xdp.c
index 63f4f418e4e1..e5395048a925 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -614,6 +614,61 @@ void xdp_warn(const char *msg, const char *func, const int line)
 };
 EXPORT_SYMBOL_GPL(xdp_warn);
 
+/**
+ * xdp_build_skb_from_buff - create an skb from an &xdp_buff
+ * @xdp: &xdp_buff to convert to an skb
+ *
+ * Perform common operations to create a new skb to pass up the stack from
+ * an &xdp_buff: allocate an skb head from the NAPI percpu cache, initialize
+ * skb data pointers and offsets, set the recycle bit if the buff is PP-backed,
+ * Rx queue index, protocol and update frags info.
+ *
+ * Return: new &sk_buff on success, %NULL on error.
+ */
+struct sk_buff *xdp_build_skb_from_buff(const struct xdp_buff *xdp)
+{
+	const struct xdp_rxq_info *rxq = xdp->rxq;
+	const struct skb_shared_info *sinfo;
+	struct sk_buff *skb;
+	u32 nr_frags = 0;
+	int metalen;
+
+	if (unlikely(xdp_buff_has_frags(xdp))) {
+		sinfo = xdp_get_shared_info_from_buff(xdp);
+		nr_frags = sinfo->nr_frags;
+	}
+
+	skb = napi_build_skb(xdp->data_hard_start, xdp->frame_sz);
+	if (unlikely(!skb))
+		return NULL;
+
+	skb_reserve(skb, xdp->data - xdp->data_hard_start);
+	__skb_put(skb, xdp->data_end - xdp->data);
+
+	metalen = xdp->data - xdp->data_meta;
+	if (metalen > 0)
+		skb_metadata_set(skb, metalen);
+
+	if (is_page_pool_compiled_in() && rxq->mem.type == MEM_TYPE_PAGE_POOL)
+		skb_mark_for_recycle(skb);
+
+	skb_record_rx_queue(skb, rxq->queue_index);
+
+	if (unlikely(nr_frags)) {
+		u32 ts;
+
+		ts = sinfo->xdp_frags_truesize ? : nr_frags * xdp->frame_sz;
+		xdp_update_skb_shared_info(skb, nr_frags,
+					   sinfo->xdp_frags_size, ts,
+					   xdp_buff_is_frag_pfmemalloc(xdp));
+	}
+
+	skb->protocol = eth_type_trans(skb, rxq->dev);
+
+	return skb;
+}
+EXPORT_SYMBOL_GPL(xdp_build_skb_from_buff);
+
 struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame *xdpf,
 					   struct sk_buff *skb,
 					   struct net_device *dev)
-- 
2.46.2