Merge branch 'xdp-head-adjustment'

Martin KaFai Lau says:

====================
Allow head adjustment in XDP prog

This series adds a helper to allow head adjusting in XDP prog.  mlx4
driver has been modified to support this feature.  An example is written
to encapsulate a packet with an IPv4/v6 header and then XDP_TX it
out.

v4:
1. Remove XDP_QUERY_FEATURES command.  Instead, check
   the prog->xdp_adjust_head bit inside the driver itself
   during XDP_SETUP_PROG in patch 1of4.
   Thanks for everybody's ideas.
2. Nit changes on sample code per Jesper

v3:
1. Check if the driver supports head adjustment before
   setting the xdp_prog fd to the device in patch 1of4.
2. Remove the page alignment assumption on the data_hard_start.
   Instead, add data_hard_start to the struct xdp_buff and the
   driver has to fill it if it supports head adjustment.
3. Keep the wire MTU as before in mlx4
4. Set map0_byte_count to PAGE_SIZE in patch 3of4

v2:
1. Make a variable name change in bpf_xdp_adjust_head() in patch 1
2. Ensure no less than ETH_HLEN data in bpf_xdp_adjust_head() in patch 1
3. Some clarifications in commit log messages of patch 2 and 3
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 1 deletions

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 6123d9b8e828..0eb0e87dbe9f 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -424,6 +424,12 @@ union bpf_attr {
  *     @len: length of header to be pushed in front
  *     @flags: Flags (unused for now)
  *     Return: 0 on success or negative error
+ *
+ * int bpf_xdp_adjust_head(xdp_md, delta)
+ *     Adjust the xdp_md.data by delta
+ *     @xdp_md: pointer to xdp_md
+ *     @delta: An positive/negative integer to be added to xdp_md.data
+ *     Return: 0 on success or negative on error
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -469,7 +475,8 @@ union bpf_attr {
 	FN(csum_update),		\
 	FN(set_hash_invalid),		\
 	FN(get_numa_node_id),		\
-	FN(skb_change_head),
+	FN(skb_change_head),		\
+	FN(xdp_adjust_head),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call
@@ -576,6 +583,8 @@ struct bpf_sock {
 	__u32 protocol;
 };
 
+#define XDP_PACKET_HEADROOM 256
+
 /* User return codes for XDP prog type.
  * A valid XDP program must return one of these defined values. All other
  * return codes are reserved for future use. Unknown return codes will result