On 03/08/2021 19.10, Kishen Maloor wrote:
diff --git a/samples/bpf/xdpsock_user.c b/samples/bpf/xdpsock_user.c
index 3fd2f6a0d1eb..a0fd3d5414ba 100644
--- a/samples/bpf/xdpsock_user.c
+++ b/samples/bpf/xdpsock_user.c
[...]
@@ -741,6 +745,8 @@ static inline u16 udp_csum(u32 saddr, u32 daddr, u32 len,
#define ETH_FCS_SIZE 4
+#define MD_SIZE (sizeof(struct xdp_user_tx_metadata))
+
#define PKT_HDR_SIZE (sizeof(struct ethhdr) + sizeof(struct iphdr) + \
sizeof(struct udphdr))
@@ -798,8 +804,10 @@ static void gen_eth_hdr_data(void)
static void gen_eth_frame(struct xsk_umem_info *umem, u64 addr)
{
- memcpy(xsk_umem__get_data(umem->buffer, addr), pkt_data,
- PKT_SIZE);
+ if (opt_launch_time)
+ memcpy(xsk_umem__get_data(umem->buffer, addr) + MD_SIZE, pkt_data, PKT_SIZE);
+ else
+ memcpy(xsk_umem__get_data(umem->buffer, addr), pkt_data, PKT_SIZE);
}
I imagined that AF_XDP 'addr' would still point to the start of the
packet data, and that metadata area was access via a negative offset
from 'addr'.
Maybe I misunderstood the code, but it looks like 'addr'
(xsk_umem__get_data(umem->buffer, addr)) points to metadata area, is
this correct?
(and to skip this the code does + MD_SIZE, before memcpy)
One problem/challenge with AF_XDP is that we don't have room in struct
xdp_desc to store info on the size of the metadata area. Bjørn came up
with the idea of having btf_id as last member (access able via minus 4
bytes), as this tells the kernel the size of metadata area.
Maybe you have come up with a better solution?
(of making the metadata area size dynamic)
--Jesper
