On 10/27/22 1:00 PM, Stanislav Fomichev wrote:
Example on how the metadata is prepared from the BPF context
and consumed by AF_XDP:
- bpf_xdp_metadata_have_rx_timestamp to test whether it's supported;
if not, I'm assuming verifier will remove this "if (0)" branch
- bpf_xdp_metadata_rx_timestamp returns a _copy_ of metadata;
the program has to bpf_xdp_adjust_meta+memcpy it;
maybe returning a pointer is better?
- af_xdp consumer grabs it from data-<expected_metadata_offset> and
makes sure timestamp is not empty
- when loading the program, we pass BPF_F_XDP_HAS_METADATA+prog_ifindex
Cc: Martin KaFai Lau <martin.lau@xxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: Willem de Bruijn <willemb@xxxxxxxxxx>
Cc: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Cc: Anatoly Burakov <anatoly.burakov@xxxxxxxxx>
Cc: Alexander Lobakin <alexandr.lobakin@xxxxxxxxx>
Cc: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
Cc: Maryam Tahhan <mtahhan@xxxxxxxxxx>
Cc: xdp-hints@xxxxxxxxxxxxxxx
Cc: netdev@xxxxxxxxxxxxxxx
Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
---
.../testing/selftests/bpf/progs/xskxceiver.c | 22 ++++++++++++++++++
tools/testing/selftests/bpf/xskxceiver.c | 23 ++++++++++++++++++-
2 files changed, 44 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/bpf/progs/xskxceiver.c b/tools/testing/selftests/bpf/progs/xskxceiver.c
index b135daddad3a..83c879aa3581 100644
--- a/tools/testing/selftests/bpf/progs/xskxceiver.c
+++ b/tools/testing/selftests/bpf/progs/xskxceiver.c
@@ -12,9 +12,31 @@ struct {
__type(value, __u32);
} xsk SEC(".maps");
+extern int bpf_xdp_metadata_have_rx_timestamp(struct xdp_md *ctx) __ksym;
+extern __u32 bpf_xdp_metadata_rx_timestamp(struct xdp_md *ctx) __ksym;
+
SEC("xdp")
int rx(struct xdp_md *ctx)
{
+ void *data, *data_meta;
+ __u32 rx_timestamp;
+ int ret;
+
+ if (bpf_xdp_metadata_have_rx_timestamp(ctx)) {
+ ret = bpf_xdp_adjust_meta(ctx, -(int)sizeof(__u32));
+ if (ret != 0)
+ return XDP_DROP;
+
+ data = (void *)(long)ctx->data;
+ data_meta = (void *)(long)ctx->data_meta;
+
+ if (data_meta + sizeof(__u32) > data)
+ return XDP_DROP;
+
+ rx_timestamp = bpf_xdp_metadata_rx_timestamp(ctx);
+ __builtin_memcpy(data_meta, &rx_timestamp, sizeof(__u32));
+ }
Thanks for the patches. I took a quick look at patch 1 and 2 but haven't had a
chance to look at the implementation details (eg. KF_UNROLL...etc), yet.
Overall (with the example here) looks promising. There is a lot of flexibility
on whether the xdp prog needs any hint at all, which hint it needs, and how to
store it.
+
return bpf_redirect_map(&xsk, ctx->rx_queue_index, XDP_PASS);
}
diff --git a/tools/testing/selftests/bpf/xskxceiver.c b/tools/testing/selftests/bpf/xskxceiver.c
index 066bd691db13..ce82c89a432e 100644
--- a/tools/testing/selftests/bpf/xskxceiver.c
+++ b/tools/testing/selftests/bpf/xskxceiver.c
@@ -871,7 +871,9 @@ static bool is_offset_correct(struct xsk_umem_info *umem, struct pkt_stream *pkt
static bool is_pkt_valid(struct pkt *pkt, void *buffer, u64 addr, u32 len)
{
void *data = xsk_umem__get_data(buffer, addr);
+ void *data_meta = data - sizeof(__u32);
struct iphdr *iphdr = (struct iphdr *)(data + sizeof(struct ethhdr));
+ __u32 rx_timestamp = 0;
if (!pkt) {
ksft_print_msg("[%s] too many packets received\n", __func__);
@@ -907,6 +909,13 @@ static bool is_pkt_valid(struct pkt *pkt, void *buffer, u64 addr, u32 len)
return false;
}
+ memcpy(&rx_timestamp, data_meta, sizeof(rx_timestamp));
+ if (rx_timestamp == 0) {
+ ksft_print_msg("Invalid metadata received: ");
+ ksft_print_msg("got %08x, expected != 0\n", rx_timestamp);
+ return false;
+ }
+
return true;
}
