On 11/14/22 7:02 PM, Stanislav Fomichev wrote:
Implement new bpf_xdp_metadata_export_to_skb kfunc which
prepares compatible xdp metadata for kernel consumption.
This kfunc should be called prior to bpf_redirect
or when XDP_PASS'ing the frame into the kernel (note, the drivers
have to be updated to enable consuming XDP_PASS'ed metadata).
veth driver is amended to consume this metadata when converting to skb.
Internally, XDP_FLAGS_HAS_SKB_METADATA flag is used to indicate
whether the frame has skb metadata. The metadata is currently
stored prior to xdp->data_meta. bpf_xdp_adjust_meta refuses
to work after a call to bpf_xdp_metadata_export_to_skb (can lift
this requirement later on if needed, we'd have to memmove
xdp_skb_metadata).
It is ok to refuse bpf_xdp_adjust_meta() after bpf_xdp_metadata_export_to_skb()
for now. However, it will also need to refuse bpf_xdp_adjust_head().
[ ... ]
+/* For the packets directed to the kernel, this kfunc exports XDP metadata
+ * into skb context.
+ */
+noinline int bpf_xdp_metadata_export_to_skb(const struct xdp_md *ctx)
+{
+ return 0;
+}
+
I think it is still better to return 'struct xdp_skb_metata *' instead of
true/false. Like:
noinline struct xdp_skb_metata *bpf_xdp_metadata_export_to_skb(const struct
xdp_md *ctx)
{
return 0;
}
The KF_RET_NULL has already been set in
BTF_SET8_START_GLOBAL(xdp_metadata_kfunc_ids). There is
"xdp_btf_struct_access()" that can allow write access to 'struct xdp_skb_metata'
What else is missing? We can try to solve it.
Then there is no need for this double check in patch 8 selftest which is not
easy to use:
+ if (bpf_xdp_metadata_export_to_skb(ctx) < 0) {
+ bpf_printk("bpf_xdp_metadata_export_to_skb failed");
+ return XDP_DROP;
+ }
[ ... ]
+ skb_metadata = ctx->skb_metadata;
+ if (!skb_metadata) {
+ bpf_printk("no ctx->skb_metadata");
+ return XDP_DROP;
+ }
[ ... ]
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index b444b1118c4f..71e3bc7ad839 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -6116,6 +6116,12 @@ enum xdp_action {
XDP_REDIRECT,
};
+/* Subset of XDP metadata exported to skb context.
+ */
+struct xdp_skb_metadata {
+ __u64 rx_timestamp;
+};
+
/* user accessible metadata for XDP packet hook
* new fields must be added to the end of this structure
*/
@@ -6128,6 +6134,7 @@ struct xdp_md {
__u32 rx_queue_index; /* rxq->queue_index */
__u32 egress_ifindex; /* txq->dev->ifindex */
+ __bpf_md_ptr(struct xdp_skb_metadata *, skb_metadata);
Once the above bpf_xdp_metadata_export_to_skb() returning a pointer works, then
it can be another kfunc 'struct xdp_skb_metata * bpf_xdp_get_skb_metadata(const
struct xdp_md *ctx)' to return the skb_metadata which was a similar point
discussed in the previous RFC.
