Re: [PATCH bpf-next v5 6/7] bpf: Add "live packet" mode for XDP in bpf_prog_run()

Alexei Starovoitov [off-list ref] writes:

On Mon, Jan 03, 2022 at 04:08:11PM +0100, Toke Høiland-Jørgensen wrote:

quoted

+static void xdp_test_run_init_page(struct page *page, void *arg)
+{
+	struct xdp_page_head *head = phys_to_virt(page_to_phys(page));
+	struct xdp_buff *new_ctx, *orig_ctx;
+	u32 headroom = XDP_PACKET_HEADROOM;
+	struct xdp_test_data *xdp = arg;
+	size_t frm_len, meta_len;
+	struct xdp_frame *frm;
+	void *data;
+
+	orig_ctx = xdp->orig_ctx;
+	frm_len = orig_ctx->data_end - orig_ctx->data_meta;
+	meta_len = orig_ctx->data - orig_ctx->data_meta;
+	headroom -= meta_len;
+
+	new_ctx = &head->ctx;
+	frm = &head->frm;
+	data = &head->data;
+	memcpy(data + headroom, orig_ctx->data_meta, frm_len);
+
+	xdp_init_buff(new_ctx, TEST_XDP_FRAME_SIZE, &xdp->rxq);
+	xdp_prepare_buff(new_ctx, data, headroom, frm_len, true);
+	new_ctx->data_meta = new_ctx->data + meta_len;

data vs data_meta is the other way around, no?

Probably needs a selftest to make sure.

Yup, you're right; nice catch! Will fix and add a test for it.

quoted

+static int xdp_recv_frames(struct xdp_frame **frames, int nframes,
+			   struct net_device *dev)
+{
+	gfp_t gfp = __GFP_ZERO | GFP_ATOMIC;
+	void *skbs[TEST_XDP_BATCH];
+	int i, n;
+	LIST_HEAD(list);
+
+	n = kmem_cache_alloc_bulk(skbuff_head_cache, gfp, nframes, skbs);
+	if (unlikely(n == 0)) {
+		for (i = 0; i < nframes; i++)
+			xdp_return_frame(frames[i]);
+		return -ENOMEM;
+	}
+
+	for (i = 0; i < nframes; i++) {
+		struct xdp_frame *xdpf = frames[i];
+		struct sk_buff *skb = skbs[i];
+
+		skb = __xdp_build_skb_from_frame(xdpf, skb, dev);
+		if (!skb) {
+			xdp_return_frame(xdpf);
+			continue;
+		}
+
+		list_add_tail(&skb->list, &list);
+	}
+	netif_receive_skb_list(&list);

Does it need local_bh_disable() like cpumap does?

Yes, I think it probably does, actually. Or at least having it can
potentially improve performance since we're then sure that the whole
batch will be processed at once. Will add!

I've applied patches 1 - 5.

Thanks! Will respin this and the selftest :)