Re: [PATCH bpf-next v10 1/5] bpf: Add "live packet" mode for XDP in BPF_PROG_RUN

Martin KaFai Lau [off-list ref] writes:

On Tue, Mar 08, 2022 at 03:57:57PM +0100, Toke Høiland-Jørgensen wrote:

quoted

+static int xdp_test_run_batch(struct xdp_test_data *xdp, struct bpf_prog *prog,
+			      u32 repeat)
+{
+	struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
+	int err = 0, act, ret, i, nframes = 0, batch_sz;
+	struct xdp_frame **frames = xdp->frames;
+	struct xdp_page_head *head;
+	struct xdp_frame *frm;
+	bool redirect = false;
+	struct xdp_buff *ctx;
+	struct page *page;
+
+	batch_sz = min_t(u32, repeat, xdp->batch_size);
+
+	local_bh_disable();
+	xdp_set_return_frame_no_direct();
+
+	for (i = 0; i < batch_sz; i++) {
+		page = page_pool_dev_alloc_pages(xdp->pp);
+		if (!page) {
+			err = -ENOMEM;
+			goto out;
+		}
+
+		head = phys_to_virt(page_to_phys(page));
+		reset_ctx(head);
+		ctx = &head->ctx;
+		frm = &head->frm;
+		xdp->frame_cnt++;
+
+		act = bpf_prog_run_xdp(prog, ctx);
+
+		/* if program changed pkt bounds we need to update the xdp_frame */
+		if (unlikely(ctx_was_changed(head))) {
+			ret = xdp_update_frame_from_buff(ctx, frm);
+			if (ret) {
+				xdp_return_buff(ctx);
+				continue;
+			}
+		}
+
+		switch (act) {
+		case XDP_TX:
+			/* we can't do a real XDP_TX since we're not in the
+			 * driver, so turn it into a REDIRECT back to the same
+			 * index
+			 */
+			ri->tgt_index = xdp->dev->ifindex;
+			ri->map_id = INT_MAX;
+			ri->map_type = BPF_MAP_TYPE_UNSPEC;
+			fallthrough;
+		case XDP_REDIRECT:
+			redirect = true;
+			ret = xdp_do_redirect_frame(xdp->dev, ctx, frm, prog);
+			if (ret)
+				xdp_return_buff(ctx);
+			break;
+		case XDP_PASS:
+			frames[nframes++] = frm;
+			break;
+		default:
+			bpf_warn_invalid_xdp_action(NULL, prog, act);
+			fallthrough;
+		case XDP_DROP:
+			xdp_return_buff(ctx);
+			break;
+		}
+	}
+
+out:
+	if (redirect)
+		xdp_do_flush();
+	if (nframes)
+		err = xdp_recv_frames(frames, nframes, xdp->skbs, xdp->dev);

This may overwrite the -ENOMEM with 0.

Argh, oops! And here I thought I was being clever by getting rid of the
indirection through 'ret'. Will fix, thanks!

-Toke