[PATCH v7 bpf-next 10/14] bpf: add new frame_length field to the XDP ctx

From: Lorenzo Bianconi <lorenzo@kernel.org>
Date: 2021-03-19 21:49:17
Also in: bpf
Subsystem: bpf [core], bpf [general] (safe dynamic programs and tools), bpf [networking] (tcx & tc bpf, sock_addr), networking [general], the rest, xdp (express data path) · Maintainers: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Martin KaFai Lau, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds, David S. Miller, Jesper Dangaard Brouer, John Fastabend

From: Eelco Chaudron <echaudro@redhat.com>

This patch adds a new field to the XDP context called frame_length,
which will hold the full length of the packet, including fragments
if existing.

eBPF programs can determine if fragments are present using something
like:

  if (ctx->data_end - ctx->data < ctx->frame_length) {
    /* Fragements exists. /*
  }

Signed-off-by: Eelco Chaudron <echaudro@redhat.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 include/linux/filter.h         |  7 +++++++
 include/net/xdp.h              | 12 ++++++++++++
 include/uapi/linux/bpf.h       |  1 +
 net/core/filter.c              |  8 ++++++++
 net/core/xdp.c                 |  1 +
 tools/include/uapi/linux/bpf.h |  1 +
 6 files changed, 30 insertions(+)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index b2b85b2cad8e..511d812fd18c 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h

@@ -768,6 +768,13 @@ static __always_inline u32 bpf_prog_run_xdp(const struct bpf_prog *prog,
 	 * already takes rcu_read_lock() when fetching the program, so
 	 * it's not necessary here anymore.
 	 */
+	xdp->frame_length = xdp->data_end - xdp->data;
+	if (unlikely(xdp->mb)) {
+		struct xdp_shared_info *xdp_sinfo;
+
+		xdp_sinfo = xdp_get_shared_info_from_buff(xdp);
+		xdp->frame_length += xdp_sinfo->data_length;
+	}
 	return __BPF_PROG_RUN(prog, xdp, BPF_DISPATCHER_FUNC(xdp));
 }

diff --git a/include/net/xdp.h b/include/net/xdp.h
index 19cd6642e087..e47d9e8da547 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h

@@ -75,6 +75,10 @@ struct xdp_buff {
 	struct xdp_txq_info *txq;
 	u32 frame_sz:31; /* frame size to deduce data_hard_end/reserved tailroom*/
 	u32 mb:1; /* xdp non-linear buffer */
+	u32 frame_length; /* Total frame length across all buffers. Only needs
+			   * to be updated by helper functions, as it will be
+			   * initialized at XDP program start.
+			   */
 };
 
 static __always_inline void

@@ -235,6 +239,14 @@ void xdp_convert_frame_to_buff(struct xdp_frame *frame, struct xdp_buff *xdp)
 	xdp->data_meta = frame->data - frame->metasize;
 	xdp->frame_sz = frame->frame_sz;
 	xdp->mb = frame->mb;
+	xdp->frame_length = frame->len;
+
+	if (unlikely(xdp->mb)) {
+		struct xdp_shared_info *xdp_sinfo;
+
+		xdp_sinfo = xdp_get_shared_info_from_buff(xdp);
+		xdp->frame_length += xdp_sinfo->data_length;
+	}
 }
 
 static inline

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 2d3036e292a9..4dcc5ad736b4 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h

@@ -5213,6 +5213,7 @@ struct xdp_md {
 	__u32 rx_queue_index;  /* rxq->queue_index  */
 
 	__u32 egress_ifindex;  /* txq->dev->ifindex */
+	__u32 frame_length;
 };
 
 /* DEVMAP map-value layout

diff --git a/net/core/filter.c b/net/core/filter.c
index a607ea8321bd..b047757bd839 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c

@@ -3873,6 +3873,7 @@ static int bpf_xdp_mb_adjust_tail(struct xdp_buff *xdp, int offset)
 		memset(xdp_get_frag_address(frag) + size, 0, offset);
 		xdp_set_frag_size(frag, size + offset);
 		xdp_sinfo->data_length += offset;
+		xdp->frame_length += offset;
 	} else {
 		int i, frags_to_free = 0;

@@ -3894,6 +3895,7 @@ static int bpf_xdp_mb_adjust_tail(struct xdp_buff *xdp, int offset)
 				 * to adjust the data_length in line.
 				 */
 				xdp_sinfo->data_length -= shrink;
+				xdp->frame_length -= shrink;
 				xdp_set_frag_size(frag, size - shrink);
 				break;
 			}

@@ -9126,6 +9128,12 @@ static u32 xdp_convert_ctx_access(enum bpf_access_type type,
 		*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->dst_reg,
 				      offsetof(struct net_device, ifindex));
 		break;
+	case offsetof(struct xdp_md, frame_length):
+		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct xdp_buff,
+						       frame_length),
+				      si->dst_reg, si->src_reg,
+				      offsetof(struct xdp_buff, frame_length));
+		break;
 	}
 
 	return insn - insn_buf;

diff --git a/net/core/xdp.c b/net/core/xdp.c
index 7388bc6d680b..fb7d0724a5b6 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c

@@ -510,6 +510,7 @@ void xdp_return_num_frags_from_buff(struct xdp_buff *xdp, u16 num_frags)
 		struct page *page = xdp_get_frag_page(frag);
 
 		xdp_sinfo->data_length -= xdp_get_frag_size(frag);
+		xdp->frame_length -= xdp_get_frag_size(frag);
 		__xdp_return(page_address(page), &xdp->rxq->mem, false, NULL);
 	}
 	xdp_sinfo->nr_frags -= num_frags;

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 2d3036e292a9..4dcc5ad736b4 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h

@@ -5213,6 +5213,7 @@ struct xdp_md {
 	__u32 rx_queue_index;  /* rxq->queue_index  */
 
 	__u32 egress_ifindex;  /* txq->dev->ifindex */
+	__u32 frame_length;
 };
 
 /* DEVMAP map-value layout

-- 
2.30.2

`h`	back out one level
`j`	next message in thread
`k`	previous message in thread
`l`	drill in
`Esc`	close help / fold thread tree
`?`	toggle this help