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

[Lorenzo Bianconi]

From: Eelco Chaudron <echau...@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 <echau...@redhat.com>
Signed-off-by: Lorenzo Bianconi <lore...@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