On 2/19/22 12:12 PM, Dongli Zhang wrote:
> The TAP can be used as vhost-net backend. E.g., the tap_handle_frame() is
> the interface to forward the skb from TAP to vhost-net/virtio-net.
>
> However, there are many "goto drop" in the TAP driver. Therefore, the
> kfree_skb_reason() is involved at each "goto drop" to help userspace
> ftrace/ebpf to track the reason for the loss of packets.
>
> The below reasons are introduced:
>
> - SKB_DROP_REASON_SKB_CSUM
> - SKB_DROP_REASON_SKB_COPY_DATA
> - SKB_DROP_REASON_SKB_GSO_SEG
> - SKB_DROP_REASON_DEV_HDR
> - SKB_DROP_REASON_FULL_RING
>
> Cc: Joao Martins <joao.m.martins@xxxxxxxxxx>
> Cc: Joe Jin <joe.jin@xxxxxxxxxx>
> Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
> ---
> drivers/net/tap.c | 30 ++++++++++++++++++++++--------
> include/linux/skbuff.h | 9 +++++++++
> include/trace/events/skb.h | 5 +++++
> 3 files changed, 36 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/net/tap.c b/drivers/net/tap.c
> index 8e3a28ba6b28..ab3592506ef8 100644
> --- a/drivers/net/tap.c
> +++ b/drivers/net/tap.c
> @@ -322,6 +322,7 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb)
> struct tap_dev *tap;
> struct tap_queue *q;
> netdev_features_t features = TAP_FEATURES;
> + int drop_reason;
enum skb_drop_reason drop_reason;
>
> tap = tap_dev_get_rcu(dev);
> if (!tap)
> @@ -343,12 +344,16 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb)
> struct sk_buff *segs = __skb_gso_segment(skb, features, false);
> struct sk_buff *next;
>
> - if (IS_ERR(segs))
> + if (IS_ERR(segs)) {
> + drop_reason = SKB_DROP_REASON_SKB_GSO_SEG;
> goto drop;
> + }
>
> if (!segs) {
> - if (ptr_ring_produce(&q->ring, skb))
> + if (ptr_ring_produce(&q->ring, skb)) {
> + drop_reason = SKB_DROP_REASON_FULL_RING;
> goto drop;
> + }
> goto wake_up;
> }
you missed the walk of segs and calling ptr_ring_produce.
>
