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Date:   Mon, 21 Feb 2022 20:24:12 -0700
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Subject: Re: [PATCH net-next v3 2/4] net: tap: track dropped skb via
 kfree_skb_reason()
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To:     Dongli Zhang <dongli.zhang@oracle.com>, netdev@vger.kernel.org,
        bpf@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, davem@davemloft.net, kuba@kernel.org,
        rostedt@goodmis.org, mingo@redhat.com, ast@kernel.org,
        daniel@iogearbox.net, andrii@kernel.org, imagedong@tencent.com,
        joao.m.martins@oracle.com, joe.jin@oracle.com, edumazet@google.com
References: <20220221053440.7320-1-dongli.zhang@oracle.com>
 <20220221053440.7320-3-dongli.zhang@oracle.com>
From:   David Ahern <dsahern@gmail.com>
In-Reply-To: <20220221053440.7320-3-dongli.zhang@oracle.com>
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Precedence: bulk

On 2/20/22 10:34 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@oracle.com>
> Cc: Joe Jin <joe.jin@oracle.com>
> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> ---
> Changed since v1:
>   - revise the reason name
> Changed since v2:
>   - declare drop_reason as type "enum skb_drop_reason"
>   - handle the drop in skb_list_walk_safe() case
> 
>  drivers/net/tap.c          | 35 +++++++++++++++++++++++++----------
>  include/linux/skbuff.h     |  9 +++++++++
>  include/trace/events/skb.h |  5 +++++
>  3 files changed, 39 insertions(+), 10 deletions(-)
> 

couple of places where the new reason should be in reverse xmas order;
logic wise:

Reviewed-by: David Ahern <dsahern@kernel.org>