netdev - Re: [PATCH net-next v3 2/4] net: tap: track dropped skb via kfree_skb

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Date:   Mon, 21 Feb 2022 20:24:12 -0700
From:   David Ahern <dsahern@...il.com>
To:     Dongli Zhang <dongli.zhang@...cle.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        rostedt@...dmis.org, mingo@...hat.com, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, imagedong@...cent.com,
        joao.m.martins@...cle.com, joe.jin@...cle.com, edumazet@...gle.com
Subject: Re: [PATCH net-next v3 2/4] net: tap: track dropped skb via
 kfree_skb_reason()

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@...cle.com>
> Cc: Joe Jin <joe.jin@...cle.com>
> Signed-off-by: Dongli Zhang <dongli.zhang@...cle.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@...nel.org>