netdev - Re: [PATCH net-next v4 4/4] net: tun: track dropped skb via kfree_skb

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Date:   Sun, 27 Feb 2022 18:20:23 -0700
From:   David Ahern <dsahern@...nel.org>
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 v4 4/4] net: tun: track dropped skb via
 kfree_skb_reason()

On 2/26/22 1:49 AM, Dongli Zhang wrote:
> The TUN can be used as vhost-net backend. E.g, the tun_net_xmit() is the
> interface to forward the skb from TUN to vhost-net/virtio-net.
> 
> However, there are many "goto drop" in the TUN 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_PULL
> - SKB_DROP_REASON_SKB_TRIM
> - SKB_DROP_REASON_DEV_READY
> - SKB_DROP_REASON_TAP_FILTER
> - SKB_DROP_REASON_TAP_TXFILTER
> 
> 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"
> Changed since v3:
>   - rename to TAP_FILTER and TAP_TXFILTER
>   - honor reverse xmas tree style declaration for 'drop_reason' in
>     tun_net_xmit()
> 
>  drivers/net/tun.c          | 37 ++++++++++++++++++++++++++++---------
>  include/linux/skbuff.h     | 10 ++++++++++
>  include/trace/events/skb.h |  5 +++++
>  3 files changed, 43 insertions(+), 9 deletions(-)
> 

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