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

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Date:   Mon, 21 Feb 2022 20:31:48 -0800
From:   Dongli Zhang <dongli.zhang@...cle.com>
To:     David Ahern <dsahern@...il.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()

Hi David,

On 2/21/22 7:24 PM, David Ahern wrote:
> 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>
> 

I will re-order the reasons in the same patch and re-send with your Reviewed-by
in the next version.

Thank you very much!

Dongli Zhang