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Date:   Thu, 27 Jan 2022 08:53:04 -0700
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Subject: Re: [PATCH v3 net-next] net: drop_monitor: support drop reason
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To:     menglong8.dong@gmail.com, kuba@kernel.org
Cc:     nhorman@tuxdriver.com, davem@davemloft.net, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, dsahern@kernel.org,
        rostedt@goodmis.org, Menglong Dong <imagedong@tencent.com>,
        Ido Schimmel <idosch@idosch.org>
References: <20220127033356.4050072-1-imagedong@tencent.com>
From:   David Ahern <dsahern@gmail.com>
In-Reply-To: <20220127033356.4050072-1-imagedong@tencent.com>
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On 1/26/22 8:33 PM, menglong8.dong@gmail.com wrote:
> From: Menglong Dong <imagedong@tencent.com>
> 
> In the commit c504e5c2f964 ("net: skb: introduce kfree_skb_reason()")
> drop reason is introduced to the tracepoint of kfree_skb. Therefore,
> drop_monitor is able to report the drop reason to users by netlink.
> 
> For now, the number of drop reason is passed to users ( seems it's
> a little troublesome to pass the drop reason as string ). Therefore,
> users can do some customized description of the reason.
> 
> Signed-off-by: Menglong Dong <imagedong@tencent.com>
> ---
> v3:
> - referring to cb->reason and cb->pc directly in
>   net_dm_packet_report_fill()
> 
> v2:
> - get a pointer to struct net_dm_skb_cb instead of local var for
>   each field
> ---
>  include/uapi/linux/net_dropmon.h |  1 +
>  net/core/drop_monitor.c          | 16 ++++++++++++----
>  2 files changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/include/uapi/linux/net_dropmon.h b/include/uapi/linux/net_dropmon.h
> index 66048cc5d7b3..b2815166dbc2 100644
> --- a/include/uapi/linux/net_dropmon.h
> +++ b/include/uapi/linux/net_dropmon.h
> @@ -93,6 +93,7 @@ enum net_dm_attr {
>  	NET_DM_ATTR_SW_DROPS,			/* flag */
>  	NET_DM_ATTR_HW_DROPS,			/* flag */
>  	NET_DM_ATTR_FLOW_ACTION_COOKIE,		/* binary */
> +	NET_DM_ATTR_REASON,			/* u32 */
>  

For userspace to properly convert reason from id to string, enum
skb_drop_reason needs to be moved from skbuff.h to a uapi file.
include/uapi/linux/net_dropmon.h seems like the best candidate to me.
Maybe others have a better idea.