netdev - Re: [PATCH v6 net-next] net: drop_monitor: support drop reason

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Date:   Sun, 6 Feb 2022 13:26:41 +0200
From:   Ido Schimmel <idosch@...sch.org>
To:     menglong8.dong@...il.com
Cc:     kuba@...nel.org, dsahern@...nel.org, nhorman@...driver.com,
        davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, rostedt@...dmis.org,
        Menglong Dong <imagedong@...cent.com>
Subject: Re: [PATCH v6 net-next] net: drop_monitor: support drop reason

On Sat, Feb 05, 2022 at 04:17:38PM +0800, menglong8.dong@...il.com wrote:
> diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
> index 7b288a121a41..1180f1a28599 100644
> --- a/net/core/drop_monitor.c
> +++ b/net/core/drop_monitor.c
> @@ -48,6 +48,16 @@
>  static int trace_state = TRACE_OFF;
>  static bool monitor_hw;
>  
> +#undef EM
> +#undef EMe
> +
> +#define EM(a, b)	[a] = #b,
> +#define EMe(a, b)	[a] = #b
> +
> +static const char *drop_reasons[SKB_DROP_REASON_MAX + 1] = {
> +	TRACE_SKB_DROP_REASON
> +};
> +
>  /* net_dm_mutex
>   *
>   * An overall lock guarding every operation coming from userspace.
> @@ -126,6 +136,7 @@ struct net_dm_skb_cb {
>  		struct devlink_trap_metadata *hw_metadata;
>  		void *pc;
>  	};
> +	enum skb_drop_reason reason;
>  };
>  
>  #define NET_DM_SKB_CB(__skb) ((struct net_dm_skb_cb *)&((__skb)->cb[0]))
> @@ -498,6 +509,7 @@ static void net_dm_packet_trace_kfree_skb_hit(void *ignore,
>  {
>  	ktime_t tstamp = ktime_get_real();
>  	struct per_cpu_dm_data *data;
> +	struct net_dm_skb_cb *cb;
>  	struct sk_buff *nskb;
>  	unsigned long flags;
>  
> @@ -508,7 +520,9 @@ static void net_dm_packet_trace_kfree_skb_hit(void *ignore,
>  	if (!nskb)
>  		return;
>  
> -	NET_DM_SKB_CB(nskb)->pc = location;
> +	cb = NET_DM_SKB_CB(nskb);
> +	cb->reason = reason;
> +	cb->pc = location;
>  	/* Override the timestamp because we care about the time when the
>  	 * packet was dropped.
>  	 */
> @@ -606,8 +620,9 @@ static int net_dm_packet_report_in_port_put(struct sk_buff *msg, int ifindex,
>  static int net_dm_packet_report_fill(struct sk_buff *msg, struct sk_buff *skb,
>  				     size_t payload_len)
>  {
> -	u64 pc = (u64)(uintptr_t) NET_DM_SKB_CB(skb)->pc;
> +	struct net_dm_skb_cb *cb = NET_DM_SKB_CB(skb);
>  	char buf[NET_DM_MAX_SYMBOL_LEN];
> +	unsigned int reason;
>  	struct nlattr *attr;
>  	void *hdr;
>  	int rc;
> @@ -620,10 +635,16 @@ static int net_dm_packet_report_fill(struct sk_buff *msg, struct sk_buff *skb,
>  	if (nla_put_u16(msg, NET_DM_ATTR_ORIGIN, NET_DM_ORIGIN_SW))
>  		goto nla_put_failure;
>  
> -	if (nla_put_u64_64bit(msg, NET_DM_ATTR_PC, pc, NET_DM_ATTR_PAD))
> +	if (nla_put_u64_64bit(msg, NET_DM_ATTR_PC, (u64)(uintptr_t)cb->pc,
> +			      NET_DM_ATTR_PAD))
> +		goto nla_put_failure;
> +
> +	reason = (unsigned int)cb->reason;
> +	if (reason < SKB_DROP_REASON_MAX &&
> +	    nla_put_string(msg, NET_DM_ATTR_REASON, drop_reasons[reason]))

You need to make sure 'msg' has enough room for this attribute. Account
for it in net_dm_packet_report_size()

>  		goto nla_put_failure;
>  
> -	snprintf(buf, sizeof(buf), "%pS", NET_DM_SKB_CB(skb)->pc);
> +	snprintf(buf, sizeof(buf), "%pS", cb->pc);
>  	if (nla_put_string(msg, NET_DM_ATTR_SYMBOL, buf))
>  		goto nla_put_failure;
>  
> -- 
> 2.27.0
>