netdev - Re: [PATCH v2 net-next 06/11] af_unix: Set drop reason in unix_stream

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Message-ID: <20250114170516.2a923a87@kernel.org>
Date: Tue, 14 Jan 2025 17:05:16 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Simon Horman
 <horms@...nel.org>, Donald Hunter <donald.hunter@...hat.com>, Kuniyuki
 Iwashima <kuni1840@...il.com>, <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 net-next 06/11] af_unix: Set drop reason in
 unix_stream_sendmsg().

On Sun, 12 Jan 2025 13:08:05 +0900 Kuniyuki Iwashima wrote:
> @@ -2249,14 +2265,13 @@ static int queue_oob(struct socket *sock, struct msghdr *msg, struct sock *other
>  static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
>  			       size_t len)
>  {
> +	enum skb_drop_reason reason;

I feel like we should draw the line somewhere for the reason codes.
We started with annotating packet drops in the stack, which are
otherwise hard to notice, we don't even have counters for all of them.
But at this point we're annotating sendmsg() errors? The fact we free
an skb on the error path seems rather coincidental for a sendmsg error.
IOW aren't we moving from packet loss annotation into general tracing
territory here?

If there is no ambiguity and application will get an error from a system
call I'd just use consume_skb().

I'm probably the most resistant to the drop reason codes, so I defer 
to Paolo / Eric for the real judgment...