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Date:   Thu, 13 Oct 2022 08:29:13 -0700
From:   Jakub Kicinski <kuba@kernel.org>
To:     <edward.cree@amd.com>
Cc:     <netdev@vger.kernel.org>, <linux-net-drivers@amd.com>,
        <davem@davemloft.net>, <pabeni@redhat.com>, <edumazet@google.com>,
        <habetsm.xilinx@gmail.com>, <johannes@sipsolutions.net>,
        <marcelo.leitner@gmail.com>, Edward Cree <ecree.xilinx@gmail.com>
Subject: Re: [RFC PATCH v2 net-next 1/3] netlink: add support for formatted
 extack messages
Message-ID: <20221013082913.0719721e@kernel.org>
In-Reply-To: <26c2cf2e699de83905e2c21491b71af0e34d00d8.1665567166.git.ecree.xilinx@gmail.com>
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        <26c2cf2e699de83905e2c21491b71af0e34d00d8.1665567166.git.ecree.xilinx@gmail.com>
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On Thu, 13 Oct 2022 10:23:00 +0100 edward.cree@amd.com wrote:
> +	if (snprintf(__extack->_msg_buf, NETLINK_MAX_FMTMSG_LEN,	\
> +		     (fmt), ##args) >= NETLINK_MAX_FMTMSG_LEN)		\
> +		net_warn_ratelimited("truncated extack: " fmt "\n",	\
> +				     ##args);				\
> +									\

Some "take it or leave it" comments:
 - Jiri's idea of always printing may be worth exploring
 - my preference would also be to produce a warning on overflow,
   rather than the exact print, because I always worry about people
   starting to depend on the print.

   And WARN_ON() is really heavy and may trigger remediations even
   tho truncated extack is just a minor nuisance.

   I'd do:

   pr(extack formatting overflow $__FILE__:$__func__:$__LINE__ $needed_len)
   
   (I think splicing the "trunced extack:" with fmt will result
    in the format string getting stored in .ro twice?)