netdev - Re: [PATCH v6 net-next 1/7] netlink: Add a macro to set policy message with format string

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Message-ID: <pj41zla6032qn4.fsf@u570694869fb251.ant.amazon.com>
Date:   Thu, 23 Mar 2023 21:44:52 +0200
From:   Shay Agroskin <shayagr@...zon.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     Paolo Abeni <pabeni@...hat.com>,
        David Miller <davem@...emloft.net>, <netdev@...r.kernel.org>,
        "Woodhouse, David" <dwmw@...zon.com>,
        "Machulsky, Zorik" <zorik@...zon.com>,
        "Matushevsky, Alexander" <matua@...zon.com>,
        Saeed Bshara <saeedb@...zon.com>,
        "Wilson, Matt" <msw@...zon.com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        "Bshara, Nafea" <nafea@...zon.com>,
        "Belgazal, Netanel" <netanel@...zon.com>,
        "Saidi, Ali" <alisaidi@...zon.com>,
        "Herrenschmidt, Benjamin" <benh@...zon.com>,
        "Kiyanovski, Arthur" <akiyano@...zon.com>,
        "Dagan, Noam" <ndagan@...zon.com>,
        "Arinzon, David" <darinzon@...zon.com>,
        "Itzko, Shahar" <itzko@...zon.com>,
        "Abboud, Osama" <osamaabb@...zon.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Andrew Lunn <andrew@...n.ch>,
        Guangbin Huang <huangguangbin2@...wei.com>,
        Jie Wang <wangjie125@...wei.com>,
        Johannes Berg <johannes@...solutions.net>,
        Edward Cree <ecree.xilinx@...il.com>,
        "Florian Westphal" <fw@...len.de>
Subject: Re: [PATCH v6 net-next 1/7] netlink: Add a macro to set policy message with
 format string


Jakub Kicinski <kuba@...nel.org> writes:

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>
> On Thu, 23 Mar 2023 18:38:59 +0200 Shay Agroskin wrote:
>> Couldn't find a way to avoid both code duplication and 
>> evaluating
>> extact only once \= Submitted a new patchset with the modified
>> version of this macro.
>
> That's why we have the local variable called __extack, that we 
> *can*
> use multiple times, because it's a separate variable, (extack) 
> is
> evaluated only once, to initialize it...
>
> We don't need to copy the string formatting, unless I'm missing
> something. Paolo was just asking for:

There is an issue with shadowing __extack by NL_SET_ERR_MSG_FMT 
causing the changes to __extack not to be propagated back to the 
caller.
I'm not that big of an expert in C but changing __extack -> 
_extack fixes the shadowing issue.

Might not be the most robust solution, though it might suffice for 
this use case.

>
> -       NL_SET_ERR_MSG_FMT(extack, fmt, ##args);
> +       NL_SET_ERR_MSG_FMT(__extack, fmt, ##args);
>
> that's it.