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: <20230327103322.4f294683@kernel.org>
Date:   Mon, 27 Mar 2023 10:33:22 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Shay Agroskin <shayagr@...zon.com>
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

On Sat, 25 Mar 2023 16:49:34 +0300 Shay Agroskin wrote:
> > TBH the hierarchy should be the other way around, 
> > NL_SET_ERR_MSG_FMT()
> > should be converted to be:
> >
> > #define NL_SET_ERR_MSG_FMT(extack, attr, msg, args...) \
> >         NL_SET_ERR_MSG_ATTR_POL_FMT(extack, NULL, NULL, msg, 
> >         ##args)
> >
> > and that'd fix the shadowing, right?  
> 
> Well ... It will but it will contradict the current order of calls 
> as I see it.
> 
> NL_SET_ERR_MSG_FMT_MOD calls NL_SET_ERR_MSG_FMT which can be 
> described as 'the former extends the latter'.
> 
> On the other hand NL_SET_ERR_MSG_ATTR_POL implements the message 
> setting by itself and doesn't use NL_SET_ERR_MSG to set the 
> message.
> 
> So it seems like we already have two approaches for macro ordering 
> here and following your suggestion would create another type of 
> call direction of 'the former shrinks the latter by setting to 
> NULL its attributes'.
> Overall given the nature of C macros and the weird issues arise by 
> shadowing variables (ending up for some reason in not modifying 
> the pointer at all..) I'd say I mostly prefer V7 version which 
> re-implements the message setting and avoids creating such very 
> hard to find issues later.
> 
> Then again I'd follow your implementation suggestion if you still 
> prefer it (also I can modify the macro NL_SET_ERR_MSG to call 
> NL_SET_ERR_MSG_ATTR_POL to be consistent with the other change)

Alright, it doesn't matter all that much.