linux-kernel - Re: [PATCH] printf: add support for printing symbolic error codes

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Message-ID: <7f744f43-3928-65a8-290b-ad1a45320210@kleine-koenig.org>
Date:   Mon, 2 Sep 2019 17:29:52 +0200
From:   Uwe Kleine-König <uwe@...ine-koenig.org>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Petr Mladek <pmladek@...e.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joe Perches <joe@...ches.com>, Juergen Gross <jgross@...e.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] printf: add support for printing symbolic error codes

Hello Rasmus,

On 8/30/19 11:46 PM, Rasmus Villemoes wrote:
> It has been suggested several times to extend vsnprintf() to be able
> to convert the numeric value of ENOSPC to print "ENOSPC". This is yet
> another attempt. Rather than adding another %p extension, simply teach
> plain %p to convert ERR_PTRs. While the primary use case is
> 
>   if (IS_ERR(foo)) {
>     pr_err("Sorry, can't do that: %p\n", foo);
>     return PTR_ERR(foo);
>   }
>
> it is also more helpful to get a symbolic error code (or, worst case,
> a decimal number) in case an ERR_PTR is accidentally passed to some
> %p<something>, rather than the (efault) that check_pointer() would
> result in.

Your text suggests that only cases that formerly emitted "(efault)" are
affected. I didn't check this but if this is the case, I like your patch.

> With my embedded hat on, I've made it possible to remove this.

I wonder if the config item should only be configurable if EXPERT is
enabled.

> I've tested that the #ifdeffery in errcode.c is sufficient to make
> this compile on arm, arm64, mips, powerpc, s390, x86 - I'm sure the
> 0day bot will tell me which ones I've missed.
> 
> The symbols to include have been found by massaging the output of
> 
>   find arch include -iname 'errno*.h' | xargs grep -E 'define\s*E'
> 
> In the cases where some common aliasing exists
> (e.g. EAGAIN=EWOULDBLOCK on all platforms, EDEADLOCK=EDEADLK on most),
> I've moved the more popular one (in terms of 'git grep -w Efoo | wc)
> to the bottom so that one takes precedence.
> 
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>

Apart from the above minor issues:

Acked-by: Uwe Kleine-König <uwe@...ine-koenig.org>

Best regards
Uwe



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