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To:     Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jonathan Corbet <corbet@lwn.net>
Cc:     Andy Shevchenko <andy.shevchenko@gmail.com>,
        Joe Perches <joe@perches.com>, Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-doc@vger.kernel.org
References: <20190830214655.6625-1-linux@rasmusvillemoes.dk>
 <20190909203826.22263-1-linux@rasmusvillemoes.dk>
From:   =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= <uwe@kleine-koenig.org>
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Subject: Re: [PATCH v2] printf: add support for printing symbolic error codes
Message-ID: <33592303-091c-c480-460f-e2acd89e99be@kleine-koenig.org>
Date:   Mon, 16 Sep 2019 14:23:34 +0200
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From: =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= <uwe@kleine-koenig.org>
To: Rasmus Villemoes <linux@rasmusvillemoes.dk>,
 Andrew Morton <akpm@linux-foundation.org>, Jonathan Corbet <corbet@lwn.net>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>, Joe Perches
 <joe@perches.com>, Petr Mladek <pmladek@suse.com>,
 Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
 Jani Nikula <jani.nikula@linux.intel.com>,
 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
 linux-doc@vger.kernel.org
Message-ID: <33592303-091c-c480-460f-e2acd89e99be@kleine-koenig.org>
Subject: Re: [PATCH v2] printf: add support for printing symbolic error codes
References: <20190830214655.6625-1-linux@rasmusvillemoes.dk>
 <20190909203826.22263-1-linux@rasmusvillemoes.dk>
In-Reply-To: <20190909203826.22263-1-linux@rasmusvillemoes.dk>

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Hello Rasmus,

On 9/9/19 10:38 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
>=20
>   if (IS_ERR(foo)) {
>     pr_err("Sorry, can't do that: %p\n", foo);
>     return PTR_ERR(foo);
>   }
>=20
> 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.
>=20
> With my embedded hat on, I've made it possible to remove this.
>=20
> 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.
>=20
> The symbols to include have been found by massaging the output of
>=20
>   find arch include -iname 'errno*.h' | xargs grep -E 'define\s*E'
>=20
> In the cases where some common aliasing exists
> (e.g. EAGAIN=3DEWOULDBLOCK on all platforms, EDEADLOCK=3DEDEADLK on mos=
t),
> I've moved the more popular one (in terms of 'git grep -w Efoo | wc)
> to the bottom so that one takes precedence.
>=20
> Acked-by: Uwe Kleine-K=C3=B6nig <uwe@kleine-koenig.org>
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>

Even with my ack already given I still think having %pE (or %pe) for
ints holding an error code is sensible. So I wonder if it would be a
good idea to split this patch into one that introduces errcode() and
then the patch that teaches vsprintf about emitting its return value for
error valued pointers. Then I could rebase my initial patch for %pe on
top of your first one.

Other than that I wonder how we can go forward from here. So I think it
is time for v3 which picks up the few suggestions.

Best regards
Uwe


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