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SubjectRe: [PATCH v2] printf: add support for printing symbolic error codes
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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
>
> 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.
>
> With my embedded hat on, I've made it possible to remove this.
>
> 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.
>
> Acked-by: Uwe Kleine-König <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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