linux-kernel - Re: [PATCH v4 1/1] printf: add support for printing symbolic error names

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Message-ID: <20191014055114.GA5045@taurus.defre.kleine-koenig.org>
Date:   Mon, 14 Oct 2019 07:51:14 +0200
From:   Uwe Kleine-König <uwe@...ine-koenig.org>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Joe Perches <joe@...ches.com>, Petr Mladek <pmladek@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH v4 1/1] printf: add support for printing symbolic error
 names

On Fri, Oct 11, 2019 at 03:36:17PM +0200, 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
> implements that as a %p extension: With %pe, one can do
> 
>   if (IS_ERR(foo)) {
>     pr_err("Sorry, can't do that: %pe\n", foo);
>     return PTR_ERR(foo);
>   }
> 
> instead of what is seen in quite a few places in the kernel:
> 
>   if (IS_ERR(foo)) {
>     pr_err("Sorry, can't do that: %ld\n", PTR_ERR(foo));
>     return PTR_ERR(foo);
>   }
> 
> If the value passed to %pe is an ERR_PTR, but the library function
> errname() added here doesn't know about the value, the value is simply
> printed in decimal. If the value passed to %pe is not an ERR_PTR, we
> treat it as an ordinary %p and thus print the hashed value (passing
> non-ERR_PTR values to %pe indicates a bug in the caller, but we can't
> do much about that).
> 
> With my embedded hat on, and because it's not very invasive to do,
> I've made it possible to remove this. The errname() function and
> associated lookup tables take up about 3K. For most, that's probably
> quite acceptable and a price worth paying for more readable
> dmesg (once this starts getting used), while for those that disable
> printk() it's of very little use - I don't see a
> procfs/sysfs/seq_printf() file reasonably making use of this - and
> they clearly want to squeeze vmlinux as much as possible. Hence the
> default y if PRINTK.
> 
> 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>

I like having an explicit code even better than relying on a plain %p to
emit the code. So please readd my

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

Best regards
Uwe

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