Re: [PATCH RFCv3 2/3] lib/vsprintf.c: make %pD print full path for file

[Rasmus Villemoes <linux@rasmusvillemoes.dk>]

On 15/06/2021 08.48, Justin He wrote:
> Hi Petr
> 

>>> +   /* no filling space at all */
>>> +   if (buf >= end || !buf)
>>> +           return buf + reserved_size;
>>> +
>>> +   /* small space for long name */
>>> +   if (buf < end && prepend_len < 0)
>>> +           return string_truncate(buf, end, p, dpath_len, spec);
>>
>> We need this only because we allowed to write the path behind
>> spec.field_width. Do I get it right?
> 
> Both of field_width and precision:
> "%.14pD" or "%8.14pD"

Precision is never gonna be used with %p (or any of its kernel
extensions) because gcc would tell you

foo.c:5:13: warning: precision used with ‘%p’ gnu_printf format [-Wformat=]
    5 |  printf("%.5p\n", foo);

and there's no way -Wformat is going to be turned off to allow that usage.

IOW, there's no need to add complexity to make "%.3pD" of something that
would normally print "/foo/bar" merely print "/fo", similar to what a
precision with %s would mean.

As for field width, I don't know if it's worth honouring, but IIRC the
original %pd and %pD did that (that's where we have widen_string etc. from).

Other %p extensions put the field with to some other use (e.g. the
bitmap and hex string printing), so they obviously cannot simultaneously
use it in the traditional sense.

Rasmus