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From:   Justin He <Justin.He@arm.com>
To:     Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Petr Mladek <pmladek@suse.com>
CC:     Steven Rostedt <rostedt@goodmis.org>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Eric Biggers <ebiggers@google.com>,
        "Ahmed S. Darwish" <a.darwish@linutronix.de>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: RE: [PATCH RFCv3 2/3] lib/vsprintf.c: make %pD print full path for
 file
Thread-Topic: [PATCH RFCv3 2/3] lib/vsprintf.c: make %pD print full path for
 file
Thread-Index: AQHXXtruU5AIb64vzESDK9b2+VqurKsTqaKAgAD8LoCAAAitgIAAAHTA
Date:   Tue, 15 Jun 2021 07:18:01 +0000
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> -----Original Message-----
> From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Sent: Tuesday, June 15, 2021 3:15 PM
> To: Justin He <Justin.He@arm.com>; Petr Mladek <pmladek@suse.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>; Sergey Senozhatsky
> <senozhatsky@chromium.org>; Andy Shevchenko
> <andriy.shevchenko@linux.intel.com>; Rasmus Villemoes
> <linux@rasmusvillemoes.dk>; Jonathan Corbet <corbet@lwn.net>; Alexander
> Viro <viro@zeniv.linux.org.uk>; Linus Torvalds <torvalds@linux-
> foundation.org>; Peter Zijlstra (Intel) <peterz@infradead.org>; Eric
> Biggers <ebiggers@google.com>; Ahmed S. Darwish <a.darwish@linutronix.de>=
;
> linux-doc@vger.kernel.org; linux-kernel@vger.kernel.org; linux-
> fsdevel@vger.kernel.org
> Subject: Re: [PATCH RFCv3 2/3] lib/vsprintf.c: make %pD print full path f=
or
> file
>
> On 15/06/2021 08.48, Justin He wrote:
> > Hi Petr
> >
>
> >>> +   /* no filling space at all */
> >>> +   if (buf >=3D 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 =EF=BF=BD%p=EF=BF=BD gnu_printf =
format [-
> Wformat=3D]
>     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.
>
Aha, this answer my question in last email.
Thank you


--
Cheers,
Justin (Jia He)


> 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. fro=
m).
>
> 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
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