linux-kernel - Re: [PATCH v7 3/5] lib/vsprintf.c: make '%pD' print the full path of file

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Date:   Wed, 21 Jul 2021 15:55:44 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Jia He <justin.he@....com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Jonathan Corbet <corbet@....net>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Eric Biggers <ebiggers@...gle.com>,
        "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Matthew Wilcox <willy@...radead.org>,
        Christoph Hellwig <hch@...radead.org>, nd@....com
Subject: Re: [PATCH v7 3/5] lib/vsprintf.c: make '%pD' print the full path of
 file

On Thu 2021-07-15 09:14:05, Jia He wrote:
> Previously, the specifier '%pD' was for printing dentry name of struct
> file. It may not be perfect since by default it only prints one component.
> 
> As suggested by Linus [1]:
>   A dentry has a parent, but at the same time, a dentry really does
>   inherently have "one name" (and given just the dentry pointers, you
>   can't show mount-related parenthood, so in many ways the "show just
>   one name" makes sense for "%pd" in ways it doesn't necessarily for
>   "%pD"). But while a dentry arguably has that "one primary component",
>   a _file_ is certainly not exclusively about that last component.
> 
> Hence change the behavior of '%pD' to print the full path of that file.
> It is worthy of noting that %pD uses the entire given buffer as a scratch
> space. It might write something behind the trailing '\0' but never write
> beyond the scratch space.
> 
> Precision specifier is never going to be used with %p (or any of its
> kernel extensions) if -Wformat is turned on.
> 
> Link: https://lore.kernel.org/lkml/CAHk-=wimsMqGdzik187YWLb-ru+iktb4MYbMQG1rnZ81dXYFVg@mail.gmail.com/ [1]
> Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Jia He <justin.he@....com>

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr