linux-kernel - Re: [RFC 1/2] lib/vsprintf: Add support for pte

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Message-ID: <ihe6ueejcemrscqzuieunap6sk2z2yb7xr7szr77nue6qpcvm3@qnwvbvqlwdn5>
Date: Wed, 18 Jun 2025 19:16:00 +0100
From: Pedro Falcato <pfalcato@...e.de>
To: David Hildenbrand <david@...hat.com>
Cc: Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org, 
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Rasmus Villemoes <linux@...musvillemoes.dk>, 
	Sergey Senozhatsky <senozhatsky@...omium.org>, Petr Mladek <pmladek@...e.com>, 
	Steven Rostedt <rostedt@...dmis.org>, Jonathan Corbet <corbet@....net>, 
	Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [RFC 1/2] lib/vsprintf: Add support for pte_t

On Wed, Jun 18, 2025 at 10:44:20AM +0200, David Hildenbrand wrote:
> On 18.06.25 10:37, Anshuman Khandual wrote:
> > 
> > 
> > On 18/06/25 1:48 PM, David Hildenbrand wrote:
> > > On 18.06.25 06:12, Anshuman Khandual wrote:
> > > > Add a new format for printing page table entries.
> > > > 
> > > > Cc: Petr Mladek <pmladek@...e.com>
> > > > Cc: Steven Rostedt <rostedt@...dmis.org>
> > > > Cc: Jonathan Corbet <corbet@....net>
> > > > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > > > Cc: David Hildenbrand <david@...hat.com>
> > > > Cc: linux-doc@...r.kernel.org
> > > > Cc: linux-kernel@...r.kernel.org
> > > > Cc: linux-mm@...ck.org
> > > > Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> > > > ---
> > > >    Documentation/core-api/printk-formats.rst | 14 ++++++++++++++
> > > >    lib/vsprintf.c                            | 20 ++++++++++++++++++++
> > > >    mm/memory.c                               |  5 ++---
> > > >    scripts/checkpatch.pl                     |  2 +-
> > > >    4 files changed, 37 insertions(+), 4 deletions(-)
> > > > 
> > > > diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
> > > > index 4b7f3646ec6ce..75a110b059ee1 100644
> > > > --- a/Documentation/core-api/printk-formats.rst
> > > > +++ b/Documentation/core-api/printk-formats.rst
> > > > @@ -689,6 +689,20 @@ Rust
> > > >    Only intended to be used from Rust code to format ``core::fmt::Arguments``.
> > > >    Do *not* use it from C.
> > > >    +Page Table Entry
> > > > +----------------
> > > > +
> > > > +::
> > > > +        %ppte
> > > > +
> > > > +Print standard page table entry pte_t.
> > > > +
> > > > +Passed by reference.
> > > 
> > > Curious, why the decision to pass by reference?
> > 
> > Just to make this via %p<> based address mechanism. But wondering
> > will it be better for the pte to be represented via value instead
> > of reference ?
> 
> We commonly pass ptes to functions through value, not reference, that's why
> I am asking.


All printf/printk extensions in the kernel follow %p<some letters> and use
pointers because %p takes pointers, so it lets us use -Wformat with no issues.

So yes, taking a pte_t * is required.

-- 
Pedro