linux-kernel - Re: [PATCH 2/3] printf: Add print format (%pra) for struct range

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Message-ID: <ZxZll3-NZreHlRaI@pathway.suse.cz>
Date: Mon, 21 Oct 2024 16:30:47 +0200
From: Petr Mladek <pmladek@...e.com>
To: Ira Weiny <ira.weiny@...el.com>
Cc: Dan Williams <dan.j.williams@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Jonathan Corbet <corbet@....net>,
	Davidlohr Bueso <dave@...olabs.net>,
	Jonathan Cameron <jonathan.cameron@...wei.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Alison Schofield <alison.schofield@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>,
	Fan Ni <fan.ni@...sung.com>, Bagas Sanjaya <bagasdotme@...il.com>,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-cxl@...r.kernel.org
Subject: Re: [PATCH 2/3] printf: Add print format (%pra) for struct range

On Sun 2024-10-20 21:49:50, Ira Weiny wrote:
> Dan Williams wrote:
> > Ira Weiny wrote:
> 
> [snip]
> 
> > > diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
> > > index 14e093da3ccd..e1ebf0376154 100644
> > > --- a/Documentation/core-api/printk-formats.rst
> > > +++ b/Documentation/core-api/printk-formats.rst
> > > @@ -231,6 +231,19 @@ width of the CPU data path.
> > >  
> > >  Passed by reference.
> > >  
> > > +Struct Range
> > > +------------
> > > +
> > > +::
> > > +
> > > +	%pra    [range 0x0000000060000000-0x000000006fffffff]
> > > +	%pra    [range 0x0000000060000000]
> > > +
> > > +For printing struct range.  struct range holds an arbitrary range of u64
> > > +values.  If start is equal to end only print the start value.
> > 
> > I was going to say "why this special case that does not exist for the
> > %pr case?", but then checked the code and found it *does* do this for %pr.
> > So if you're going to document this special case for %pra might as well
> > update the documentation for %pr too.
> > 
> > Alternatively, drop the new %pra documentation for this corner case as
> > accommodating the U64_MAX size range case is arguably a mistake in the
> > caller.
> > 
> > Either way, just make it consistent.
> 
> I've dropped the special case in the documentation.

I would actually prefer the opposite and update the %pr documentation.

The behavior might be surprising and people should beware of it,
for example when writing a parser for the output.

Best Regards,
Petr