linux-kernel - Re: [PATCH v3 02/25] printk: Add print format (%par) for struct range

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Message-ID: <ZsyAZsDeWLNvSec9@pathway.suse.cz>
Date: Mon, 26 Aug 2024 15:17:26 +0200
From: Petr Mladek <pmladek@...e.com>
To: Ira Weiny <ira.weiny@...el.com>
Cc: Dave Jiang <dave.jiang@...el.com>, Fan Ni <fan.ni@...sung.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Navneet Singh <navneet.singh@...el.com>, Chris Mason <clm@...com>,
	Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>,
	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>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Alison Schofield <alison.schofield@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>,
	linux-btrfs@...r.kernel.org, linux-cxl@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	nvdimm@...ts.linux.dev
Subject: Re: [PATCH v3 02/25] printk: Add print format (%par) for struct range

On Thu 2024-08-22 12:53:32, Ira Weiny wrote:
> Petr Mladek wrote:
> > On Fri 2024-08-16 09:44:10, Ira Weiny wrote:
> > > The use of struct range in the CXL subsystem is growing.  In particular,
> > > the addition of Dynamic Capacity devices uses struct range in a number
> > > of places which are reported in debug and error messages.
> > > 
> > > To wit requiring the printing of the start/end fields in each print
> > > became cumbersome.  Dan Williams mentions in [1] that it might be time
> > > to have a print specifier for struct range similar to struct resource
> > > 
> > > A few alternatives were considered including '%pn' for 'print raNge' but
> > > %par follows that struct range is most often used to store a range of
> > > physical addresses.  So use '%par' for 'print address range'.
> > > 
> > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > > index 2d71b1115916..c132178fac07 100644
> > > --- a/lib/vsprintf.c
> > > +++ b/lib/vsprintf.c
> > > @@ -1140,6 +1140,39 @@ char *resource_string(char *buf, char *end, struct resource *res,
> > >  	return string_nocheck(buf, end, sym, spec);
> > >  }
> > >  
> > > +static noinline_for_stack
> > > +char *range_string(char *buf, char *end, const struct range *range,
> > > +		      struct printf_spec spec, const char *fmt)
> > > +{
> > > +#define RANGE_PRINTK_SIZE		16
> > > +#define RANGE_DECODED_BUF_SIZE		((2 * sizeof(struct range)) + 4)
> > > +#define RANGE_PRINT_BUF_SIZE		sizeof("[range - ]")

[...]

> > > +	static const struct printf_spec range_spec = {
> > > +		.base = 16,
> > > +		.field_width = RANGE_PRINTK_SIZE,
> 
> However, my testing indicates this needs to be.
> 
>                 .field_width = 18, /* 2 (0x) + 2 * 8 (bytes) */

Makes sense. Great catch!

> ... to properly zero pad the value.  Does that make sense?
>
> > > +		.precision = -1,
> > > +		.flags = SPECIAL | SMALL | ZEROPAD,
> > > +	};
> > > +
> > > +	*p++ = '[';
> > > +	p = string_nocheck(p, pend, "range ", str_spec);
> > > +	p = number(p, pend, range->start, range_spec);
> > > +	*p++ = '-';
> > > +	p = number(p, pend, range->end, range_spec);
> > > +	*p++ = ']';
> > > +	*p = '\0';

Best Regards,
Petr