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

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Message-ID: <ZsSjdjzRSG87alk5@pathway.suse.cz>
Date: Tue, 20 Aug 2024 16:08:54 +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 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'.
> 
> --- a/Documentation/core-api/printk-formats.rst
> +++ b/Documentation/core-api/printk-formats.rst
> @@ -231,6 +231,20 @@ width of the CPU data path.
>  
>  Passed by reference.
>  
> +Struct Range
> +------------
> +
> +::
> +
> +	%par	[range 0x60000000-0x6fffffff] or

It seems that it is always 64-bit. It prints:

struct range {
	u64   start;
	u64   end;
};

> +		[range 0x0000000060000000-0x000000006fffffff]
> +
> +For printing struct range.  A variation of printing a physical address is to
> +print the value of struct range which are often used to hold a physical address
> +range.
> +
> +Passed by reference.
> +
>  DMA address types dma_addr_t
>  ----------------------------
>  
> 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 - ]")

I think that it should be "[range -]"

> +	char sym[RANGE_DECODED_BUF_SIZE + RANGE_PRINT_BUF_SIZE];
> +	char *p = sym, *pend = sym + sizeof(sym);
> +
> +	static const struct printf_spec str_spec = {
> +		.field_width = -1,
> +		.precision = 10,
> +		.flags = LEFT,
> +	};

Is this really needed? What about using "default_str_spec" instead?

> +	static const struct printf_spec range_spec = {
> +		.base = 16,
> +		.field_width = RANGE_PRINTK_SIZE,
> +		.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';
> +
> +	return string_nocheck(buf, end, sym, spec);
> +}
> +
>  static noinline_for_stack
>  char *hex_string(char *buf, char *end, u8 *addr, struct printf_spec spec,
>  		 const char *fmt)

Also add a selftest into lib/test_printf.c, please.

Best Regards,
Petr