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

[Dan Williams <dan.j.williams@intel.com>]

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 '%par', '%r', and '%pn'.
> %pra follows that struct range is similar to struct resource (%p[rR])
> but needs to be different.  Based on discussions with Petr and Andy
> '%pra' was chosen.[2]
> 
> Andy also suggested to keep the range prints similar to struct resource
> though combined code.  Add hex_range() to handle printing for both
> pointer types.
> 
> Finally introduce DEFINE_RANGE() as a parallel to DEFINE_RES_*() and use
> it in the tests.
> 
> Cc: Jonathan Corbet <corbet@lwn.net> (maintainer:DOCUMENTATION)
> Cc: linux-doc@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org (open list)
> Link: https://lore.kernel.org/all/663922b475e50_d54d72945b@dwillia2-xfh.jf.intel.com.notmuch/ [1]
> Link: https://lore.kernel.org/all/66cea3bf3332f_f937b29424@iweiny-mobl.notmuch/ [2]
> Suggested-by: "Dan Williams" <dan.j.williams@intel.com>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> 
> ---
> Changes:
> [iweiny: split from CXL patch set]
> [Andy: Define DEFINE_RANGE()]
> [Andy: rework hex_range() logic]
> [Andy: Don't use fallthrough]
> [Andy: clean up help comment]
> [Fan: clean up printk comment]
> [Rasmus: fix buf processing in hex_range()]
> [Rasmus: simplify buffer sizing]
> [Rasmus: add '[' to string]
> [Bagas: Clarify the start == end print behavior]
> ---
>  Documentation/core-api/printk-formats.rst | 13 +++++++
>  include/linux/range.h                     |  6 ++++
>  lib/test_printf.c                         | 17 +++++++++
>  lib/vsprintf.c                            | 57 +++++++++++++++++++++++++++----
>  4 files changed, 87 insertions(+), 6 deletions(-)
> 
> 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.