netdev - Re: [PATCH] json_print: fix print_uint with helper type extensions

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Message-ID: <20180316133437.5f535a0e@xeon-e3>
Date:   Fri, 16 Mar 2018 13:34:37 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Kevin Darbyshire-Bryant <ldir@...byshire-bryant.me.uk>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH] json_print: fix print_uint with helper type extensions

On Thu, 15 Mar 2018 20:07:20 +0000
Kevin Darbyshire-Bryant <ldir@...byshire-bryant.me.uk> wrote:

> Introduce print helper functions for int, uint, explicit int32, uint32,
> int64 & uint64.
> 
> print_int used 'int' type internally, whereas print_uint used 'uint64_t'
> 
> These helper functions eventually call vfprintf(fp, fmt, args) which is
> a variable argument list function and is dependent upon 'fmt' containing
> correct information about the length of the passed arguments.
> 
> Unfortunately print_int v print_uint offered no clue to the programmer
> that internally passed ints to print_uint were being promoted to 64bits,
> thus the format passed in 'fmt' string vs the actual passed integer
> could be different lengths.  This is even more interesting on big endian
> architectures where 'vfprintf' would be looking in the middle of an
> int64 type and hence produced wildly incorrect values in tc qdisc
> output.
> 
> print_u/int now stick with native int size.  print_u/int32 & print
> u/int64 functions offer explicit integer sizes.
> 
> To portably use these formats you should use the relevant PRIdN or PRIuN
> formats as defined in inttypes.h
> 
> e.g.
> 
> print_uint64(PRINT_ANY, "refcnt", "refcnt %" PRIu64 " ", t->tcm_info)
> 
> Signed-off-by: Kevin Darbyshire-Bryant <ldir@...byshire-bryant.me.uk>

I am fine with this. But since there is no code using it yet, it should
go net-next branch.

Reviewed-by: Stephen Hemminger <stephen@...workplumber.org>