Re: [Xen-devel] [PATCH v2] cmdline: treat hyphens and underscores the same

["Durrant, Paul" <pdurrant@xxxxxxxxxxxx>]

> -----Original Message-----
> From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of Jan
> Beulich
> Sent: 23 January 2020 11:43
> To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>; Julien Grall
> <julien@xxxxxxx>; Wei Liu <wl@xxxxxxx>; Konrad Wilk
> <konrad.wilk@xxxxxxxxxx>; George Dunlap <George.Dunlap@xxxxxxxxxxxxx>;
> Andrew Cooper <andrew.cooper3@xxxxxxxxxx>; Ian Jackson
> <ian.jackson@xxxxxxxxxx>
> Subject: [Xen-devel] [PATCH v2] cmdline: treat hyphens and underscores the
> same
> 
> In order to avoid permanently having to ask that no new command line
> options using underscores be introduced (albeit I'm likely to still make
> remarks), and in order to also allow extending the use of hyphens to
> pre-existing ones, introduce custom comparison functions treating both
> characters as matching.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> v2: Rename to opt_str{,n}cmp(). Don't use the new function for comapring
>     against "no-" in parse_params(). Add comment to cdiff().
> 
> --- a/docs/misc/xen-command-line.pandoc
> +++ b/docs/misc/xen-command-line.pandoc
> @@ -72,6 +72,11 @@ Some options take a comma separated list
>  Some parameters act as combinations of the above, most commonly a mix
>  of Boolean and String.  These are noted in the relevant sections.
> 
> +### Spelling
> +
> +Parameter names may include hyphens or underscores.  These are
> +generally being treated as matching one another by the parsing logic.
> +
>  ## Parameter details
> 
>  ### acpi
> --- a/xen/common/kernel.c
> +++ b/xen/common/kernel.c
> @@ -23,6 +23,53 @@ enum system_state system_state = SYS_STA
>  xen_commandline_t saved_cmdline;
>  static const char __initconst opt_builtin_cmdline[] = CONFIG_CMDLINE;
> 
> +/*
> + * Calculate the difference between two characters for command line
> parsing
> + * purposes, i.e. treating '-' and '_' the same.
> + */
> +static int cdiff(unsigned char c1, unsigned char c2)
> +{
> +    int res = c1 - c2;
> +
> +    if ( res && (c1 ^ c2) == ('-' ^ '_') &&
> +         (c1 == '-' || c1 == '_') )
> +        res = 0;
> +

Wow! That makes my head hurt. How about:

static int cdiff(unsigned char c1, unsigned char c2)
{
    if ( c1 == '-' )
        c1 = '_';

    if ( c2 == '-' )
        c2 = '_';

    return c1 - c2;
}

?

  Paul
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