Re: [Xen-devel] [PATCH for-4.5 1/2] xen/vsprintf: Introduce %*ph extended format specifier for hex buffers

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 26.09.14 at 12:10, <andrew.cooper3@xxxxxxxxxx> wrote:
> --- a/docs/misc/printk-formats.txt
> +++ b/docs/misc/printk-formats.txt
> @@ -18,3 +18,9 @@ Symbol/Function pointers:
>  
>         %pv     Domain and vCPU ID from a 'struct vcpu *' (printed as
>                 "d<domid>v<vcpuid>")
> +
> +
> +Raw buffer as hex string:
> +
> +       %*ph    Up to 64 characters, printed as "00 01 02 ... ff".  Buffer 
> length
> +               expected via the field_width paramter. i.e. printk("%*ph", 8, 
> buffer);

Let's keep this list sorted alphabetically please.

Also Linux supports an optional suffix (any of C, D, or N).

> --- a/xen/common/vsprintf.c
> +++ b/xen/common/vsprintf.c
> @@ -272,6 +272,31 @@ static char *pointer(char *str, char *end, const char 
> **fmt_ptr,
>      /* Custom %p suffixes. See XEN_ROOT/docs/misc/printk-formats.txt */
>      switch ( fmt[1] )
>      {
> +    case 'h': /* Raw buffer as hex string. */
> +    {
> +        /*
> +         * User expected to provide an explicit count using %*.  Bound 
> between
> +         * 0 and 64 bytes, defaulting to 0.
> +         */
> +        unsigned i, nr_bytes =
> +            ((field_width < 1) || (field_width > 64)) ? 0 : field_width;

Producing no output for too small a field width makes sense, but why
not print 64 bytes if more were requested?

> +        const uint8_t *hex_buffer = arg;
> +
> +        /* Consumed 'h' from the format string. */
> +        ++*fmt_ptr;
> +
> +        for ( i = 0; i < nr_bytes; ++i )
> +        {
> +            /* Each byte: 2 chars, 0-padded, base 16, no hex prefix. */
> +            str = number(str, end, hex_buffer[i], 16, 2, -1, ZEROPAD);
> +            if ( str < end )
> +                *str = ' ';
> +            ++str;

Could you suppress the trailing blank this produces, just like Linux
does?

Jan


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