Re: [Xen-devel] [PATCH RFC] xen/vsprintf: Introduce %pd formatter for domains

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.08.18 at 15:06, <andrew.cooper3@xxxxxxxxxx> wrote:
> This allows all system domids to be printed by name, rather than special
> casing the idle vcpus alone.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Tim Deegan <tim@xxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Julien Grall <julien.grall@xxxxxxx>
> 
> RFC, because this was proposed before but rejected at the time.  I'm looking
> to try and turn errors like this:
> 
>   (XEN) mm.c:1023:d0v2 pg_owner d32754 l1e_owner d0, but real_pg_owner d0
>   (XEN) mm.c:1099:d0v2 Error getting mfn 810020 (pfn 59db1) from L1 entry 
> 8000000810020227 for l1e_owner d0, pg_owner d32754
> 
> into the slightly more helpful:
> 
>   (XEN) mm.c:1022:d0v2 pg_owner dXEN l1e_owner d0, but real_pg_owner d0
>   (XEN) mm.c:1098:d0v2 Error getting mfn 810020 (pfn 59db1) from L1 entry 
> 8000000810020227 for l1e_owner d0, pg_owner dXEN
> 
> although even in this case, the former printk has an awkward corner case of a
> possibly NULL domain pointer, which can possibly only reasonably be fixed
> inside pointer() itself.

Or in print_domain(), producing "NULL".

> --- a/docs/misc/printk-formats.txt
> +++ b/docs/misc/printk-formats.txt
> @@ -28,5 +28,8 @@ Symbol/Function pointers:
>  
>  Domain and vCPU information:
>  
> +       %pd     Domain from a 'struct domain *d' (printed as d<domid>, but 
> with
> +               system domains represented by name, e.g. 'dIDLE')

This looks a little awkward - how about d<IDLE> etc?

> --- a/xen/common/vsprintf.c
> +++ b/xen/common/vsprintf.c
> @@ -264,6 +264,41 @@ static char *string(char *str, char *end, const char *s,
>      return str;
>  }
>  
> +/* Print a domain as d<num> or d<str> for system domains. */
> +static char *print_domain(char *str, char *end, const struct domain *d)
> +{
> +    const char *name = NULL;
> +
> +    if ( str < end )
> +        *str++ = 'd';

I would guess you've copied this idiom from somewhere, and if so
it would be good to know where we still have got such broken
construct(s) left: The increment needs to happen outside of the
if(), for snprintf() et al to return a large enough number. See e.g.
string(). Perhaps best to do this like you do ...

> +static char *print_vcpu(char *str, char *end, const struct vcpu *v)
> +{
> +    str = print_domain(str, end, v->domain);
> +
> +    if ( str < end )
> +        *str = 'v';
> +
> +    return number(str + 1, end, v->vcpu_id, 10, -1, -1, 0);

... here.

Jan



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