Re: [Xen-devel] [PATCH v2] xen/vsprintf: Introduce %pd formatter for domains

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 01/10/18 10:08, Jan Beulich wrote:
>>>> On 28.09.18 at 19:22, <andrew.cooper3@xxxxxxxxxx> wrote:
>> --- a/xen/common/vsprintf.c
>> +++ b/xen/common/vsprintf.c
>> @@ -264,6 +264,47 @@ static char *string(char *str, char *end, const char *s,
>>      return str;
>>  }
>>  
>> +/* Print a domain id, using names for system domains.  (e.g. d0 or d[IDLE]) 
>> */
>> +static char *print_domain(char *str, char *end, const struct domain *d)
>> +{
>> +    const char *name = NULL;
>> +
>> +    /* Some debugging may have an optionally-NULL pointer. */
>> +    if ( unlikely(!d) )
>> +        return string(str, end, "NULL", -1, -1, 0);
>> +
>> +    if ( str < end )
>> +        *str = 'd';
>> +
>> +    switch ( d->domain_id )
>> +    {
>> +    case DOMID_IO:   name = "[IO]";   break;
>> +    case DOMID_XEN:  name = "[XEN]";  break;
>> +    case DOMID_COW:  name = "[COW]";  break;
>> +    case DOMID_IDLE: name = "[IDLE]"; break;
>     default: ASSERT_UNREACHABLE();
>
> ?

No - specifically not in this case.

This path is used when printing crash information, and falling back to a
number is better behaviour than falling into an infinite loop,
overflowing the primary stack, then taking a #DF (which escalates to
triple fault on AMD), without printing anything useful.

In general, we cannot have BUG/WARN/ASSERTs in the middle vsprintf() path.

>
>> +    }
> Perhaps the insertion of 'd' might better live here, to make a
> better connection between the lack of a ++ there and the + 1
> below?

Will move.

>
>> +    if ( name )
>> +        return string(str + 1, end, name, -1, -1, 0);
>> +    else
>> +        return number(str + 1, end, d->domain_id, 10, -1, -1, 0);
>> +}
> Anyway, even without the adjustments
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Thanks,

~Andrew

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