Re: [kvm-unit-tests RFC 1/3] lib: s390x: sclp: Add carriage return to line feed

[Janosch Frank <frankja@linux.ibm.com>]

On 6/30/23 17:12, Claudio Imbrenda wrote:
> On Fri, 30 Jun 2023 14:54:47 +0000
> Janosch Frank <frankja@linux.ibm.com> wrote:
> 
>> Without the \r the output of the ASCII console takes a lot of
>> additional effort to read in comparison to the line mode console.
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> ---
>>   lib/s390x/sclp-console.c | 15 ++++++++++++++-
>>   1 file changed, 14 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/s390x/sclp-console.c b/lib/s390x/sclp-console.c
>> index 19c74e46..384080b0 100644
>> --- a/lib/s390x/sclp-console.c
>> +++ b/lib/s390x/sclp-console.c
>> @@ -97,14 +97,27 @@ static void sclp_print_ascii(const char *str)
>>   {
>>   	int len = strlen(str);
>>   	WriteEventData *sccb = (void *)_sccb;
>> +	char *str_dest = (char *)&sccb->msg;
>> +	int i = 0;
>>   
>>   	sclp_mark_busy();
>>   	memset(sccb, 0, sizeof(*sccb));
>> +
>> +	for (; i < len; i++) {
>> +		*str_dest = str[i];
>> +		str_dest++;
>> +		/* Add a \r to the \n */
>> +		if (str[i] == '\n') {
>> +			*str_dest = '\r';
>> +			str_dest++;
>> +		}
>> +	}
>> +
>> +	len = (uintptr_t)str_dest - (uintptr_t)&sccb->msg;
> 
> some strings will therefore potentially overflow the SCCB
> 
> sclp_print() refuses to print more than 2kB, with this patch that limit
> could potentially be crossed
> 
> can you please briefly explain in a comment why that is ok? (or maybe
> that is not ok? then fix it somehow :) )

I'd like to see someone find a useful application for printing 2kb in a 
single printf() call.

Anyway, I could truncate the ASCII after the 2KB limit when adding the \r.

I'm wondering how the line-mode console interprets the \r. If it ignores 
it, then we could also convert to \n\r for both consoles and check for 
2kb when converting.