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

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Mon, 3 Jul 2023 13:46:29 +0200
Janosch Frank <frankja@linux.ibm.com> wrote:

> 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.

I'm with you there

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

sounds like a plan

> 
> 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.

is \n\r the right order? what about \r\n ?