On Tue, 26 Aug 2025 at 12:42, Daniel P. Berrangé <[email protected]> wrote:
>
> On Fri, Aug 22, 2025 at 02:26:44PM +0200, Paolo Bonzini wrote:
> > This simplifies the Python code and reduces the size of the tracepoints.
> > +void ftrace_write(const char *fmt, ...)
> > +{
> > + char ftrace_buf[MAX_TRACE_STRLEN];
> > + int unused __attribute__ ((unused));
> > + int trlen;
> > + va_list ap;
> > +
> > + va_start(ap, fmt);
> > + trlen = vsnprintf(ftrace_buf, MAX_TRACE_STRLEN, fmt, ap);
> > + va_end(ap);
> > +
> > + trlen = MIN(trlen, MAX_TRACE_STRLEN - 1);
> > + unused = write(trace_marker_fd, ftrace_buf, trlen);
>
> You're just copying the existing code pattern which is fine for now so
>
> Reviewed-by: Daniel P. Berrangé <[email protected]>
>
>
> More generally though, IMHO, QEMU would be better off bringing in
> gnulib's 'ignore_value' macro, but simplified since we don't care
> about ancient GCC
>
> #define ignore_value(x) \
> (__extension__ ({ __typeof__ (x) __x = (x); (void) __x; }))
>
> so that we don't need to play games with extra variables. eg
>
> ignore_value(write(trace_marker_fd, ftrace_buf, trlen));
Isn't there a way to write that that explicitly tells
the compiler "this is unused" (i.e. with the 'unused'
attribute) rather than relying on a particular construct
to not trigger a warning?
-- PMM
