Re: [PATCH 04/11] log: Fix sub-second part in relative log time calculation

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 25 Jul 2024 13:32:52 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Wed, Jul 24, 2024 at 11:50:10PM +0200, Stefano Brivio wrote:
> >
> > [...]
> > 
> > +/**
> > + * logtime_fmt_and_arg() - Build format and arguments to print relative log time
> > + * @x:		Current timestamp
> > + */
> > +#define logtime_fmt_and_arg(x)						\
> > +	"%lli.%04lli",							\
> > +	((long long int)(x)->tv_sec - log_start.tv_sec),		\
> > +	(((long long int)(x)->tv_nsec - log_start.tv_nsec) / (100L * 1000))  
> 
> This doesn't look right.  If x->tv_nsec - log_start.tv_nsec is
> negative it will produce weird results.  Instead you need more complex
> logic to carry a sufficient difference in the nsec over into the
> seconds difference.

Oh, oops, of course.

I was hoping to recycle this from the Linux kernel, where we have
timespec_sub(), but that implementation looks a bit too complicated for
my taste. I'm adding something simpler now.

-- 
Stefano