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

On Thu, 25 Jul 2024 13:32:52 +1000
David Gibson <david(a)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