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Subjectboot time, process start time, and NOW time
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Even with the 2.6.7 kernel, I'm still getting reports of process
start times wandering. Here is an example:

"About 12 hours since reboot to 2.6.7 there was already a
difference of about 7 seconds between the real start time
and the start time reported by ps. Now, 24 hours since reboot
the difference is 10 seconds."

The calculation used is:

now - uptime + time_from_boot_to_process_start

The code shown below works great on a 2.4.xx or earlier kernel.
It generally relys on USER_HZ, which is supposedly in our ABI.

I have a feeling we'll forever be chasing bugs related to not
using a PLL to drive the clock tick at exactly HZ ticks per second.
Perhaps the DragonflyBSD code could be stolen. Anyway, the code:

///////////////////////////////////////////////////////////////////////////
unsigned long seconds_since_1970 = time(NULL);
unsigned long seconds_since_boot = uptime(0,0);
unsigned long time_of_boot = seconds_since_1970 - seconds_since_boot;
int pr_stime(char *restrict const outbuf, const proc_t *restrict const pp){
struct tm *proc_time;
struct tm *our_time;
time_t t;
const char *fmt;
int tm_year;
int tm_yday;
our_time = localtime(&seconds_since_1970); /* not reentrant */
tm_year = our_time->tm_year;
tm_yday = our_time->tm_yday;
t = time_of_boot + pp->start_time / Hertz;
proc_time = localtime(&t); /* not reentrant, this corrupts our_time */
fmt = "%H:%M"; /* 03:02 23:59 */
if(tm_yday != proc_time->tm_yday) fmt = "%b%d"; /* Jun06 Aug27 */
if(tm_year != proc_time->tm_year) fmt = "%Y"; /* 1991 2001 */
return strftime(outbuf, 42, fmt, proc_time);
}
///////////////////////////////////////////////////////////////////////////



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