Arnd Bergmann <arnd@xxxxxxxx> writes:
> On Friday, June 17, 2016 5:54:16 PM CEST Jeff Moyer wrote:
>> Jens Axboe <axboe@xxxxxxxxx> writes:
>>
>> > On 06/17/2016 05:36 PM, Steven Rostedt wrote:
>> >>
>> >> Jens,
>> >>
>> >> You want to take this, or do you want me to?
>> >
>> > I'll add it to my 4.8 tree, thanks Arnd.
>>
>> + /* need to check user space to see if this breaks in y2038 or y2106 */
>>
>> Userspace just uses it to print the timestamp, right? So do we need the
>> comment?
> If we have more details, the comment should describe what happens and
> when it overflows. If you have the source at hand, maybe you can answer
> these:
As far as I can tell, that value is only ever consulted when an
undocumented format option is given to blkparse. I don't think this
matters very much.
> How does it print the timestamp? Does it print the raw seconds value
> using %u (correct) or %d (incorrect), or does it convert it into
> year/month/day/hour/min/sec?
It converts it, but only prints hour/min/sec (and nsec):
struct timespec abs_start_time;
...
static void handle_notify(struct blk_io_trace *bit)
{
...
__u32 two32[2];
...
abs_start_time.tv_sec = two32[0];
abs_start_time.tv_nsec = two32[1];
if (abs_start_time.tv_nsec < 0) {
abs_start_time.tv_sec--;
abs_start_time.tv_nsec += 1000000000;
}
...
static const char *
print_time(unsigned long long timestamp)
{
static char timebuf[128];
struct tm *tm;
time_t sec;
unsigned long nsec;
sec = abs_start_time.tv_sec + SECONDS(timestamp);
nsec = abs_start_time.tv_nsec + NANO_SECONDS(timestamp);
if (nsec >= 1000000000) {
nsec -= 1000000000;
sec += 1;
}
tm = localtime(&sec);
snprintf(timebuf, sizeof(timebuf),
"%02u:%02u:%02u.%06lu",
tm->tm_hour,
tm->tm_min,
tm->tm_sec,
nsec / 1000);
return timebuf;
}
> In the last case, how does it treat second values above 0x80000000? Are
> those printed as year 2038 or year 1902?
We don't print the year.
> Are we sure that there is only one user space implementation that reads
> these values?
We're never sure about that. However, I'd be very surprised if anything
outside of blktrace used this.
Cheers,
Jeff
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