Arnd Bergmann arnd@arndb.de writes:
On Friday, June 17, 2016 5:54:16 PM CEST Jeff Moyer wrote:
Jens Axboe axboe@kernel.dk 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