How to retrieve file times with nanosecond precision?

Question

I've just discovered that the stat() call, and the corresponding struct stat, does not contain fields for the file times with precision greater than one second. For setting these times, there are a variety of {f,l}utime{n,}s() functions, but not for getting.

How then does obtain these times with nanosecond precision, preferably using POSIX API?

Answer 1

The stat structure returned by stat() itself has been upgraded for POSIX.1-2008.

The struct stat structure contains the three modification times as:

struct timespec st_atim - Last data access timestamp. 
struct timespec st_mtim - Last data modification timestamp. 
struct timespec st_ctim - Last file status change timestamp.

(from this OpenGroup link here under Headers, <sys/stat.h>) and that struct timespec is defined there (in <time.h>) as containing at least:

time_t  tv_sec          - Seconds. 
long    tv_nsec         - Nanoseconds. 

Previously, these three times were time_t values with their one-second resolution.

Answer 2

Most file systems dont hold such accurate timestamps. From here:

Most file systems, including ext3, include timestamp data that is accurate to a second. Ext4 extends the accuracy of this data to a nanosecond. Some sources also indicate that the ext4 timestamps support dates through April 25, 2514, versus January 18, 2038, for ext3