Re: st_* variables of ctim vs ctime vs ctimespec; is there a history & recommended use?

"Edward Sanford Sutton, III":

>   After recently finding stat(1) EXAMPLES error (I filed under PR274189 with
> patch and reasoning), I was trying to learn the meanings of these variables
> which lead me through reading stat(2) (found by `man lstat`) which says it
> uses st_mtim and provides both st_mtime and st_mtimespec for compatibility.
>   I didn't find any listed reason for the compatibility otherwise and
> wondered if that is documented somewhere.

Historically, in old Unix and POSIX, struct stat had fields st_mtime
etc. that were of type time_t and held a timestamp accurate to one
second.

At some point, computers got sufficiently fast that several things
could happen inside a single second, and higher precision timestamps
became desirable.  st_mtimespec etc. was added as a non-standard
BSD extension.  (Also, filesystems were changed to record such
timestamps in the first place.)

Eventually, POSIX recognized the need for higher precision timestamps
and standardized st_mtim etc.

"Compatibility" is about source-code compatibility with older code
bases.

-- 
Christian "naddy" Weisgerber                          naddy@mips.inka.de