At least in Ken fs, you want the access time of the root (to get the current fs time):
; date; ls -ldu /n/boot /
Sat Feb 11 17:45:13 PST 2006
d-r-xr-xr-x / 0 bootes bootes 0 Feb 11 17:45 /
d-rwxrwxr-x M 251502 adm sys 0 Feb 11 17:45 /n/boot
It's done here, 9p1.c:1300,1301:
if(d->qid.path == QPROOT) /* stat of root gives time */
d->atime = time();
and here, 9p2.c:1431,1432:
if(d->qid.path == QPROOT) /* stat of root gives time */
d->atime = time();
I haven't looked to see if fossil does it.
