On NFS, cp -a copies non-integer timestamp as integer timestamp?

[David Wuertele]

I struggled for a while with the following situation:

1.  make on my local disk works fine: a subsequent make says "nothing to be 
done"
2.  make on my NFS mount builds everything correctly, but a subsequent make
complains that I have to rebuild stuff

I knew that there shouldn't be any rebuilding necessary, so I found the first
file that make claims was out of date, and checked its timestamps.  What I found
was that the dependency (file being copied by cp -a) had a non-integral mtime,
but the target always had an integer mtime:

$ make > make4.out 2>&1
$ make -n -d > make5.out 2>&1
$ grep -B1 'Must remake target' make5.out | grep 'is newer than target' | head 
-1
                 Prerequisite `/path/to/staging/busybox-1.4.0/bin/busybox' is
newer than target `/path/to/deploy/box_x86_debug/bin/busybox'.
$ stat /path/to/staging/busybox-1.4.0/bin/busybox
/path/to/deploy/box_x86_debug/bin/busybox 
  File: `/path/to/staging/busybox-1.4.0/bin/busybox'
  Size: 560140          Blocks: 1104       IO Block: 32768  regular file
Device: 26h/38d Inode: 2335853     Links: 1
Access: (0755/-rwxr-xr-x)  Uid: (10059/  qwv684)   Gid: (10001/ma29cu01)
Access: 2007-05-14 21:32:46.147767000 -0400
Modify: 2007-05-14 21:32:46.154757000 -0400
Change: 2007-05-14 21:32:48.284627000 -0400
  File: `/path/to/deploy/box_x86_debug/bin/busybox'
  Size: 560140          Blocks: 1104       IO Block: 32768  regular file
Device: 26h/38d Inode: 20095217    Links: 1
Access: (0755/-rwxr-xr-x)  Uid: (10059/  qwv684)   Gid: (10001/ma29cu01)
Access: 2007-05-14 21:32:46.000000000 -0400
Modify: 2007-05-14 21:32:46.000000000 -0400
Change: 2007-05-14 21:48:56.102837000 -0400
$


Here is the rule that copied one file to the other:

$ make nothing -p | grep -A7 /path/to/deploy/box_x86_debug/bin/busybox:
/path/to/deploy/box_x86_debug/bin/busybox:
/path/to/staging/busybox-1.4.0/bin/busybox
#  Implicit rule search has not been done.
#  Implicit/static pattern stem: `bin/busybox'
#  Modification time never checked.
#  File has not been updated.
#  commands to execute (from `make/busybox.mk', line 295):
        mkdir -p $(@D) && cp -af $< $@
        

I tried to reproduce this behavior, but could not:

$ touch test
$ cp -af test test2
$ stat test test2
  File: `test'
  Size: 0               Blocks: 0          IO Block: 32768  regular empty file
Device: 26h/38d Inode: 15119606    Links: 1
Access: (0644/-rw-r--r--)  Uid: (10059/  qwv684)   Gid: (10001/ma29cu01)
Access: 2007-05-14 22:48:01.058211000 -0400
Modify: 2007-05-14 22:48:01.058211000 -0400
Change: 2007-05-14 22:48:01.058211000 -0400
  File: `test2'
  Size: 0               Blocks: 0          IO Block: 32768  regular empty file
Device: 26h/38d Inode: 6176374     Links: 1
Access: (0644/-rw-r--r--)  Uid: (10059/  qwv684)   Gid: (10001/ma29cu01)
Access: 2007-05-14 22:48:01.058211000 -0400
Modify: 2007-05-14 22:48:01.058211000 -0400
Change: 2007-05-14 22:48:05.858411000 -0400

As you can see, in this case, cp -a copied the fractional portion of the mtime.

Can anyone explain why cp -a might copy the fractional portion of the mtime
*sometimes* but not others?

Dave