rsync - Dec 2014 - Modification time error

I was struggling tracking down a strange behaviour and could reproduce it
with the testsuite. After patching it with:

--- a/testsuite/compare-dest.test	2007-09-03 22:43:58.000000000 +0200
+++ b/testsuite/compare-dest.test	2014-12-30 19:28:32.060267390 +0100
@@ -18,6 +18,7 @@

 # Setup the alt and chk dirs
 $RSYNC -av --include=text --include='*/' --exclude='*'
"$fromdir/" "$alt1dir/"
+stat -c %y "$fromdir/text" "$alt1dir/text"
 $RSYNC -av --include=etc-ltr-list --include='*/' --exclude='*'
"$fromdir/" "$alt2dir/"

 sleep 1
@@ -34,4 +35,4 @@
     '$fromdir/' '$todir/'" "$fromdir"
"$todir"

 # The script would have aborted on error, so getting here means we've won.
-exit 0
+exit 99

in order to examine and preserve the data, I found:

2014-12-30 19:29:01.806934641 +0100
2014-12-30 19:29:01.820267972 +0100

in the test.log, e.g. the created file's mtime differs!

Surprisingly, the same command did work when calling it from the command line
after changing to the data directory:

# cd testtmp/compare-dest
# /tmp/rsync-3.1.1/rsync -av --include=text --include='*/'
--exclude='*' /tmp/rsync-3.1.1/testtmp/compare-dest/from/
/tmp/rsync-3.1.1/testtmp/compare-dest/alt3/
# stat -c %y /tmp/rsync-3.1.1/testtmp/compare-dest/from/text
/tmp/rsync-3.1.1/testtmp/compare-dest/alt3/text
2014-12-30 19:29:01.806934641 +0100
2014-12-30 19:29:01.806934641 +0100

Correct mtime (as it should be).

Is there any reasonable explanation for this?!

I was using Knoppix 7.4.1 (Kernel 3.16.2) on a mounted ext4 filesystem.

Ingo

/tmp was actually on a tmpfs and no idea why this happens, but it doesn't
seem to be a rsync issue (though it's kinda scary). This "fixes"
it:

diff -Nur a/testsuite/compare-dest.test b/testsuite/compare-dest.test
--- a/testsuite/compare-dest.test	2007-09-03 22:43:58.000000000 +0200
+++ b/testsuite/compare-dest.test	2014-12-31 10:40:43.796572443 +0100
@@ -15,6 +15,7 @@
 # Build some files/dirs/links to copy

 hands_setup
+sleep 1

 # Setup the alt and chk dirs
 $RSYNC -av --include=text --include='*/' --exclude='*'
"$fromdir/" "$alt1dir/"

On Wed, Dec 31, 2014 at 2:34 AM, Ingo Br?ckl <ib at wupperonline.de>
wrote:
> /tmp was actually on a tmpfs and no idea why this happens

Thanks for pointing that out.  I couldn't reproduce the issue until I ran
the tests on a tmpfs mount, and discovered that rsync is optimizing away a
utimensat() call if it thinks that the file already has the right time set
(which is just a comparison of the mtime integer seconds).  So, the faster
run on a tmpfs mount caused the initial rsync copy to not bother to set the
nanosecond time value on the newly created file.  I'll look into a fix for
this soon.

..wayne..
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