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From: Eric Blake <ebb9 AT byu DOT net>
Subject:  Re: MVFS results
Date: Fri, 17 Jul 2009 23:15:03 +0000 (UTC)
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Eric Blake <ebb9 <at> byu.net> writes:

> > As I said above, I assume that MVFS has a problem similar to what we
> > have for remote HPFS.  It's not sufficient to set only the minimal
> > set of access flags in calls to NtCreateFile/NtOpenFile in some
> > circumstances.  I can't tell where the problem is for cp -p since that
> > shouldn't call anything different from touch in terms of setting timestamps.
> 
> utimensat vs utimens?

Found the root cause.  R/O vs. writeable.  Doesn't matter where the source file 
lives; rather, the utimens call is failing because cp is changing the 
permissions to R/O prior to changing the times, all while keeping the same fd 
open that was used for populating the copy.  But touch starts from a closed fd, 
which is enough of a different path to trigger the workaround path that 
temporarily removes the R/O bit to change the time and then turn the bit back 
on.  Is that enough for you to go on, or do I need to also give strace details?

$ echo hi > /tmp/bar
$ touch -d yesterday /tmp/bar
$ cp -p /tmp/bar bar1
$ chmod a-w /tmp/bar
$ cp -p /tmp/bar bar2
$ ls -l bar?
-rw-r--r-- 1 eblake Domain Users 3 Jul 16 17:12 bar1
-r--r--r-- 1 eblake Domain Users 3 Jul 17 17:12 bar2

-- 
Eric Blake




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