Re: zero-length files in snapshots

[Chris Ball <cjb@laptop.org>]

Hi,

   > I often get zero-length files in btrfs snapshots (when the
   > original files were not zero-length).  The shell script below
   > reproduces this problem on two Ubuntu machines, with Ubuntu
   > kernels 2.6.31-17.54 and 2.6.32-12.17.  Is there some mistaken
   > assumption I'm making here in terms of how btrfsctl works?
   > [..]
   > 
   > echo x1 > /mnt/x/d/foo.txt || exit 2
   > btrfsctl -s /mnt/x/snap /mnt/x/d

You're just missing a sync/fsync() between these two lines.

We argued on IRC a while ago about whether this is a sensible default;
cmason wants the no-sync version of snapshot creation to be available,
but was amenable to the idea of changing the default to be sync before
snapshot, since it was pointed out that no-one other than him had
understood we were supposed to be running sync first.

- Chris.
-- 
Chris Ball   <cjb@laptop.org>
One Laptop Per Child