migration with exec giving truncated images

[Jim Paris <jim-XrPbb/hENzg@public.gmane.org>]

http://kvm.qumranet.com/kvmwiki/Migration suggests to use
 
  stop
  migrate "exec:dd of=STATEFILE"

to save an image that can be loaded later.  I was having trouble
getting this to work (loading gave "Migration failed rc=233") and
discovered that not all of the data was being saved, probably because
of some buffering/pipe issues.  I ran the following commands:

  (qemu) stop
  (qemu) migrate "exec:dd of=/tmp/jr1"
  (qemu) migrate "exec:cat > /tmp/jr2" 
  (qemu) migrate "exec:dd bs=1 of=/tmp/jr3"

And the file sizes:

  $ ls -al /tmp/jr[123]
  -rw-r--r--  1 root root    86061424 2007-08-02 16:52 jr1
  -rw-r--r--  1 root root    86220963 2007-08-02 16:53 jr2
  -rw-r--r--  1 root root    86220963 2007-08-02 16:56 jr3

Sometimes the "cat" gives a filesize similar to "dd", depending on
image size.  Only "dd bs=1" appears to always give me all of the data.
Sometimes the truncated images work fine for resume, other times they
cause a "migration failed".

I haven't had a chance yet to dig too deep in the source to find the
cause.  I haven't seeen if this truncation also happens over TCP.

This was tested with kvm-28 modules and both kvm-28 and kvm-33
userspace.  Has anyone else seen this?

-jim

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