This patch adds the -drive copy-on-read=on|off command-line option:
copy-on-read=on|off
copy-on-read is "on" or "off" and enables whether to copy read backing
file sectors into the image file. Copy-on-read avoids accessing the
same backing file sectors repeatedly and is useful when the backing
file is over a slow network. By default copy-on-read is off.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>