[PATCH] add keepalive for qemu-nbd

From: songlinfeng we want to export a image with qemu-nbd as server, in client we use libnbd to connect qemu-nbd,but when client power down,the server is still working. qemu-nbd will exit when last client exit.so,we still want server exit when client power down.maybe qmp can handle it,but i

[PATCH] try to find out which cluster allocated in qcow2

In our project,we want to full backup a disk only allocated area,but qmp block-dity-block-add can create a bitmap with all zero,so we can't find out which cluster is allocated.in qcow2,I think l2_table can help me find out which cluster should be backup. Signed-off-by: songlinfeng --- block