block: add drive_backup HMP command

Make "drive_backup" available on the HMP monitor:

  drive_backup [-n] [-f] device target [format]

The -n flag requests QEMU to reuse the image found in new-image-file,
instead of recreating it from scratch.

The -f flag requests QEMU to copy the whole disk, so that the result
does not need a backing file.  Note that this flag *must* currently be
passed since the other sync modes ('none' and 'top') have not been
implemented yet.  Requiring it ensures that "drive_backup" behaves like
"drive_mirror".

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/hmp.h b/hmp.h
index 56d2e92..6c3bdcd 100644
--- a/hmp.h
+++ b/hmp.h
@@ -55,6 +55,7 @@
 void hmp_block_resize(Monitor *mon, const QDict *qdict);
 void hmp_snapshot_blkdev(Monitor *mon, const QDict *qdict);
 void hmp_drive_mirror(Monitor *mon, const QDict *qdict);
+void hmp_drive_backup(Monitor *mon, const QDict *qdict);
 void hmp_migrate_cancel(Monitor *mon, const QDict *qdict);
 void hmp_migrate_set_downtime(Monitor *mon, const QDict *qdict);
 void hmp_migrate_set_speed(Monitor *mon, const QDict *qdict);