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 <[email protected]>
Reviewed-by: Eric Blake <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>
diff --git a/hmp-commands.hx b/hmp-commands.hx
index d1cdcfb..8c6b91a 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -1059,6 +1059,26 @@
 ETEXI
 
     {
+        .name       = "drive_backup",
+        .args_type  = "reuse:-n,full:-f,device:B,target:s,format:s?",
+        .params     = "[-n] [-f] device target [format]",
+        .help       = "initiates a point-in-time\n\t\t\t"
+                      "copy for a device. The device's contents are\n\t\t\t"
+                      "copied to the new image file, excluding data that\n\t\t\t"
+                      "is written after the command is started.\n\t\t\t"
+                      "The -n flag requests QEMU to reuse the image found\n\t\t\t"
+                      "in new-image-file, instead of recreating it from scratch.\n\t\t\t"
+                      "The -f flag requests QEMU to copy the whole disk,\n\t\t\t"
+                      "so that the result does not need a backing file.\n\t\t\t",
+        .mhandler.cmd = hmp_drive_backup,
+    },
+STEXI
+@item drive_backup
+@findex drive_backup
+Start a point-in-time copy of a block device to a specificed target.
+ETEXI
+
+    {
         .name       = "drive_add",
         .args_type  = "pci_addr:s,opts:s",
         .params     = "[[<domain>:]<bus>:]<slot>\n"