block: add -drive copy-on-read=on|off

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 <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>
diff --git a/hmp-commands.hx b/hmp-commands.hx
index f8d855e..79a9195 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -860,9 +860,10 @@
         .args_type  = "pci_addr:s,opts:s",
         .params     = "[[<domain>:]<bus>:]<slot>\n"
                       "[file=file][,if=type][,bus=n]\n"
-                      "[,unit=m][,media=d][index=i]\n"
+                      "[,unit=m][,media=d][,index=i]\n"
                       "[,cyls=c,heads=h,secs=s[,trans=t]]\n"
-                      "[snapshot=on|off][,cache=on|off]",
+                      "[,snapshot=on|off][,cache=on|off]\n"
+                      "[,readonly=on|off][,copy-on-read=on|off]",
         .help       = "add drive to PCI storage controller",
         .mhandler.cmd = drive_hot_add,
     },