[libvirt] Allow nbd-backed disk images?

I am trying to use a qcow image with libvirt where the backing 'file' is a qemu-nbd server. Unfortunately the security code assumes that backingStore is always a real file so something like 'nbd:0:3333' is rejected because a file with that name cannot be accessed. A simple patch like the following works around the problem -- are there any suggestions on how to do this properly? Note that I am not worried about directly using nbd images. That would require a new disk type with XML markup, etc. I only want it to be permitted as a backingStore. diff --git a/src/util/storage_file.c b/src/util/storage_file.c index 6f48b10..7c0ea9a 100644 --- a/src/util/storage_file.c +++ b/src/util/storage_file.c @@ -292,6 +292,13 @@ qcowXGetBackingStore(char **res, return BACKING_STORE_INVALID; if (size + 1 == 0) return BACKING_STORE_INVALID; + + /* Short-circuit nbd backing files */ + if (size >= 4 && STRPREFIX((const char *)(buf + offset), "nbd:")) { + return BACKING_STORE_OK; + } + if (VIR_ALLOC_N(*res, size + 1) < 0) { virReportOOMError(); return BACKING_STORE_ERROR; -- Thanks, Adam