[adding nbdkit readers] On 10/13/18 1:39 PM, Eric Wheeler wrote: Are you using qemu as the hypervisor? If you are using something else, like vmware, then using the kernel NBD module as the NBD client to expose the browser-as-server via /dev/nbd0 is reasonable since practically any hypervisor will attach to a raw block device. But if you are using qemu, I'd suggest that you use qemu directly as the NBD client, rather than indirecting through the kernel module (for that matter, qemu's NBD client knows how to efficiently handle sparse files if the server is capable, while to date the kernel nbd module does not). Since you are using virsh, the libvirt list is a better resource for figuring out the command line and/or XML changes to direct qemu to connect as an NBD client. The nbdkit project (under the libguestfs umbrella) has already implemented an NBD server that can bridge to an image served over http, if you want to use that as a starting point. Then the obvious question - do you really need to implement a solution using websockets through your browser in order to serve up a file on your desktop, or can you reuse existing solutions of a userspace NBD server to directly serve the file without involving the browser in the middle. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org