[Libguestfs] RFC for NBD protocol extension: extended headers

In response to this mail, I will be cross-posting a series of patches to multiple projects as a proof-of-concept implementation and request for comments on a new NBD protocol extension, called NBD_OPT_EXTENDED_HEADERS. With this in place, it will be possible for clients to request 64-bit zero, trim, cache, and block status operations when supported by the server. Not yet complete: an implementation of this in nbdkit. I also plan to tweak libnbd's 'nbdinfo --map' and 'nbdcopy' to take advantage of the larger block status results. Also, with 64-bit commands, we may want to also make it easier to let servers advertise an actual maximum size they are willing to accept for the commands in question (for example, a server may be happy with a full 64-bit block status, but still want to limit non-fast zero and cache to a smaller limit to avoid denial of service). -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org