Great new changes coming to nbdkit

Eric Blake has been doing some great stuff for nbdkit, the flexible plugin-based NBD server.

• Full parallel request handling.
  You’ve always been able to tell nbdkit that your plugin can handle multiple requests in parallel from a single client, but until now that didn’t actually do anything (only parallel requests from multiple clients worked).
• An NBD forwarding plugin, so if you have another NBD server which doesn’t support a feature like encryption or new-style protocol, then you can front that server with nbdkit which does.

As well as that he’s fixed lots of small bugs with NBD compliance so hopefully we’re now much closer to the protocol spec (we always check that we interoperate with qemu’s nbd client, but it’s nice to know that we’re also complying with the spec). He also fixed a potential DoS where nbdkit would try to handle very large writes which would delay a thread in the server indefinitely.

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Also this week, I wrote an nbdkit plugin for handling the weird Xen XVA file format. The whole thread is worth reading because 3 people came up with 3 unique solutions to this problem.