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Go implementation of Linux Network Block Devices
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README.md

Go implementation of the Linux Network Block Device protocol

This repository contains Go implementations of

It's currently in beta and thus there are a bunch of known (and unknown) issues. Check the "beta" label for known problems. It is particularly interesting if you require features that are not yet supported. Please comment/vote on the corresponding issue.

Installation

Currently, this is pre-release, so the only way to install is from source. To do that, use

go get -u github.com/Merovius/nbd

Using the library

There are two packages:

  • nbd, containing the client and server implementations of the network protocol, as well as some convenience functions for nbdnl. The network protocol is used as a handshake between client and server, to negotiate optional features and other options. Under Linux, there are also a couple of functions provided to easily hook up a Device implementation and use it as a block device.
  • nbdnl, containing an implementation of the NBD generic netlink family, based on Matt Layher's genetlink package. This package can only be used on Linux; you should guard any usage with corresponding build tags.

The main usecase of this library is fuzzing code that tries to provide durable filesystem-operations. It allows you to implement aribtrary failure modes of a block device and then create any filesystem you'd like to test on it. For example, to fuzz for crash-resistence, you can have the block device return errors on any write-operations after an arbitrary point in time and then repeatedly mount a filesystem, run a bunch of application code, simulate a crash and then check invariants (after re-mounting). This can provide some confidence (though no guarantees) that your code works with actual filesystem-implementations.

Note, that any code that wants to configure the in-kernel NBD client has to be privileged (the process needs to have CAP_SYS_ADMIN).

NBD tool

This repo contains basic CLI tool to configure/serve/connect to NBD devices. You can install it via

go get -u github.com/Merovius/nbd/cmd/nbd

To see what it can do, use nbd help. Note, that most of the useful commands require root (or, more specifically, CAP_SYS_ADMIN) to work.

One of the most useful subcommands is lo, which can be used to use a file as a block device (similarly to losetup). It also supports toggling write-only mode of the device via a unix signal, though, which can be used to test the durability of software not written in Go. Refer to nbd help lo for details.

License

Copyright 2018 Axel Wagner

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
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