Golang bindings for both libnbd and nbdkit

I have to say for full transparency up front that Golang is not my favourite programming language, even less after using it for a while. Nevertheless with a lot of help from Dan Berrangé we now have Golang bindings for libnbd and nbdkit which are respectively client and server software for the Linux Network Block Device protocol.

The Golang bindings for libnbd let you connect to a server and read and write from it. This is all pretty straightforward so read the manual page if you want to find out more.

The Golang bindings for nbdkit are considerably more interesting because you can use them to write pretty natural and high performance NBD servers to expose “interesting things”.

I’m hoping in particular there are interesting block device sources in the Kubernetes / Docker ecosystem which are probably only available from Golang that we could now expose to other software (although I’m also still researching this area so I don’t yet know what in particular).

You can make a complete Golang NBD server really easily now with only a few lines of code. Minus boilerplate, something like this is sufficient (see this link for complete working examples):

type MyPlugin struct {
	nbdkit.Plugin
}

type MyConnection struct {
	nbdkit.Connection
}

func (p *MyPlugin) Open(readonly bool) (nbdkit.ConnectionInterface, error) {
	return &MyConnection{}, nil
}

func (c *MyConnection) GetSize() (uint64, error) {
	return size, nil
}

func (c *MyConnection) PRead(buf []byte, offset uint64,
	flags uint32) error {
	copy(buf, ... from the source of your data here ...)
	return nil
}

func (c *MyConnection) CanWrite() (bool, error) {
	return true, nil
}

func (c *MyConnection) PWrite(buf []byte, offset uint64,
	flags uint32) error {
	copy(... to the data source here ..., buf)
	return nil
}

Editor note: In an earlier version of these bindings we passed the whole struct to each callback rather than a pointer, hence James’s first comment below.