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nbdkit is an NBD server.  NBD — Network Block Device — is a protocol
for accessing Block Devices (hard disks and disk-like things) over a
Network.

The key features of nbdkit are:

 * Multithreaded NBD server written in C with good performance.

 * Minimal dependencies for the basic server.

 * Liberal license (BSD) allows nbdkit to be linked to proprietary
   libraries or included in proprietary code.

 * Well-documented, simple plugin API with a stable ABI guarantee.
   Lets you export “unconventional” block devices easily.

 * You can write plugins in C/C++, Go, Lua, Perl, Python, OCaml, Ruby,
   Rust, shell script or Tcl.

 * Filters can be stacked in front of plugins to transform the output.

For documentation, see the ‘docs/’ directory.

For plugins and filters, see the ‘plugins/’ and ‘filters/’
directories.  Example plugins can be found in ‘plugins/example*’.

There are many NBD clients, but the nbdkit project has a companion
client library called https://gitlab.com/nbdkit/libnbd

https://gitlab.com/nbdkit/nbdkit

LICENSE
=======

This software is copyright (C) Red Hat Inc. and licensed under a BSD
license.  See ‘LICENSE’ for details.

BUILDING FROM SOURCE
====================

Requirements
------------

 - Linux, FreeBSD, OpenBSD or Haiku

 - GCC or Clang

 - bash

 - GNU make

Recommended for TLS (authentication and encryption) support, but it is
possible to build without it:

 - gnutls >= 3.3.0

nbdkit also works on Windows, but dependencies are more complicated.
See the separate section at the end of this document.

Optional dependencies
---------------------

To build the man pages, you will optionally need to install:

 - Perl

 - Pod::Man and Pod::Simple (Perl libraries)

For SELinux socket labelling support:

 - libselinux

For the gzip filter:

 - zlib

For the xz filter:

 - liblzma

For the memory plugin with allocator=zstd:

 - zstd

For the curl (HTTP/FTP) plugin:

 - libcurl

For the ssh plugin:

 - libssh >= 0.8.0
   (this is a different library from libssh2 - that will not work)

For the iso plugin:

 - xorriso or genisoimage or mkisofs

For the floppy plugin:

 - iconv (on Linux this is built into glibc, on other systems
   it may be a separate library)

For the libvirt plugin:

 - libvirt

For the libguestfs plugin, and to run parts of the test suite:

 - libguestfs

 - guestfish (from libguestfs)

For the ext2 filter:

 - ext2fs

 - com_err

For the linuxdisk plugin:

 - mke2fs >= 1.42.10 (from e2fsprogs)

For the nbd plugin, to get URI and TLS support, and also to run parts
of the test suite:

 - libnbd >= 0.9.8

For the bittorrent plugin:

 - libtorrent-rasterbar (https://www.libtorrent.org)

For the containerized data importer (CDI) plugin:

 - podman

 - jq

For the Perl and example4 plugins:

 - perl interpreter

 - perl development libraries

 - perl modules ExtUtils::Embed

For the Python plugin:

 - python interpreter (version 3 only)

 - python development libraries

 - python unittest to run the test suite

 - boto3 is required to run the S3 plugin written in Python

For the OCaml plugin:

 - OCaml >= 4.03

For the Tcl plugin:

 - Tcl development library and headers

For the Lua plugin:

 - Lua development library and headers

For the Rust plugin:

 - cargo (other dependencies will be downloaded at build time)

To be able to write plugins in golang:

 - go >= 1.13

For bash tab completion:

 - bash-completion >= 1.99

To test for memory leaks (‘make check-valgrind’):

 - valgrind program and development headers

For non-essential enhancements to the test suite:

 - expect

 - flake8

 - hexdump

 - ip, ss (from iproute package)

 - jq

 - losetup (from util-linux package)

 - mke2fs (from e2fsprogs)

 - nbdcopy, nbdsh (from libnbd)

 - qemu-img, qemu-io, qemu-nbd (usually shipped with qemu)

 - sfdisk (from util-linux)

 - socat

 - ssh-keygen

 - stat (from coreutils)

Building
--------

    To build from tarball:         To build from git:
    ----------------------         ------------------
                                   autoreconf -i
    ./configure                    ./configure
    make                           make
    make check                     make check

To run nbdkit from the source directory, use the top level ./nbdkit
wrapper.  It will run nbdkit and plugins from the locally compiled
directory:

    $ ./nbdkit example1 -f -v
    ./server/nbdkit ./plugins/example1/.libs/nbdkit-example1-plugin.so -f -v
    [etc]

Optionally run this command as root to install everything:

    make install

Python
------

Since nbdkit >= 1.16, only Python >= 3.6 is supported.

By default nbdkit uses the Python version of the Python interpreter
called “python” on the current $PATH.  If you have parallel versions
of Python installed then you can choose a different version by setting
the PYTHON variable when configuring.  For example:

    ./configure PYTHON=/usr/bin/python3.8

OCaml
-----

Most recent (less than, say, 8 years old) versions of the OCaml
compiler should work.  By default the configure script should detect
the bytecode and native code compilers and enable either one or both.

To enable OCaml warnings and turn them into hard errors (developers only):

    ./configure OCAMLOPTFLAGS="-warn-error +A-3"

Running the tests
-----------------

To run the test suite:

    make check

If there is a failure, look at the corresponding ‘tests/*.log’ file
for debug information.

A few tests require root privileges, and are skipped by default.  To
run them you must do:

    sudo make check-root

If you have the proprietary VDDK library, you can test
nbdkit-vddk-plugin against the library like this:

    make check-vddk vddkdir=vmware-vix-disklib-distrib

Running the benchmarks
----------------------

To run benchmarks:

    make bench

DOWNLOAD TARBALLS
=================

Tarballs are available from:
http://libguestfs.org/download/nbdkit

DOWNSTREAM PACKAGERS
====================

If you are packaging nbdkit, use:

    ./configure --with-extra='...'

providing extra information about the distribution, and/or
distro-specific versions.  It helps us with troubleshooting bug
reports.  (Also, talk to us!)

DEVELOPERS
==========

Install the valgrind program and development headers.

Use:

    ./configure --enable-gcc-warnings --enable-valgrind

When testing use:

    make check
    make check-valgrind

For development ideas, see the TODO file.

The upstream git repository is:
https://gitlab.com/nbdkit/nbdkit

Please send patches to the libguestfs mailing list:
https://www.redhat.com/mailman/listinfo/libguestfs

For further information, see:
https://libguestfs.org/
https://github.com/NetworkBlockDevice/nbd/blob/master/doc/proto.md

Test coverage
-------------

    ./configure CFLAGS="--coverage -g" LDFLAGS="--coverage -g"
    make clean
    make
    make check

    lcov -c -d . -o gcov.info
    genhtml -o coverage gcov.info

Open your browser and examine the coverage/ directory.  At the time of
writing (2020-04) test coverage of the server is reasonable, but
things are much worse for certain plugins and filters.

WINDOWS
=======

Experimentally, the server can be compiled on Windows or
cross-compiled from Linux using mingw-w64.  Only a small subset of
features are available.  To find out what is missing read the TODO
"Windows port".

Note that GCC or Clang is required even if you are compiling on
Windows because of some C language extensions we use.  MSVC will not
work.

Cross-compiling from Linux to Windows
-------------------------------------

For the rest of this section we talk about cross-compiling for Windows
using Linux and mingw-w64.  At a minimum you will need:

    mingw-w64 GCC
    mingw-w64 dlfcn
    mingw-w64 winpthreads
    mingw-w64 gnutls  (optional, but highly recommended)
    wine              (if you want to run it on Linux)

You may want to patch Wine with this patch which adds support for
AF_UNIX sockets.  It is needed to get most of the test suite to work,
but if you don't care about the -U option then it is not needed.
https://www.winehq.org/pipermail/wine-devel/2021-May/187049.html

Other mingw-w64 libraries may be installed which will add
functionality (see full list of requirements above), but you may end
up hitting areas we have not compiled or tested before.

To cross compile do:

    mingw64-configure --disable-ocaml --disable-perl --disable-vddk
    mingw64-make

You can test if the server is working by doing:

    ./nbdkit.exe --dump-config

(This usually runs wine automatically.  If not, you may need to prefix
the command "wine nbdkit.exe ...")

To see which plugins and filters were compiled:

    find plugins filters -name '*.dll'

You can run them under Wine without installing using eg:

    ./nbdkit.exe -f -v memory 1G

You can run the test suite in the usual way:

    mingw64-make check

Running the cross-compiled binary on Windows
--------------------------------------------

To test the binary on a real Windows system you will need to copy
server/.libs/nbdkit.exe, any plugins and filters you need
(plugins/*/.libs/*.dll and filters/*/.libs/*.dll), and many mingw DLLs
(libdl.dll, libgnutls.dll, libwinpthread.dll, etc.).

Notes:

(1) libtool creates files called nbdkit.exe in the top level directory
and in server/.  These are the stripped binaries.  The "real" binaries
are located in hidden .libs/ subdirectories.

(2) The top level .libs/nbdkit.exe is the wrapper used to run nbdkit
from the build directory, not the server binary.  You need
server/.libs/nbdkit.exe instead.

(3) To find the list of mingw DLLs I ran nbdkit.exe iteratively until
Windows stopped complaining about missing libraries.  You could also
use a tool like Dependency Walker.

If you copy everything into a single directory on the Windows server
then you should be able to run nbdkit normally, eg:

    nbdkit.exe -f -v nbdkit-memory-plugin.dll 1G

You will probably need to open port 10809 on the Windows Firewall.