gonbdserver

gonbdserver is an NBD server written in Go. Its purpose is not to be especially performant, but rather to act as a simple demonstration of the implementation of the NBD protocol. That said, where tested it appears to be at least as fast as the reference nbdserver implementation.

Features

• Wide protocol support. Supports both FLUSH and FUA.

• Multithreaded. Defaults to 5 worker threads per connection, so able to process requests in parallel.

• TLS support. With client certificates if required.

• Ceph RBD support. Almost entirely untested.

• Linux AIO support. Experimental.

• Pluggable backends. By default a file backend is provided, as well as a Ceph/RBD backend on linux, but it would be possible to supply any backend. The ceph driver is there mostly to illustrate just how easy this is.

• Reloadable configuration. It is possible to reload the configuration using SIGHUP without affecting existing servers.

• Newstyle negotiation (only). Oldstyle negotiation is not supported. This is a feature, not a bug.

• Logging. To syslog, a file, or stderr

NBD Experimental Extensions Implemented

• WRITE_ZEROES - support for NBD_CMD_WRITE_ZEROES

• INFO - support for NBD_OPT_INFO, NBD_OPT_GO and NBD_OPT_BLOCK_SIZE.

Invocation

Invocation is very easy. It takes a minimum number of command-line flags. Most of the configuration is within the configuration file.

$ ./gonbdserver --help
Usage of ./gonbdserver:
  -c string
    	Path to YAML config file (default "/etc/gonbdserver.conf")
  -f	Run in foreground (not as daemon)
  -p string
    	Path to PID file (default "/var/run/gonbdserver.pid")
  -s string
    	Send signal to daemon (either "stop" or "reload")

By default gonbdserver runs as a daemon. You can use -f to make it run in the foreground. If you are running on Linux and want to run from init, you may wish to consider using start-stop-daemon with the -b flag, and invoking gondbserver with the -f flag, as start-stop-daemon is probably better at dealing with the many possible failure modes.

When running in foreground mode, the pid file is not used, and -s is irrelevant.

Note that to use the -s option, it is necessary to specify the -c and -p options that you used in launching the daemon.

Signals

• SIGHUP (or gonbdserver -s reload) will cleanly reload the configuration. Existing connections to the server will be unaffected (i.e. they will run with the previous configuration) until a disconnect / reconnect occurs.

• SIGTERM (or gonbdserver -s stop) will cleanly terminate the daemon. Existing connections to the server will be terminated.

Configuration

Configuration is provided through a YAML file which by default lives at /etc/gonbdserver.conf, though this can be specified using the -c option.

An example of a configuration is set out below:

servers:
- protocol: tcp                  # A first server, using TCP
  address: 127.0.0.1:6666        # on port 6666
  exports:                       # It has two exports
  - name: foo                    # The first is named 'foo' and
    driver: file                 # Uses the 'file' driver
    path: /tmp/test              # This uses /tmp/test as the file
    workers: 4                   # Use 4 workers
  - name: bar                    # The second export is called 'bar'
    readonly: true               # This is readonly
    driver: rbd                  # And uses the (currently imaginary) rbd driver
    image: rbdbar                # on this rados block device name
    tlsonly: true                # require TLS on this device
  tls:                           # use the following certificates
    keyfile: /path/to/server-key.pem
    certfile: /path/to/server-cert.pem
    cacertfile: /path/to/ca-cert.pem
    servername: foo.example.com  # present the server name as 'foo.example.com'
    clientauth: requireverify    # require and verify client certificates
- protocol: unix                 # Another server uses UNIX
  address: /var/run/nbd.sock     # served on this socket
  exports:                       # it has one export
  - name: baz                    # named bar
    driver: file                 # using the file driver
    path: /tmp/baz               # on this file
    sync: true                   # open with O_SYNC
  disablenozeroes: true          # disable nozereos for back compatibility
logging:                         # log to
  syslogfacility: local1         # local1

A description of the configuration file's sections is set out below

Top level

The top level of the configuration file consists of the following sections:

• servers: A list of zero or more server items
• logging: A logging item (optional)

server items

Each server item specifies a TCP port or unix socket that is listened to for new connections.

Each server item consists of the following:

• protocol: a description of the protocol it should listen. Valid values are tcp, tcp4 (TCP on IPv4 only), tcp6 (TCP on IPv6 ony), or unix. Optional, defaults to tcp.
• address: the address to listen on. For TCP protocols, this takes the form address:port in the normal manner. For UNIX protocols, this is the path to a Unix domain socket. Mandatory.
• exports: a list of zero or more export items each representing an export to be served by this server. This section is optional (and can be empty), but the server will be of little use if so.
• defaultexport: the name of the default export, which should be selected if no name is specified by the client. Optional, defaults to none.
• tls: a TLS item
• disablenozeroes:: disable NBD_FLAG_NO_ZEROES for back compatibility with nbd client prior to 3.10, where in error this was sent to the kernel as a 'read-only' flag. Optional, defaults to false.

export items

Each export item represents an export (i.e. an NBD disk) to be served by the server. Each export is served by a driver, and the drivers parameters (which are specific to the driver) may be intermingled with the export parameters.

Each export item consists of the following (common to all drivers):

• name: the name of the export as served over NBD. Mandatory.
• description: the human readable description of the export. Optional, defaults to an empty string.
• driver: the driver. Currently valid drivers are: file. Mandatory.
• readonly: set to true for readonly, false otherwise. Optional, defaults to false.
• workers: the number of simultaneous worker threads. Optional, defaults to 5.
• tlsonly: set to true if the export is only to be provided over TLS, false otherwise. Optional, defaults to false
• minimumblocksize: set to the minimum block size (must be a power of two). Optional, defaults to driver's minimum block size
• preferredblocksize: set to the preferred block size (must be a power of two). Optional, defaults to driver's preferred block size
• maximumblocksize: set to the maximum block size (must be a multiple of preferredblocksize). Optional, defaults to driver's maximum block size
• flush: set to true to forcibly enable support of the flush command, even if the driver does not support it; set to false to forcibly disable support for the flush command, even if the driver does support it. Optional, defaults to unset (i.e. use the driver's own setting)
• fua: set to true to forcibly enable support of the FUA (force unit access) flag, even if the driver does not support it; set to false to forcibly disable support for the FUA flag, even if the driver does support it. Optional, defaults to unset (i.e. use the driver's own setting)

The file driver reads the disk from a file on the host OS's disks. It has the following options:

• path: path to the file. Mandatory.
• sync: set to true to open the file with O_SYNC, else to false. Optional, defaults to false.

The aiofile driver reads the disk from a file on the host OS's disks using AIO (available on Linux only). This driver is experimental; do not use it in production. It has the following options:

• path: path to the file. Mandatory.
• sync: set to true to open the file with O_SYNC, else to false. Optional, defaults to false.

The rbd driver reads the disk from Ceph. It relies on your ceph.conf file being set up correctly, and has the following options:

• image: RBD name of image. Mandatory.
• pool: RBD pool for image. Optional, defaults to rbd.
• cluster: ceph cluster name. Defaults to ceph.
• user: ceph user name. Defaults to client.admin.

Note the Ceph driver is almost entirely untested

tls item

The tls item is used to enable TLS encryption on a server. If TLS is enabled on a server, the exports will be available over TLS. To make individual exports available only over TLS, add tlsonly: true to the export

• keyfile: Path to TLS key file in PEM format. Mandatory.
• certfile: Path to TLS cert file in PEM format. Optional, if not provided, defaults to KeyFile and assumes the PEM at keyfile has the certificate in as well as the private key.
• servername: Server name as announced by TLS. Optional, if not provided defaults to host name.
• cacertfile: Path to a file containing one or more CA certificates in PEM format. Optional, but required if validating client certificates
• clientauth: Client authentication strategy. Optional, defaulting to none. Must be one of the following values: none (no client certificate is requested or verified), request (a client certificate is requested but not verified), require (a client certificate is requested and required, but not verified), verify (a client certificate is requested and if provided is verified), or requireverify (a client certificate is requested and required, then verified)
• minversion: minimum TLS version. Optional, defaults to no minimum version. Must be one of the following values: ssl3.0, tls1.0, tls1.1 or tls1.2.
• maxversion: maximum TLS version. Optional, defaults to no maximum version. Must be one of the following values: ssl3.0, tls1.0, tls1.1 or tls1.2.

logging item

The logging item controls logging. There are three types of logging supported:

• Logging to stderr (the default)
• Logging to a file
• Logging to syslog

The logging item consists of the following:

• File: a the path to a file to log to. Optional. If not specified, will not log to a file. May not be specified together with SyslogFacility.
• FileMode: the permission mode (in octal) used to create the file. Optional. Defaults to 0644.
• SyslogFacility: the name of a syslog facility. Optional. If not specified, will not log to syslog. May not be specified together with File:.
• Date: set to true to log the date, else set to false. Optional. Defaults to false. Note if logging to syslog, your syslog daemon may add the date anyway.
• Time: set to true to log the time, else set to false. Optional. Defaults to false. Note if logging to syslog, your syslog daemon may add the time anyway.
• Microseconds: set to true to log the time in microseconds, else set to false. Optional. Defaults to false. Note if logging to syslog, your syslog daemon may add the time anyway.
• UTC: set to true to log the time in UTC, else set to false. Optional. Defaults to false. Note if logging to syslog, your syslog daemon may add the time anyway.
• SourceFile: set to true to log the source file emitting the log message, else set to false. Optional. Defaults to false.

Licence

The code is licensed under the MIT licence.