nbdkit-vddk-plugin - Man Page

nbdkit VMware VDDK plugin

Synopsis

 nbdkit vddk [[file=]FILENAME | export=WILDCARD]
             [compression=none|zlib|fastlz|skipz]
             [config=FILENAME] [cookie=COOKIE]
             [create=true] [create-adapter-type=ide|scsi-buslogic|...]
             [create-hwversion=workstation4|workstation5|...]
             [create-size=...] [create-type=monolithic-sparse|...]
             [libdir=LIBRARY]
             [nfchostport=PORT] [single-link=true]
             [password=PASSWORD | password=- | password=+FILENAME |
              password=-FD]
             [port=PORT] [server=HOSTNAME] [snapshot=MOREF]
             [thumbprint=THUMBPRINT] [transports=MODE:MODE:...]
             [unbuffered=true] [user=USERNAME] [vm=moref=ID]
 nbdkit vddk --dump-plugin

Description

nbdkit-vddk-plugin is an nbdkit(1) plugin that serves disks from local VMware VMDK files, VMware ESXi servers, VMware VCenter servers, and other sources.

It requires VMware's proprietary VDDK library that you must download yourself (see "Library Location" below).

For an easy-to-use wrapper around this plugin which automates setting things up to connect to a remote VMware server, see: https://gitlab.com/nbdkit/vddk-remote

Examples

Open a local VMDK file

 $ nbdkit vddk libdir=/opt/vmware-vix-disklib-distrib \
               /absolute/path/to/file.vmdk
 $ nbdinfo --size nbd://localhost
 10485760
 $ nbdcopy nbd://localhost outputfile.raw

Open file.vmdk with this plugin, and use nbdinfo(1) and nbdcopy(1) to inspect and copy out the data. When opening local files the filename must be an absolute path.

The libdir parameter points to the location of VDDK, see "Library Location" below. In the examples below it is omitted for brevity.

You can use VDDK to create a VMDK file and fill it with the contents of a disk image. Note the create-size parameter is the virtual size of the final VMDK disk image and must be at least as large as the input disk:

 nbdkit vddk \
        /absolute/path/to/output.vmdk \
        create=true create-size=100M \
        --run 'qemu-img convert input.qcow2 $uri'

Open a file on a remote VMware ESXi hypervisor

Connect directly to a VMware ESXi hypervisor and export a particular file:

 nbdkit vddk user=root password=+/tmp/rootpw \
             server=esxi.example.com thumbprint=xx:xx:xx:... \
             vm=moref=2 \
             "[datastore1] Fedora/Fedora.vmdk"

user and password must be specified. Use password=+FILENAME to provide the password securely in a file.

server is the hostname of the ESXi server.

thumbprint is the thumb print for validating the SSL certificate. How to find the thumb print of a server is described in "Thumbprints" below.

vm is the Managed Object Reference ("moref") of the virtual machine. See "Managed Object Reference" below.

The file parameter is the file you want to open, usually in the form "[datastore] vmname/vmname.vmdk". See "File Parameter" below.

Open a file on a remote VMware vCenter server

Connect via VMware vCenter and export a particular file:

 nbdkit vddk user=root password=vmware \
             server=vcenter.example.com thumbprint=xx:xx:xx:... \
             vm=moref=vm-16 \
             "[datastore1] Fedora/Fedora.vmdk"

user and password must be specified. Use password=+FILENAME to provide the password securely in a file.

server is the hostname of the vCenter server.

thumbprint is the thumb print for validating the SSL certificate. How to find the thumb print of a server is described in "Thumbprints" below.

vm is the Managed Object Reference ("moref") of the virtual machine. See "Managed Object Reference" below.

The file parameter is the file you want to open, usually in the form "[datastore] vmname/vmname.vmdk". See "File Parameter" below.

Allow the client to choose the filename

As the previous example, but allow the client to choose which file to serve, using the export=WILDCARD parameter:

 nbdkit vddk user=root password=vmware \
             server=vcenter.example.com thumbprint=xx:xx:xx:... \
             vm=moref=vm-16 \
             export='\[datastore1\] Fedora/*.vmdk'

The client now picks the specific filename, as long as it matches the wildcard given on the nbdkit command line. For example:

 $ nbdsh
 nbd> h.set_export_name("[datastore1] Fedora/Fedora.vmdk")
 nbd> h.connect_tcp("localhost", "nbd")

or the same using an NBD URI with usual URL encoding:

 nbdinfo 'nbd://localhost/%5bdatastore1%5d%20Fedora/Fedora.vmdk'

Parameters

For opening a local VMDK file, the file parameter is required and must be an absolute path.

For opening a remote connection, server, thumbprint, user, password and vm are required. Either file or export are required.

All other parameters are optional.

compression=none

compression=zlib

compression=fastlz

compression=skipz

(nbdkit ≥ 1.24, vSphere ≥ 6.5)

Select the compression type used over the network between VDDK and the VMware server. The default is none. See VMware document “Best Practices for NBD Transport”.

config=FILENAME

The name of the VDDK configuration file.

The config file controls rarely adjusted VDDK settings like log level, caching and timeouts. See the VDDK documentation for a full list of settings.

VDDK itself looks in a few default locations for the configuration file, usually including /etc/vmware/config and $HOME/.vmware/config. Using config overrides these defaults.

cookie=COOKIE

(vSphere ≥ 6.7)

Cookie from existing authenticated session on the host.

This changes the authentication type from VIXDISKLIB_CRED_UID to VIXDISKLIB_CRED_SESSIONID which can improve performance. The cookie can be found by connecting to a VCenter Server over HTTPS and retrieving the vmware_soap_session cookie.

create=true

(nbdkit ≥ 1.30)

Create a new, local VMDK file. Instead of opening an existing VMDK file, a new VMDK file is created and opened. The filename is given by the file parameter (see below). The file must not exist already. It is not possible to create a remote file using nbdkit.

If this is used, the create-size parameter is required to specify the virtual size of the disk. Other create-* parameters (see below) can be used to control the VMDK sub-format.

create-adapter-type=ide

create-adapter-type=scsi-buslogic

create-adapter-type=scsi-lsilogic

(nbdkit ≥ 1.30)

Specify the VMDK disk adapter type. The default is scsi-buslogic.

create-hwversion=workstation4

create-hwversion=workstation5

create-hwversion=workstation6

create-hwversion=esx30

create-hwversion=esx4x

create-hwversion=esx50

create-hwversion=esx51

create-hwversion=esx55

create-hwversion=esx60

create-hwversion=esx65

create-hwversion=N

(nbdkit ≥ 1.30)

Specify the VMDK virtual hardware version. You can give either the named version or the equivalent 16 bit number.

The default is workstation5 (N = 4).

create-size=SIZE

(nbdkit ≥ 1.30)

Specify the virtual size of the created disk. The SIZE can use modifiers like 100M etc. It must be a multiple of 512 bytes because VMware only supports sector sizes.

If you use create=true then this parameter is required.

create-type=monolithic-sparse

create-type=monolithic-flat

create-type=split-sparse

create-type=split-flat

create-type=vmfs-flat

create-type=stream-optimized

create-type=vmfs-thin

create-type=vmfs-sparse

(nbdkit ≥ 1.30)

Specify the VMDK sub-format. The default is monolithic-sparse.

Some VMDK sub-formats use multiple files, where the file parameter specifies the "Disk Descriptor File" and the disk contents are stored in adjacent files.

export=WILDCARD

(nbdkit ≥ 1.44)

For remote connections, allow the client to choose which file to serve, using the NBD protocol export name. The export name must match WILDCARD. This is an alternative to specifying a single, exact filename, see file below.

[ and ] are special characters in wildcards and must be escaped as \[ and \]. In addition you may have to quote the whole wildcard to protect it from the shell.

The wildcard provides some security, but it is unwise to allow untrusted clients to connect when using this option.

[file=]FILENAME

[file=][datastore] vmname/vmname.vmdk

Set the name of the VMDK file to serve.

For local files you must supply an absolute path. For remote files see "File Parameter" section below.

file= prefix may be omitted in most cases. See "Magic parameters" in nbdkit(1).

libdir=PATHNAME

This sets the path of the VMware VDDK distribution.

VDDK uses this to load its own plugins, if this path is unspecified or wrong then VDDK will work with reduced functionality. See "Library Location" below.

nfchostport=PORT

Port used to establish an NFC connection to ESXi. Defaults to 902.

password=PASSWORD

Set the password to use when connecting to the remote server.

Note that passing this on the command line is not secure on shared machines.

password=-

Ask for the password (interactively) when nbdkit starts up.

password=+FILENAME

Read the password from the named file. This is a secure method to supply a password, as long as you set the permissions on the file appropriately.

password=-FD

Read the password from file descriptor number FD, inherited from the parent process when nbdkit starts up. This is also a secure method to supply a password.

port=PORT

The port on the VCenter/ESXi host. Defaults to 443.

server=HOSTNAME

The hostname or IP address of VCenter or ESXi host.

single-link=true

(nbdkit ≥ 1.12)

Open the current link, not the entire chain. This corresponds to the VIXDISKLIB_FLAG_OPEN_SINGLE_LINK flag.

snapshot=MOREF

The Managed Object Reference of the snapshot. See "Managed Object Reference" below.

thumbprint=THUMBPRINT

The SSL (SHA1) thumbprint for validating the SSL certificate.

The format is xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx (20 hex digit pairs).

See "Thumbprints" below for how to get this.

transports=MODE:MODE:...

List of one or more transport modes to use. Possible values include ‘nbd’, ‘nbdssl’, ‘san’, ‘hotadd’, ‘file’ (see "Dump-Plugin Output" below). If not given, VDDK will try to choose the best transport mode.

unbuffered=true

(nbdkit ≥ 1.12)

Disable host caching. This corresponds to the VIXDISKLIB_FLAG_OPEN_UNBUFFERED flag.

user=USERNAME

The username to connect to the remote server as.

vm=moref=ID

The Managed Object Reference ("moref") of the virtual machine. See "Managed Object Reference" below.

vimapiver=APIVER

This parameter is ignored for backwards compatibility.

Library Location

The VDDK library should not be placed on a system library path such as /usr/lib. The reason is that the VDDK library ships with recompiled libraries like libcrypto.so and libstdc++.so that conflict with system libraries.

You have two choices:

Place VDDK in the default libdir which is compiled into this plugin, for example:

 $ nbdkit vddk --dump-plugin | grep ^vddk_default_libdir
 vddk_default_libdir=/usr/lib64/vmware-vix-disklib

But the best advice is to unpack the VDDK tarball anywhere you like and set the libdir=/path/to/vmware-vix-disklib-distrib. For example:
```
 nbdkit vddk \
        libdir=/opt/vmware-vix-disklib-distrib \
        /path/to/file.vmdk
```

No need to set LD_LIBRARY_PATH

In nbdkit ≤ 1.16 you had to set the environment variable LD_LIBRARY_PATH when using this plugin. In nbdkit ≥ 1.18 this is not recommended.

Supported Versions of VDDK

VDDK ≥ 6.7 (released Apr 2018)

This is the minimum version of VDDK supported. Older versions will not work.

This is also the first version that supported the VixDiskLib_QueryAllocatedBlocks API. This is used to provide sparseness (extent) information over NBD.

VDDK 8.0.3 (released Jun 2024)

This is the latest version of VDDK that we have tested at the time of writing, but the plugin should work with future versions.

This plugin is only supported on the x86-64 architecture.

File Parameter

The file parameter can either be a local file, in which case it must be the absolute path. Or it can refer to a remote file on the VMware server in the format "[datastore] vmname/vmname.vmdk".

Finding the remote filename

For remote files you can find the path using virsh(1). For ESXi:

 $ virsh -c 'esx://esxi.example.com?no_verify=1' dumpxml guestname
 ...
  <disk type='file' device='disk'>
    <source file='[datastore] vmname/vmname.vmdk'/>
 ...

For vCenter the command is the same but the URI starts with vpx://:

 $ virsh -c 'vpx://vcenter.example.com/Datacenter/esxi.example.com?no_verify=1' \
         dumpxml guestname

Optional file= prefix

The file= part is optional, so these commands are equivalent:

 nbdkit vddk file=/path/to/file.vmdk
 nbdkit vddk /path/to/file.vmdk

Relationship to the export parameter

Instead of file, you can use the export=WILDCARD parameter to allow the client to choose the filename, as long as it matches the given wildcard.

Thumbprints

The thumbprint is a 20 byte string containing the SSL (SHA1) fingerprint of the remote VMware server and it is required when making a remote connection. There are several ways to obtain this.

Using a web browser

Visit https://SERVER-NAME/folder and log in. Click the lock icon next to the URL bar and navigate to the SHA-1 fingerprint of the site’s certificate. This 20 hex digit pair string can be directly copied to the thumbprint= parameter.

Using openssl remotely

The following command will print the thumbprint of a VMware server called SERVER-NAME:

 $ openssl s_client -connect SERVER-NAME:443 </dev/null |
   openssl x509 -in /dev/stdin -fingerprint -sha1 -noout

By logging in to the ESXi or vCenter server

 # openssl x509 -in /etc/vmware/ssl/rui.crt -fingerprint -sha1 -noout

For VMware vCenter servers the thumbprint is printed on the text console of the server or is available by logging in to the server and using this command:

 # openssl x509 -in /etc/vmware-vpx/ssl/rui.crt -fingerprint -sha1 -noout

Trick: Get VDDK to tell you the thumbprint

Another way to get the thumbprint of a server is to connect to the server using a bogus thumbprint with debugging enabled:

 nbdkit -fv vddk server=esxi.example.com [...] thumbprint=12 \
        --run 'qemu-img info "$uri"'

The nbdkit process will try to connect (and fail because the thumbprint is wrong). However in the debug output will be a message such as this:

 nbdkit: debug: VixDiskLibVim: Failed to verify SSL certificate: actual thumbprint=B2:31:BD:DE:9F:DB:9D:E0:78:EF:30:42:8A:41:B0:28:92:93:C8:DD expected=12

This gives you the server’s real thumbprint. Of course this method is not secure since it allows a Man-in-the-Middle (MITM) attack.

Managed Object Reference

Some use cases require you to pass in the Managed Object Reference ("moref") of an object on the VMware server.

For VMware ESXi hypervisors, the vm moref is a number (eg. vm=moref=2). For VMware VCenter it is a string beginning with "vm-") (eg. vm=moref=vm-16). Across ESXi and vCenter the numbers are different even for the same virtual machine.

If you have libvirt ≥ 3.7, the moref is available in the virsh(1) dumpxml output:

 $ virsh -c 'esx://esxi.example.com?no_verify=1' dumpxml guestname
 ...
 <vmware:moref>2</vmware:moref>
 ...

or:

 $ virsh -c 'vpx://vcenter.example.com/Datacenter/esxi.example.com?no_verify=1' \
       dumpxml guestname
 ...
 <vmware:moref>vm-16</vmware:moref>
 ...

An alternative way to find the moref of a VM is using the moRefFinder.pl script written by William Lam (http://www.virtuallyghetto.com/2011/11/vsphere-moref-managed-object-reference.html https://blogs.vmware.com/vsphere/2012/02/uniquely-identifying-virtual-machines-in-vsphere-and-vcloud-part-2-technical.html).

Dump-Plugin Output

To query more information about the plugin (and whether it is working), use:

 nbdkit vddk --dump-plugin

or:

 nbdkit vddk --dump-plugin libdir=/opt/vmware-vix-disklib-distrib

(see "Library Location" above).

If the plugin is not present or not working you will get an error.

If it works the output will include:

vddk_default_libdir=...

The compiled-in library path. Use libdir=PATHNAME to override this at runtime.

vddk_has_nfchostport=1

If this is printed then the nfchostport=PORT parameter is supported by this build.

vddk_library_version=...

The VDDK major library version: 6, 7, 8, ... If this is omitted it means the library could not be loaded.

vddk_dll=...

Prints the full path to the VDDK shared library. Since this requires a glibc extension it may not be available in all builds of the plugin.

vddk_transport_modes=...

Print the list of transport modes supported by VDDK. This is a colon-separated list such as file:san:hotadd:nbdssl:nbd

This is the default set of transport modes that are tried in turn, unless you override the list using the transports=... parameter.

VixDiskLib_...=1

For each VDDK API that the plugin uses and which is present in the VDDK library that was loaded, we print the name of the API (eg. VixDiskLib_Open=1). This lets you see which optional APIs are available, such as VixDiskLib_Flush and VixDiskLib_QueryAllocatedBlocks. If the library could not be loaded then these lines are not printed.

Notes

Sector size limitation

The VDDK plugin can only answer read/write requests on whole 512 byte sector boundaries. This is because the VDDK Read and Write APIs only take sector numbers. If your client needs finer granularity, you can use nbdkit-blocksize-filter(1):

 nbdkit vddk ... --filter=blocksize minblock=512

FileLockCreateEntryDirectory errors

When opening a local VMDK file, VDDK needs to create a lock file in the same directory. The directory must be writable otherwise you will see errors like:

 nbdkit: vddk[1]: error: FILE: FileLockCreateEntryDirectory creation
 failure on '/absolute/path/to/file.vmdk.lck': Permission denied

The solution is to either make the directory / filesystem writable; or open the file read-only by adding the nbdkit -r option:

 nbdkit -r vddk /absolute/path/to/file.vmdk

Out of memory errors

In the verbose log you may see errors like:

 nbdkit: vddk[3]: error: [NFC ERROR] NfcFssrvrProcessErrorMsg:
 received NFC error 5 from server: Failed to allocate the
 requested 2097176 bytes

This seems especially common when there are multiple parallel connections open to the VMware server with large NBD reads and writes.

Increase resource limits on the server

The error above can be caused by resource limits set on the VMware server. You can increase the limit for the NFC service by editing /etc/vmware/hostd/config.xml and adjusting the <maxMemory> setting:

 <nfcsvc>
   <path>libnfcsvc.so</path>
   <enabled>true</enabled>
   <maxMemory>50331648</maxMemory>
   <maxStreamMemory>10485760</maxStreamMemory>
 </nfcsvc>

and restarting the hostd service:

 # /etc/init.d/hostd restart

For more information see https://bugzilla.redhat.com/1614276.

Limit request sizes

In addition, or as an alternative to adjusting the server configuration, you can use nbdkit-blocksize-filter(1) to limit the maximum request size. By default this plugin translates NBD requests directly into VDDK requests, and it appears that very large VDDK requests can cause the error seen above.

Using:

 nbdkit vddk ... --filter=blocksize minblock=512 maxdata=2M

will cause nbdkit to automatically split and combine requests so that VDDK sees only sizes in the range [512..2M].

Error 1 (Unknown error) when opening a disk

Opening a disk fails with an error like:

 nbdkit: vddk[1]: debug: VixDiskLib: VixDiskLib_OpenEx:
 Cannot open disk <name>. Error 1 (Unknown error) at <line>.

This common and totally useless error message can be printed by VDDK for lots of reasons. Make sure debugging is enabled and look at any debug messages printed before this to find out what is really going on. Common reasons are listed below.

The thumbprint parameter is wrong

Verify whether the thumbprint parameter matches the SHA1 fingerprint of the remote VMware server. See "Thumbprints" above for how to set this correctly.

The guest is using an "Independent" mode disk

In debugging output you will see messages including:

 GetFileName: Cannot create disk spec for disk <name>.
 Error occurred when obtaining the file name for <name>.

If the Disk Mode is "Independent-Persistent" or "Independent-Nonpersistent", then VDDK ≥ 7 has a bug where it cannot open these disks. The only known workarounds are to use VDDK ≤ 6.7, or to change the Disk Mode to a regular dependent disk.

Troubleshooting performance problems

VDDK has very uneven performance with some operations being very slow. This plugin has options to allow you to debug performance issues. If your application has a debug or diagnostic setting, add the following nbdkit command line options:

 -v -D nbdkit.backend.datapath=0 -D vddk.datapath=0 -D vddk.stats=1

-v enables verbose messages and the two datapath options disable the very verbose per-read/-write messages. -D vddk.stats=1 enables a summary when nbdkit exits of the cumulative time taken in each VDDK function, the number of times each function was called, and (for read and write) the number of bytes transferred. An example of what those stats look like can be found here: https://gitlab.com/nbdkit/nbdkit/-/commit/5c80f0d290db45a679d55baf37ff39bacb8ce7ec

You can interpret the stats as follows:

Read: The cumulative time spent waiting for VDDK to return from VixDiskLib_Read calls, the number of times this function was called, and the total bytes read. You can use this to determine the read bandwidth to the VMware server.
Write
Flush: Same as above, but for writing and flushing writes.
ReadAsync
WriteAsync: Same as above, but for asynchronous read and write calls introduced in nbdkit 1.30. Unfortunately at the moment the amount of time spent in these calls is not accounted for correctly.
QueryAllocatedBlocks: This call is used to query information about the sparseness of the remote disk. It is only available in VDDK ≥ 6.7. The call is notably very slow in all versions of VMware we have tested.
Open
Close
ConnectEx
Disconnect
InitEx
Exit: The cumulative time spent connecting and disconnecting from the VMware server, which can also be very slow.

Failure to load libssl.so.3 on RHEL 8

With VDDK ≥ 8.0.2 on Red Hat Enterprise Linux 8:

 nbdkit: error: libssl.so.3: cannot open shared object file:
 No such file or directory

This is a bug in VDDK. The workaround is to use VDDK 8.0.1. See also: https://issues.redhat.com/browse/RHEL-28533

Debug Flags

Debugging messages can be very helpful if you have problems connecting to VMware servers, or to find the list of available transport modes, or to diagnose SAN problems:

 nbdkit -f -v vddk file=FILENAME [...]

Additional debug flags are available:

-D vddk.diskinfo=1: Debug disk information returned by GetInfo.
-D vddk.extents=1: Debug extents returned by QueryAllocatedBlocks.
-D vddk.datapath=0: Suppress debugging of datapath calls (Read, ReadAsync, Write and WriteAsync).
-D vddk.stats=1: When the plugin exits print some statistics about each VDDK call.

Files

$plugindir/nbdkit-vddk-plugin.so

The plugin.

Use nbdkit --dump-config to find the location of $plugindir.

Version

nbdkit-vddk-plugin first appeared in nbdkit 1.2.

Authors

Richard W.M. Jones

Copyright

License

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
Neither the name of Red Hat nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

nbdkit-vddk-plugin - Man Page

Synopsis

Description

Examples

Open a local VMDK file

Create a new local VMDK file

Open a file on a remote VMware ESXi hypervisor

Open a file on a remote VMware vCenter server

Allow the client to choose the filename

Parameters

Library Location

No need to set LD_LIBRARY_PATH

Supported Versions of VDDK

File Parameter

Finding the remote filename

Optional file= prefix

Relationship to the export parameter

Thumbprints

Using a web browser

Using openssl remotely

By logging in to the ESXi or vCenter server

Trick: Get VDDK to tell you the thumbprint

Managed Object Reference

Dump-Plugin Output

Notes

Sector size limitation

FileLockCreateEntryDirectory errors

Out of memory errors

Error 1 (Unknown error) when opening a disk

Troubleshooting performance problems

Failure to load libssl.so.3 on RHEL 8

Debug Flags

Files

Version

See Also

Authors

Copyright

License

Referenced By