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.\" ========================================================================
.\"
.IX Title "nbdkit-file-plugin 1"
.TH nbdkit-file-plugin 1 "2021-01-20" "nbdkit-1.24.1" "NBDKIT"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
nbdkit\-file\-plugin \- nbdkit file plugin
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\& nbdkit file [file=]FILENAME
\&             [cache=default|none] [fadvise=normal|random|sequential]
\&
\& nbdkit file dir=DIRNAME
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\f(CW\*(C`nbdkit\-file\-plugin\*(C'\fR is a file serving plugin for \fBnbdkit\fR\|(1).
.PP
It serves the named \f(CW\*(C`FILENAME\*(C'\fR over \s-1NBD.\s0  Local block devices
(eg. \fI/dev/sda\fR) may also be served.  It may also be used to serve
any file within a given \f(CW\*(C`DIRECTORY\*(C'\fR, according to which export name
the guest requests.
.SH "PARAMETERS"
.IX Header "PARAMETERS"
One of \fBfile\fR or \fBdir\fR must be given to determine which mode
the server will use.
.IP "\fBcache=default\fR" 4
.IX Item "cache=default"
.PD 0
.IP "\fBcache=none\fR" 4
.IX Item "cache=none"
.PD
(nbdkit ≥ 1.22, not Windows)
.Sp
Using \f(CW\*(C`cache=none\*(C'\fR tries to prevent the kernel from keeping parts of
the file that have already been read or written in the page cache.
.IP "\fBfadvise=normal\fR" 4
.IX Item "fadvise=normal"
.PD 0
.IP "\fBfadvise=random\fR" 4
.IX Item "fadvise=random"
.IP "\fBfadvise=sequential\fR" 4
.IX Item "fadvise=sequential"
.PD
(nbdkit ≥ 1.22, not Windows)
.Sp
This optional flag hints to the kernel that you will access the file
normally, or in a random order, or sequentially.  The exact behaviour
depends on your operating system, but for Linux using \f(CW\*(C`normal\*(C'\fR causes
the kernel to read-ahead, \f(CW\*(C`sequential\*(C'\fR causes the kernel to
read-ahead twice as much as \f(CW\*(C`normal\*(C'\fR, and \f(CW\*(C`random\*(C'\fR turns off
read-ahead.  See also \fBposix_fadvise\fR\|(2).
.Sp
The default is \f(CW\*(C`normal\*(C'\fR.
.IP "[\fBfile=\fR]FILENAME" 4
.IX Item "[file=]FILENAME"
Serve the file named \f(CW\*(C`FILENAME\*(C'\fR.  A local block device name can also
be used here.  When this mode is used, the export name requested by
the client is ignored.
.Sp
\&\f(CW\*(C`file=\*(C'\fR is a magic config key and may be omitted in most cases.
See \*(L"Magic parameters\*(R" in \fBnbdkit\fR\|(1).
.IP "[\fBfile=\fR]\fB\e\e.\e\fRC\fB:\fR" 4
.IX Item "[file=].C:"
.PD 0
.IP "[\fBfile=\fR]\fB\e\e.\e\fRVolume" 4
.IX Item "[file=].Volume"
.IP "[\fBfile=\fR]\fB\e\e.\ePhysicalDisk\fR\fIN\fR" 4
.IX Item "[file=].PhysicalDiskN"
.IP "[\fBfile=\fR]\fB\e\e.\eCdRom\fR\fIN\fR" 4
.IX Item "[file=].CdRomN"
.PD
(Windows only)
.Sp
Serve the Windows volume specified by the device name.  See:
https://docs.microsoft.com/en\-us/windows/win32/fileio/naming\-a\-file#win32\-device\-namespaces.
.IP "\fBdir=\fR\s-1DIRNAME\s0" 4
.IX Item "dir=DIRNAME"
(nbdkit ≥ 1.22, not Windows)
.Sp
Serve all regular files and block devices located directly within the
directory named \f(CW\*(C`DIRNAME\*(C'\fR, including those found by following
symbolic links.  Other special files in the directory (such as
subdirectories, fifos, or Unix sockets) are ignored.  When this mode
is used, the file to be served is chosen by the export name passed by
the client, where the client can request a list of available exports
using \s-1NBD_OPT_LIST.\s0  A client that requests the default export (\f(CW""\fR)
will be rejected.  However, you can use \fBnbdkit\-exportname\-filter\fR\|(1)
to adjust what export names the client sees or uses as a default.  For
security, when using directory mode, this plugin will not accept
export names containing slash (\f(CW\*(C`/\*(C'\fR).
.SH "NOTES"
.IX Header "NOTES"
.SS "Optimizing for random or sequential access"
.IX Subsection "Optimizing for random or sequential access"
If you know in advance that the \s-1NBD\s0 client will access the file
randomly or only sequentially then you can hint that to the kernel
using:
.PP
.Vb 2
\& nbdkit file disk.img fadvise=random
\& nbdkit file disk.img fadvise=sequential
.Ve
.PP
As described in the \*(L"\s-1PARAMETERS\*(R"\s0 section above, on Linux this
disables or increases the amount of read-ahead that the kernel does.
.SS "Reducing evictions from the page cache"
.IX Subsection "Reducing evictions from the page cache"
If the file is very large and you know the client will only read/write
the file sequentially one time (eg for making a single copy or backup)
then this will stop other processes from being evicted from the page
cache:
.PP
.Vb 1
\& nbdkit file disk.img fadvise=sequential cache=none
.Ve
.SS "Files on tmpfs"
.IX Subsection "Files on tmpfs"
If you want to expose a file that resides on a file system known to
have poor \f(CWlseek(2)\fR performance when searching for holes (\f(CW\*(C`tmpfs\*(C'\fR
is known to be one such file system), you can use
\&\fBnbdkit\-noextents\-filter\fR\|(1) to avoid the penalty of probing for
holes.
.SS "Plugin \fI\-\-dump\-plugin\fP output"
.IX Subsection "Plugin --dump-plugin output"
You can obtain extra information about how the file plugin was
compiled by doing:
.PP
.Vb 1
\& nbdkit file \-\-dump\-plugin
.Ve
.PP
Some of the fields which may appear are listed below.  Note these are
for information only and may be changed or removed at any time in the
future.
.ie n .IP """file_blksszget=yes""" 4
.el .IP "\f(CWfile_blksszget=yes\fR" 4
.IX Item "file_blksszget=yes"
.PD 0
.ie n .IP """file_blkzeroout=yes""" 4
.el .IP "\f(CWfile_blkzeroout=yes\fR" 4
.IX Item "file_blkzeroout=yes"
.PD
If both set, the plugin may be able to efficiently zero ranges of
block devices, where the driver and block device itself supports this.
.ie n .IP """file_falloc_fl_punch_hole=yes""" 4
.el .IP "\f(CWfile_falloc_fl_punch_hole=yes\fR" 4
.IX Item "file_falloc_fl_punch_hole=yes"
If set, the plugin may be able to punch holes (make sparse) files and
block devices.
.ie n .IP """file_falloc_fl_zero_range=yes""" 4
.el .IP "\f(CWfile_falloc_fl_zero_range=yes\fR" 4
.IX Item "file_falloc_fl_zero_range=yes"
If set, the plugin may be able to efficiently zero ranges of files and
block devices.
.ie n .IP """winfile=yes""" 4
.el .IP "\f(CWwinfile=yes\fR" 4
.IX Item "winfile=yes"
If present, this is the Windows version of the file plugin which lacks
certain features as noted in this manual.
.SS "Windows sparse files"
.IX Subsection "Windows sparse files"
This plugin supports sparse files on Windows (with hole punching).
However for this to work the files must already have the sparse
property, the plugin will not make existing files sparse.  Use the
\&\f(CW\*(C`fsutil sparse\*(C'\fR command to control the sparseness property of
files.
.ie n .SS "Old ""rdelay"" and ""wdelay"" parameters."
.el .SS "Old \f(CWrdelay\fP and \f(CWwdelay\fP parameters."
.IX Subsection "Old rdelay and wdelay parameters."
Before nbdkit supported filters (< 1.2) this plugin had extra
parameters \f(CW\*(C`rdelay\*(C'\fR and \f(CW\*(C`wdelay\*(C'\fR to insert delays.  These parameters
have been moved to \fBnbdkit\-delay\-filter\fR\|(1).  Modify the command line
to add \fI\-\-filter=delay\fR in order to use these parameters.
.SS "Concatenating files"
.IX Subsection "Concatenating files"
To concatenate and export multiple files, use
\&\fBnbdkit\-split\-plugin\fR\|(1).
.SH "DEBUG FLAG"
.IX Header "DEBUG FLAG"
.IP "\fB\-D file.zero=1\fR" 4
.IX Item "-D file.zero=1"
This enables very verbose debugging of the \s-1NBD\s0 zero request.  This can
be used to tell if the file plugin is able to zero ranges in the file
or block device efficiently or not.
.SH "FILES"
.IX Header "FILES"
.IP "\fI\f(CI$plugindir\fI/nbdkit\-file\-plugin.so\fR" 4
.IX Item "$plugindir/nbdkit-file-plugin.so"
The plugin.
.Sp
Use \f(CW\*(C`nbdkit \-\-dump\-config\*(C'\fR to find the location of \f(CW$plugindir\fR.
.SH "VERSION"
.IX Header "VERSION"
\&\f(CW\*(C`nbdkit\-file\-plugin\*(C'\fR first appeared in nbdkit 1.0.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBnbdkit\fR\|(1),
\&\fBnbdkit\-plugin\fR\|(3),
\&\fBnbdkit\-split\-plugin\fR\|(1),
\&\fBnbdkit\-partitioning\-plugin\fR\|(1),
\&\fBnbdkit\-tmpdisk\-plugin\fR\|(1),
\&\fBnbdkit\-exportname\-filter\fR\|(1),
\&\fBnbdkit\-fua\-filter\fR\|(1),
\&\fBnbdkit\-noextents\-filter\fR\|(1).
.SH "AUTHORS"
.IX Header "AUTHORS"
Eric Blake
.PP
Nir Soffer
.PP
Richard W.M. Jones
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (C) 2013\-2020 Red Hat Inc.
.SH "LICENSE"
.IX Header "LICENSE"
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:
.IP "\(bu" 4
Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
.IP "\(bu" 4
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.
.IP "\(bu" 4
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.
.PP
\&\s-1THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS\s0 ''\s-1AS IS\s0'' \s-1AND
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\s0 (\s-1INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES\s0; \s-1LOSS OF
USE, DATA, OR PROFITS\s0; \s-1OR BUSINESS INTERRUPTION\s0) \s-1HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT\s0 (\s-1INCLUDING NEGLIGENCE OR OTHERWISE\s0) \s-1ARISING IN ANY WAY OUT
OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.\s0