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.\" ========================================================================
.\"
.IX Title "nbdkit-offset-filter 1"
.TH nbdkit-offset-filter 1 "2019-01-26" "nbdkit-1.10.3" "NBDKIT"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
nbdkit\-offset\-filter \- nbdkit offset filter
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& nbdkit \-\-filter=offset plugin offset=OFFSET range=LENGTH [plugin\-args...]
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\f(CW\*(C`nbdkit\-offset\-filter\*(C'\fR is a filter that limits requests to the byte
range \f(CW\*(C`[offset .. offset+range\-1]\*(C'\fR within another plugin.
.SH "PARAMETERS"
.IX Header "PARAMETERS"
.IP "\fBoffset=\fR\s-1OFFSET\s0" 4
.IX Item "offset=OFFSET"
The start offset.  The offset must be ≥ 0.
.Sp
This parameter is optional.  If not given then \f(CW\*(C`offset=0\*(C'\fR is assumed.
.IP "\fBrange=\fR\s-1LENGTH\s0" 4
.IX Item "range=LENGTH"
The length of data to serve.
.Sp
This parameter is optional.  If not given then the range is served
starting from the offset through to the end of the underlying
file/device.
.PP
Note it is an error if the offset and/or range specify data which lies
beyond the end of the underlying device.  Use
\&\fBnbdkit\-truncate\-filter\fR\|(1) to truncate or extend the size of
plugins.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
.SS "Serve part of a file"
.IX Subsection "Serve part of a file"
Using \fBnbdkit\-file\-plugin\fR\|(1), serve the file \f(CW\*(C`disk.img\*(C'\fR starting at
offset \f(CW\*(C`1M\*(C'\fR.  The total length served is \f(CW\*(C`100M\*(C'\fR (the underlying file
must therefore be at least \f(CW\*(C`101M\*(C'\fR in length):
.PP
.Vb 1
\& nbdkit \-\-filter=offset file disk.img offset=1M range=100M
.Ve
.SS "Serve a single partition"
.IX Subsection "Serve a single partition"
\&\fIAn easier way to do this is with \f(BInbdkit\-partition\-filter\fI\|(1).\fR
.PP
One way to serve a single partition from a disk is to find the start
and length of the partition, eg using:
.PP
.Vb 4
\& $ parted disk.img \-\- unit b print
\& ...
\& Number  Start   End         Size        Type     File system  Flags
\&  1      65536B  104792575B  104727040B  primary  ext2
.Ve
.PP
You can then serve the partition only using:
.PP
.Vb 1
\& nbdkit \-\-filter=offset file disk.img offset=65536 range=104727040
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBnbdkit\fR\|(1),
\&\fBnbdkit\-file\-plugin\fR\|(1),
\&\fBnbdkit\-filter\fR\|(3),
\&\fBnbdkit\-partition\-filter\fR\|(1),
\&\fBnbdkit\-truncate\-filter\fR\|(1).
.SH "AUTHORS"
.IX Header "AUTHORS"
Eric Blake
.PP
Richard W.M. Jones
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (C) 2018 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