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.\" ========================================================================
.\"
.IX Title "nbdkit-delay-filter 1"
.TH nbdkit-delay-filter 1 2024-04-21 nbdkit-1.38.1 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\-delay\-filter \- nbdkit delay filter
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& nbdkit \-\-filter=delay plugin rdelay=SECS wdelay=SECS [plugin\-args...]
.Ve
.PP
.Vb 1
\& nbdkit \-\-filter=delay plugin rdelay=NNms wdelay=NNms [plugin\-args...]
.Ve
.PP
.Vb 10
\& nbdkit \-\-filter=delay plugin [plugin\-args ...]
\&          delay\-read=(SECS|NNms)
\&          delay\-write=(SECS|NNms)
\&          delay\-zero=(SECS|NNms)
\&          delay\-trim=(SECS|NNms)
\&          delay\-extents=(SECS|NNms)
\&          delay\-cache=(SECS|NNms)
\&          delay\-fast\-zero=BOOL
\&          delay\-open=(SECS|NNms)
\&          delay\-close=(SECS|NNms)
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
\&\f(CW\*(C`nbdkit\-delay\-filter\*(C'\fR is a filter that delays read and write requests
by some seconds or milliseconds.  This is used to simulate a slow or
remote server, or to test certain kinds of race conditions in Linux.
To limit server bandwidth use \fBnbdkit\-rate\-filter\fR\|(1) instead.
.SH EXAMPLES
.IX Header "EXAMPLES"
Delays reads and writes by 100ms:
.PP
.Vb 1
\& nbdkit \-\-filter=delay file disk.img rdelay=100ms wdelay=100ms
.Ve
.PP
Delay only zero operations by 1 second, nothing else is affected:
.PP
.Vb 1
\& nbdkit \-\-filter=delay file disk.img delay\-zero=1
.Ve
.SH PARAMETERS
.IX Header "PARAMETERS"
.IP \fBrdelay=\fRSECS 4
.IX Item "rdelay=SECS"
.PD 0
.IP \fBrdelay=\fRNN\fBms\fR 4
.IX Item "rdelay=NNms"
.IP \fBdelay\-read=\fRSECS 4
.IX Item "delay-read=SECS"
.IP \fBdelay\-read=\fRNN\fBms\fR 4
.IX Item "delay-read=NNms"
.PD
Delay read operations by \f(CW\*(C`SECS\*(C'\fR seconds or \f(CW\*(C`NN\*(C'\fR milliseconds.
.Sp
The two forms \f(CW\*(C`rdelay\*(C'\fR and \f(CW\*(C`delay\-read\*(C'\fR work identically.
.IP \fBdelay\-write=\fRSECS 4
.IX Item "delay-write=SECS"
.PD 0
.IP \fBdelay\-write=\fRNN\fBms\fR 4
.IX Item "delay-write=NNms"
.PD
Delay write operations by \f(CW\*(C`SECS\*(C'\fR seconds or \f(CW\*(C`NN\*(C'\fR milliseconds.
.IP \fBdelay\-zero=\fRSECS 4
.IX Item "delay-zero=SECS"
.PD 0
.IP \fBdelay\-zero=\fRNN\fBms\fR 4
.IX Item "delay-zero=NNms"
.PD
(nbdkit ≥ 1.10)
.Sp
Delay zero operations by \f(CW\*(C`SECS\*(C'\fR seconds or \f(CW\*(C`NN\*(C'\fR milliseconds.  See
also \fBdelay-fast-zero\fR.
.IP \fBdelay\-trim=\fRSECS 4
.IX Item "delay-trim=SECS"
.PD 0
.IP \fBdelay\-trim=\fRNN\fBms\fR 4
.IX Item "delay-trim=NNms"
.PD
(nbdkit ≥ 1.10)
.Sp
Delay trim/discard operations by \f(CW\*(C`SECS\*(C'\fR seconds or \f(CW\*(C`NN\*(C'\fR milliseconds.
.IP \fBdelay\-extents=\fRSECS 4
.IX Item "delay-extents=SECS"
.PD 0
.IP \fBdelay\-extents=\fRNN\fBms\fR 4
.IX Item "delay-extents=NNms"
.PD
(nbdkit ≥ 1.12)
.Sp
Delay block status (extents) operations by \f(CW\*(C`SECS\*(C'\fR seconds or \f(CW\*(C`NN\*(C'\fR
milliseconds.
.IP \fBdelay\-cache=\fRSECS 4
.IX Item "delay-cache=SECS"
.PD 0
.IP \fBdelay\-cache=\fRNN\fBms\fR 4
.IX Item "delay-cache=NNms"
.PD
(nbdkit ≥ 1.14)
.Sp
Delay advisory cache operations by \f(CW\*(C`SECS\*(C'\fR seconds or \f(CW\*(C`NN\*(C'\fR
milliseconds.
.IP \fBwdelay=\fRSECS 4
.IX Item "wdelay=SECS"
.PD 0
.IP \fBwdelay=\fRNN\fBms\fR 4
.IX Item "wdelay=NNms"
.PD
Delay write, zero and trim operations by \f(CW\*(C`SECS\*(C'\fR seconds or \f(CW\*(C`NN\*(C'\fR
milliseconds.
.IP \fBdelay\-fast\-zero=\fRBOOL 4
.IX Item "delay-fast-zero=BOOL"
(nbdkit ≥ 1.16)
.Sp
The NBD specification documents an extension called fast zero, in
which the client may request that a server should reply with
\&\f(CW\*(C`ENOTSUP\*(C'\fR as soon as possible if the zero operation offers no real
speedup over a corresponding write.  By default, this parameter is
true, and fast zero requests are serviced by the plugin after the same
delay as any other zero request; but setting this parameter to false
instantly fails a fast zero response without waiting for or consulting
the plugin.
.IP \fBdelay\-open=\fRSECS 4
.IX Item "delay-open=SECS"
.PD 0
.IP \fBdelay\-open=\fRNN\fBms\fR 4
.IX Item "delay-open=NNms"
.PD
(nbdkit ≥ 1.28)
.Sp
Delay open (client connection) by \f(CW\*(C`SECS\*(C'\fR seconds or \f(CW\*(C`NN\*(C'\fR
milliseconds.
.IP \fBdelay\-close=\fRSECS 4
.IX Item "delay-close=SECS"
.PD 0
.IP \fBdelay\-close=\fRNN\fBms\fR 4
.IX Item "delay-close=NNms"
.PD
(nbdkit ≥ 1.28)
.Sp
Delay close (client disconnection) by \f(CW\*(C`SECS\*(C'\fR seconds or \f(CW\*(C`NN\*(C'\fR
milliseconds.  This can also cause server shutdown to be delayed if
clients are connected at the time.  This only affects clients that
gracefully disconnect (using \f(CW\*(C`NBD_CMD_DISC\*(C'\fR / libnbd function
\&\fBnbd_shutdown\fR\|(3)).  Clients that abruptly disconnect from the server
cannot be delayed.
.SH FILES
.IX Header "FILES"
.ie n .IP \fR\fI$filterdir\fR\fI/nbdkit\-delay\-filter.so\fR 4
.el .IP \fR\f(CI$filterdir\fR\fI/nbdkit\-delay\-filter.so\fR 4
.IX Item "$filterdir/nbdkit-delay-filter.so"
The filter.
.Sp
Use \f(CW\*(C`nbdkit \-\-dump\-config\*(C'\fR to find the location of \f(CW$filterdir\fR.
.SH VERSION
.IX Header "VERSION"
\&\f(CW\*(C`nbdkit\-delay\-filter\*(C'\fR first appeared in nbdkit 1.2, based on earlier
\&\f(CW\*(C`rdelay\*(C'\fR and \f(CW\*(C`wdelay\*(C'\fR options in \fBnbdkit\-file\-plugin\fR\|(1).
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBnbdkit\fR\|(1),
\&\fBnbdkit\-filter\fR\|(3),
\&\fBnbdkit\-pause\-filter\fR\|(1),
\&\fBnbdkit\-rate\-filter\fR\|(1).
.SH AUTHORS
.IX Header "AUTHORS"
Richard W.M. Jones
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright Red Hat
.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
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.