nbdkit-delay-filter(1)

NAME
nbdkit-delay-filter - nbdkit delay filter

SYNOPSIS
 nbdkit --filter=delay plugin rdelay=SECS wdelay=SECS [plugin-args...]

 nbdkit --filter=delay plugin rdelay=NNms wdelay=NNms [plugin-args...]

 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)

DESCRIPTION
"nbdkit-delay-filter" 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 nbdkit-rate-filter(1) instead.

EXAMPLES
Delays reads and writes by 100ms:

 nbdkit --filter=delay file disk.img rdelay=100ms wdelay=100ms

Delay only zero operations by 1 second, nothing else is affected:

 nbdkit --filter=delay file disk.img delay-zero=1

PARAMETERS

rdelay=SECS
rdelay=NNms
delay-read=SECS
delay-read=NNms
    Delay read operations by "SECS" seconds or "NN" milliseconds.

    The two forms "rdelay" and "delay-read" work identically.

delay-write=SECS
delay-write=NNms
    Delay write operations by "SECS" seconds or "NN" milliseconds.

delay-zero=SECS
delay-zero=NNms
    (nbdkit ≥ 1.10)

    Delay zero operations by "SECS" seconds or "NN" milliseconds. See also delay-fast-zero.

delay-trim=SECS
delay-trim=NNms
    (nbdkit ≥ 1.10)

    Delay trim/discard operations by "SECS" seconds or "NN" milliseconds.

delay-extents=SECS
delay-extents=NNms
    (nbdkit ≥ 1.12)

    Delay block status (extents) operations by "SECS" seconds or "NN" milliseconds.

delay-cache=SECS
delay-cache=NNms
    (nbdkit ≥ 1.14)

    Delay advisory cache operations by "SECS" seconds or "NN" milliseconds.

wdelay=SECS
wdelay=NNms
    Delay write, zero and trim operations by "SECS" seconds or "NN" milliseconds.

delay-fast-zero=BOOL
    (nbdkit ≥ 1.16)

    The NBD specification documents an extension called fast zero, in which the client may request that a server should reply with "ENOTSUP" 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.

delay-open=SECS
delay-open=NNms
    (nbdkit ≥ 1.28)

    Delay open (client connection) by "SECS" seconds or "NN" milliseconds.

delay-close=SECS
delay-close=NNms
    (nbdkit ≥ 1.28)

    Delay close (client disconnection) by "SECS" seconds or "NN" 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 "NBD_CMD_DISC" / libnbd function nbd_shutdown(3)). Clients that abruptly disconnect from the server cannot be delayed.

FILES

$filterdir/nbdkit-delay-filter.so
    The filter.

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

VERSION
"nbdkit-delay-filter" first appeared in nbdkit 1.2, based on earlier "rdelay" and "wdelay" options in nbdkit-file-plugin(1).

SEE ALSO
nbdkit(1), nbdkit-filter(3), nbdkit-pause-filter(1), nbdkit-rate-filter(1).

AUTHORS
Richard W.M. Jones

COPYRIGHT
Copyright (C) 2018-2021 Red Hat Inc.

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.