nbdkit-delay-filter - Man Page

 nbdkit --filter=delay plugin [plugin-args ...]
          delay-read=DELAY
          delay-write=DELAY
          delay-zero=DELAY
          delay-trim=DELAY
          delay-extents=DELAY
          delay-cache=DELAY
          delay-open=DELAY
          delay-close=DELAY
          delay-fast-zero=BOOL

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

nbdkit-delay-filter is a filter for nbdkit(1) that delays read and write requests.  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.  To simulate a spinning disk see nbdkit-spinning-filter(1).

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

In nbdkit ≥ 1.40, nbdkit_parse_delay(3) is used to parse the delay parameters, so a wide variety of formats are accepted, such as:

delay-read=1.5

delay-write=100ms

delay-zero=1.2μs

delay-trim=1000ns

In nbdkit ≤ 1.38, only a whole number of seconds, or a whole number of milliseconds (if suffixed by ms) were allowed.

rdelay=DELAY

delay-read=DELAY

Delay read operations by DELAY.

The two forms rdelay and delay-read work identically.

delay-write=DELAY

Delay write operations by DELAY.

delay-zero=DELAY

(nbdkit ≥ 1.10)

Delay zero operations by DELAY.  See also delay-fast-zero.

delay-trim=DELAY

(nbdkit ≥ 1.10)

Delay trim/discard operations by DELAY.

delay-extents=DELAY

(nbdkit ≥ 1.12)

Delay block status (extents) operations by DELAY.

delay-cache=DELAY

(nbdkit ≥ 1.14)

Delay advisory cache operations by DELAY.

wdelay=DELAY

Delay write, zero and trim operations by DELAY.

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=DELAY

(nbdkit ≥ 1.28)

Delay open (client connection) by DELAY.

delay-close=DELAY

(nbdkit ≥ 1.28)

Delay close (client disconnection) by DELAY.  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.

$filterdir/nbdkit-delay-filter.so

The filter.

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

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

nbdkit(1), nbdkit-filter(3), nbdkit-pause-filter(1), nbdkit-rate-filter(1), nbdkit-spinning-filter(1), nbdkit_parse_delay(3).

Richard W.M. Jones

Copyright Red Hat

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(1), nbdkit-evil-filter(1), nbdkit-file-plugin(1), nbdkit-filter(3), nbdkit_nanosleep(3), nbdkit_parse_delay(3), nbdkit-pause-filter(1), nbdkit-rate-filter(1), nbdkit-release-notes-1.10(1), nbdkit-release-notes-1.14(1), nbdkit-release-notes-1.28(1), nbdkit-release-notes-1.40(1), nbdkit-spinning-filter(1).