nbdkit-delay-filter(1)

NAME
nbdkit-delay-filter - nbdkit delay filter

SYNOPSIS
 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
          delay-trigger=FILENAME

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

DESCRIPTION
"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).

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

DELAY FORMAT
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.

TRIGGERED DELAYS
Using the "delay-trigger=FILENAME" option, you can disable this filter until the named FILENAME is created. If the file is deleted, then the filter is disabled again. This allows you to boot up a virtual machine before turning on delays.

PARAMETERS

delay-cache=DELAY
    (nbdkit ≥ 1.14)

    Delay advisory cache operations 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.

delay-extents=DELAY
    (nbdkit ≥ 1.12)

    Delay block status (extents) 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-read=DELAY
rdelay=DELAY
    Delay read operations by "DELAY".

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

delay-trigger=FILENAME
    (nbdkit ≥ 1.46)

    If this option is used, the filter is only enabled when the file called FILENAME exists. Therefore this file may be created and deleted while nbdkit is running to enable and disable delays.

delay-trim=DELAY
    (nbdkit ≥ 1.10)

    Delay trim/discard operations by "DELAY".

delay-write=DELAY
    Delay write operations by "DELAY".

delay-zero=DELAY
    (nbdkit ≥ 1.10)

    Delay zero operations by "DELAY". See also the "delay-fast-zero" option.

wdelay=DELAY
    Delay write, zero and trim operations by "DELAY". (This is the same as setting "delay-write", "delay-zero" and "delay-trim" options together.)

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

AUTHORS
Richard W.M. Jones

COPYRIGHT
Copyright Red Hat

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.