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

        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.

PARAMETERS

       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.

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.

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           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
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