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nbdkit-truncate-filter(1)	    NBDKIT	     nbdkit-truncate-filter(1)

NAME
       nbdkit-truncate-filter -	change the size	of plugins

SYNOPSIS
	nbdkit --filter=truncate plugin	[truncate=SIZE]
					[round-up=N] [round-down=N]

DESCRIPTION
       "nbdkit-truncate-filter"	is a filter that changes the size of the
       underlying plugin.  It can:

       o   Make	the plugin smaller (truncate it).  Use the "truncate=SIZE"
	   parameter to	set the	smaller	size.

       o   Make	the plugin larger (the additional bytes	read back as zeroes).
	   Use "truncate=SIZE" to set the larger size.

       o   Round the size of the plugin	up or down to the next multiple	of
	   "N".	 Use either "round-up=N" or "round-down=N".

       A common	use for	this filter is to handle NBD clients which have	a
       problem dealing with device sizes which are not a multiple of 512
       bytes.  Use "round-up=512" to round the size up to the next multiple of
       512 bytes.  If the size is already a multiple of	512 bytes then this
       has no effect.

PARAMETERS
       truncate=SIZE
	   Set the absolute size in bytes of the apparent device.  This	may be
	   smaller or larger or	the same as the	underlying plugin.

	   If the size is larger than the underlying plugin, reading the extra
	   space returns zeroes.  Writes are also permitted to the extra
	   space, but you must only write zeroes (any attempts to write	non-
	   zero	bytes will return an error back	to the client).

	   This	parameter is optional.

       round-up=N
	   Round the size up to	the next multiple of "N" bytes.	 If the	size
	   of the underlying plugin is already a multiple of "N" bytes,	this
	   has no effect.

	   This	option is useful when combined with other filters (such	as
	   nbdkit-blocksize-filter(1), nbdkit-cache-filter(1), or
	   nbdkit-cow-filter(1)) that normally round down due to a larger
	   granularity,	in order to access the last few	bytes of a file	that
	   would otherwise be rendered inaccessible.

	   This	parameter is optional.

       round-down=N
	   Round the size down to a multiple of	"N" bytes.  If the size	of the
	   underlying plugin is	already	a multiple of "N" bytes, this has no
	   effect.

	   This	parameter is optional.

EXAMPLES
       Serve a file as if it were a block device that insists on 4k alignment,
       while still allowing access to any unaligned bytes at the end of	the
       file:

	nbdkit --filter=blocksize --filter=truncate file /path/to/file \
	minblock=4k round-up=4k

FILES
       $filterdir/nbdkit-truncate-filter.so
	   The filter.

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

VERSION
       "nbdkit-truncate-filter"	first appeared in nbdkit 1.6.

SEE ALSO
       nbdkit(1), nbdkit-file-plugin(1), nbdkit-filter(3),
       nbdkit-blocksize-filter(1), nbdkit-cache-filter(1),
       nbdkit-cow-filter(1), nbdkit-offset-filter(1),
       nbdkit-partition-filter(1).

AUTHORS
       Richard W.M. Jones

COPYRIGHT
       Copyright (C) 2018 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:

       o   Redistributions of source code must retain the above	copyright
	   notice, this	list of	conditions and the following disclaimer.

       o   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.

       o   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-1.20.4			  2021-09-21	     nbdkit-truncate-filter(1)

NAME | SYNOPSIS | DESCRIPTION | PARAMETERS | EXAMPLES | FILES | VERSION | SEE ALSO | AUTHORS | COPYRIGHT | LICENSE

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