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nbdkit-extentlist-filter(1)	    NBDKIT	   nbdkit-extentlist-filter(1)

NAME
       nbdkit-extentlist-filter	- place	extent list over a plugin

SYNOPSIS
	nbdkit -r --filter=extentlist plugin extentlist=FILENAME

DESCRIPTION
       "nbdkit-extentlist-filter" is an	nbdkit filter that lets	you place a
       static list of extents on top of	an existing plugin.  Extents record
       whether or not specific parts of	the disk are allocated or sparse.

       You can use this	with plugins which cannot get extent information
       themselves, but where you can get this information from another source.
       One place where it is useful is with nbdkit-ssh-plugin(1) because the
       sftp protocol does not support reading sparseness information, but you
       may be able to get this information directly from the source disk on
       the remote server using commands	such as	xfs_bmap(8).  A	similar
       situation applies to nbdkit-curl-plugin(1).

       Note that the extent list is read-only.	This filter does not monitor
       writes and trims	in order to update the extent list.  What can happen
       is that you would write to a aholea in the disk,	but would not be able
       to read it back because the NBD client would still think	that part of
       the disk	is a hole.  So it is generally only safe to use	this filter in
       read-only mode (-r option).

FILE FORMAT
       The list	of extents is specified	in a text file.	 There is one extent
       specified per line.  Each line has the format:

	offset length type

       The "offset" and	"length" fields	may use	any format understood by
       "nbdkit_parse_size".  The optional "type" field may be an integer,
       missing (same as	0), or a comma-separated list of the words "hole" and
       "zero".	(The fields correspond to the inputs of	the
       "nbdkit_add_extent" function, see nbdkit-plugin(3)).

       An example of a valid set of extents covering a "10M" disk where	the
       first megabyte only is allocated	data:

	0  1M
	1M 9M  hole,zero

       Or you could omit the "hole,zero" extent	since any gaps are assumed to
       be holes	with that type:

	0  1M

       The extent list need not	cover the whole	disk, and does not need	to be
       in ascending order, but it must not contain overlapping extents.

PARAMETERS
       extentlist=FILENAME
	   Specify the file containing the extent list,	in the format
	   described in	"FILE FORMAT" above.

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

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

VERSION
       "nbdkit-extentlist-filter" first	appeared in nbdkit 1.18.

SEE ALSO
       nbdkit(1), nbdkit-cacheextents-filter(1), nbdkit-noextents-filter(1),
       nbdkit-filter(3), nbdkit-plugin(3).

AUTHORS
       Richard W.M. Jones

COPYRIGHT
       Copyright (C) 2020 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			  2021-11-05	   nbdkit-extentlist-filter(1)

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

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