DOKK / manpages / debian 12 / nbdkit / nbdkit-offset-filter.1.en
nbdkit-offset-filter(1) NBDKIT nbdkit-offset-filter(1)

nbdkit-offset-filter - nbdkit offset filter

 nbdkit --filter=offset plugin offset=OFFSET range=LENGTH [plugin-args...]

"nbdkit-offset-filter" is a filter that limits requests to the byte range "[offset .. offset+range-1]" within another plugin.

The start offset. The offset must be ≥ 0.

This parameter is optional. If not given then "offset=0" is assumed.

The length of data to serve.

This parameter is optional. If not given then the range is served starting from the offset through to the end of the underlying file/device.

Note it is an error if the offset and/or range specify data which lies beyond the end of the underlying device. Use nbdkit-truncate-filter(1) to truncate or extend the size of plugins.

Using nbdkit-file-plugin(1), serve the file "disk.img" starting at offset "1M". The total length served is "100M" (the underlying file must therefore be at least "101M" in length):

 nbdkit --filter=offset file disk.img offset=1M range=100M

An easier way to do this is with nbdkit-partition-filter(1).

One way to serve a single partition from a disk is to find the start and length of the partition, eg using:

 $ parted disk.img -- unit b print
 ...
 Number  Start   End         Size        Type     File system  Flags
  1      65536B  104792575B  104727040B  primary  ext2

You can then serve the partition only using:

 nbdkit --filter=offset file disk.img offset=65536 range=104727040

$filterdir/nbdkit-offset-filter.so
The filter.

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

"nbdkit-offset-filter" first appeared in nbdkit 1.2.

nbdkit(1), nbdkit-file-plugin(1), nbdkit-filter(3), nbdkit-partition-filter(1), nbdkit-protect-filter(1), nbdkit-tar-filter(1), nbdkit-truncate-filter(1).

Eric Blake

Richard W.M. Jones

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2023-01-04 nbdkit-1.32.5