jammy (1) nbdkit-blocksize-filter.1.gz

Provided by: nbdkit_1.24.1-2ubuntu4_amd64 bug

NAME

       nbdkit-blocksize-filter - nbdkit blocksize filter

SYNOPSIS

        nbdkit --filter=blocksize plugin [minblock=SIZE] [maxdata=SIZE] \
            [maxlen=SIZE] [plugin-args...]

DESCRIPTION

       "nbdkit-blocksize-filter" is a filter that ensures various block size limits are met on transactions
       presented to the plugin.  The NBD protocol permits clients to send requests with a granularity as small
       as 1 byte or as large as nearly 4 gigabytes, although it suggests that portable clients should align
       requests to 512 bytes and not exceed 32 megabytes without prior coordination with the server.

       Meanwhile, some plugins require requests to be aligned to 512-byte multiples, or may enforce a maximum
       transaction size to bound the time or memory resources spent by any one command (note that nbdkit itself
       refuses a read or write larger than 64 megabytes, while many other NBD servers limit things to 32
       megabytes).  The blocksize filter can be used to modify the client requests to meet the plugin
       restrictions.

PARAMETERS

       The nbdkit-blocksize-filter accepts the following parameters.

       minblock=SIZE
           The minimum block size and alignment to pass to the plugin.  This must be a power of two, and no
           larger than 64k.  If omitted, this defaults to 1 (that is, no minimum size restrictions).  The filter
           rounds up read requests to alignment boundaries, performs read-modify-write cycles for any unaligned
           head or tail of a write or zero request, and silently ignores any unaligned head or tail of a trim
           request.  The filter also truncates the plugin size down to an aligned value (as it cannot safely
           operate on the unaligned tail).  If you need to round the image size up instead to access the last
           few bytes, combine this filter with nbdkit-truncate-filter(1).

           This parameter understands the suffix 'k' for 1024.

       maxdata=SIZE
           The maximum block size for any single transaction with data (read and write).  If omitted, this
           defaults to 64 megabytes (that is, the nbdkit maximum).  This need not be a power of two, but must be
           an integer multiple of "minblock".  The filter fragments any larger client request into multiple
           plugin requests.

           This parameter understands the suffixes 'k', 'M', and 'G' for powers of 1024.

       maxlen=SIZE
           The maximum length for any single transaction without data (trim, zero or extents).  If omitted, this
           defaults to 0xffffffff rounded down to "minsize" alignment (that is, the inherent 32-bit limit of the
           NBD protocol).  This need not be a power of two, but must be an integer multiple of "minblock", and
           should be at least as large as "maxdata".  The filter fragments any larger client request into
           multiple plugin requests.

           This parameter understands the suffixes 'k', 'M', and 'G' for powers of 1024.

EXAMPLES

       Allow an arbitrary client to use the VDDK plugin (which is limited to 512-byte blocks), without having to
       fix the client to avoid sending unaligned requests:

        nbdkit --filter=blocksize vddk minblock=512 file=/absolute/path/to/file.vmdk

       Allow an arbitrary client tuned to nbdkit's 64 megabyte sizing to connect to a remote server that insists
       on 32 megabyte sizing, via the nbd plugin:

        nbdkit --filter=blocksize nbd maxdata=32M socket=/path/to/socket

       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-blocksize-filter.so
           The filter.

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

VERSION

       "nbdkit-blocksize-filter" first appeared in nbdkit 1.4.

SEE ALSO

       nbdkit(1), nbdkit-nbd-plugin(1), nbdkit-vddk-plugin(1), nbdkit-filter(3), nbdkit-truncate-filter(1).

AUTHORS

       Eric Blake

       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:

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

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           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.

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