NAME¶

nbdkit-noparallel-filter - nbdkit noparallel filter

SYNOPSIS¶

 nbdkit --filter=noparallel plugin [serialize=MODE] [plugin-args...]

DESCRIPTION¶

"nbdkit-noparallel-filter" is a filter that intentionally disables parallelism in handling requests from clients. It is mainly useful for evaluating timing differences between various levels of parallelism. It can also be used as a way to work around any bugs in a plugin's claimed level of parallel support, without recompiling the plugin, or to ease efforts when connecting with a client that can batch up several requests but is not prepared to handle out-of-order replies.

To limit the number of concurrent clients it's usually better to use nbdkit-limit-filter(1).

PARAMETERS¶

serialize=requests

serialize=all-requests

serialize=connections

Optional, controls how much serialization the filter will enforce. Mode requests (default) prevents a single client from having more than one in-flight request, but does not prevent parallel requests from a second connection (if the plugin supports that). Mode all-requests is stricter, enforcing that at most one request (regardless of connection) will be active, but does not prevent parallel connections (if the plugin supports that). Mode connections is strictest, where there can be at most one client at a time, and where the server will no longer advertise "NBD_FLAG_MULTI_CONN" to clients.

EXAMPLES¶

Serve the file disk.img, but disallow out-of-order transaction completion to a given client:

 nbdkit --filter=noparallel file disk.img

Serve the file disk.img, but allowing only one client at a time:

 nbdkit --filter=noparallel file serialize=connections disk.img

FILES¶

$filterdir/nbdkit-noparallel-filter.so

The filter.

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

VERSION¶

"nbdkit-noparallel-filter" first appeared in nbdkit 1.14.

SEE ALSO¶

nbdkit(1), nbdkit-file-plugin(1), nbdkit-filter(3), nbdkit-fua-filter(1), nbdkit-limit-filter(1), nbdkit-nocache-filter(1), nbdkit-noextents-filter(1), nbdkit-nozero-filter(1).

AUTHORS¶

Eric Blake

COPYRIGHT¶

Copyright (C) 2018-2020 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:

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