nbdkit-error-filter - Man Page

inject errors for testing clients

Synopsis

 nbdkit --filter=error PLUGIN
     [error=EPERM|EIO|ENOMEM|EINVAL|ENOSPC|ESHUTDOWN]
     [error-rate=10%|0.1]
     [error-file=/tmp/inject]
     [error-pread=...] [error-pread-rate=...] [error-pread-file=...]
     [error-pwrite=...] [error-pwrite-rate=...] [error-pwrite-file=...]
     [error-trim=...] [error-trim-rate=...] [error-trim-file=...]
     [error-zero=...] [error-zero-rate=...] [error-zero-file=...]
     [error-extents=...] [error-extents-rate=...] [error-extents-file=...]
     [error-cache=...] [error-cache-rate=...] [error-cache-file=...]

Description

nbdkit-error-filter is an nbdkit filter that injects random errors into replies from the server.  This is used for testing that NBD clients can handle errors.

All parameters are optional, but you should usually specify one of the error-rate or error-*-rate parameters, otherwise this filter will do nothing.

Examples

Inject a low rate of errors randomly into the connection:

 nbdkit --filter=error file disk.img error-rate=1%

Reading, trimming, cache and extents (block status) requests will be successful, but all writes and zeroing will return “No space left on device”:

 nbdkit --filter=error file disk.img \
                            error=ENOSPC \
                            error-pwrite-rate=100% \
                            error-zero-rate=100%

To make all connections fail hard 60 seconds after the server is started, use:

 rm -f /tmp/inject
 nbdkit --filter=error file disk.img \
                            error-rate=100% \
                            error-file=/tmp/inject
 sleep 60; touch /tmp/inject

Parameters

error=EPERM|EIO|ENOMEM|EINVAL|ENOSPC|ESHUTDOWN

When a random error is injected, you can select which one from the range of possible NBD errors (the NBD protocol only supports a limited range of error codes).

This parameter is optional and the default is EIO (“Input/output error”).

error-rate=N%
error-rate=0..1

The rate of injected errors per NBD request.  This can be expressed as either a percentage between 0% and 100% or as a probability between 0 and 1.  If 0% or 0 is used then no errors are ever injected, and if 100% or 1 is used then all requests return errors.

This parameter is optional and the default is 0%. Unless you set this, the filter will do nothing.

error-file=FILENAME

Errors will only be injected when FILENAME exists.  (Note you must also specify the error-rate).

You can use this for fine-grained control over when to inject errors, for example if you want to trigger an error at an exact moment during a test, arrange for this file to be created at the appropriate time. Or conversely to test error recovery in a client, create the file initially, and then delete it to check the client can recover.

This parameter is optional.

error-pread,  error-pread-rate,  error-pread-file.

Same as error, error-rate and error-file but only apply the settings to NBD pread requests.

error-pwrite,  error-pwrite-rate,  error-pwrite-file.

Same as error, error-rate and error-file but only apply the settings to NBD pwrite requests.

error-trim,  error-trim-rate,  error-trim-file.

Same as error, error-rate and error-file but only apply the settings to NBD trim requests.

error-zero,  error-zero-rate,  error-zero-file.

Same as error, error-rate and error-file but only apply the settings to NBD zero requests.

error-extents,  error-extents-rate,  error-extents-file.

(nbdkit ≥ 1.12)

Same as error, error-rate and error-file but only apply the settings to NBD block status requests to read extents.

error-cache,  error-cache-rate,  error-cache-file.

(nbdkit ≥ 1.14)

Same as error, error-rate and error-file but only apply the settings to NBD cache requests.

Notes

Peculiar debug output

If you are looking at the debugging output (using nbdkit -f -v) then you may see peculiar “errors” appearing when using this filter, for example:

 nbdkit: file.9: debug: error: pread count=1024 offset=0 flags=0x0

In fact these are not errors, nbdkit core is simply printing the name of the filter which happens to be "error".  When this filter injects an error you will see something like:

 nbdkit: file.4: error: injecting ENOSPC error into pwrite

Files

$filterdir/nbdkit-error-filter.so

The filter.

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

Version

nbdkit-error-filter first appeared in nbdkit 1.6.

See Also

nbdkit(1), nbdkit-file-plugin(1), nbdkit-full-plugin(1), nbdkit-filter(3).

Authors

Richard W.M. Jones

License

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

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.

Referenced By

nbdkit(1), nbdkit-filter(3), nbdkit-full-plugin(1), nbdkit-loop(1), nbdkit-release-notes-1.6(1).

2021-05-05 nbdkit-1.25.7