Useful nbdkit filters: the error filter

nbdkit --filter=error [...] error=EIO error-rate=10%

nbdkit --filter=error [...] error-rate=100% error-file=/tmp/inject

Errors can be injected randomly with a uniform distribution.
More usefully you can trigger errors from the presence of an error file.
NBD protocol only supports: EPERM, EIO, ENOMEM, EINVAL, ENOSPC or ESHUTDOWN.

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