NAME

       nbdkit-log-filter - nbdkit log filter

SYNOPSIS

        nbdkit --filter=log plugin logfile=FILE [logappend=BOOL] [plugin-args...]

DESCRIPTION

       "nbdkit-log-filter" is a filter that logs all transactions.  When used as the first
       filter, it can show the original client requests; as a later filter, it can show how
       earlier filters have modified the original request.  The log results are placed in a user-
       specified file; for more details on the log format, see FILES.  Note that using "nbdkit -v
       -f" produces much more verbose logging details to stderr about every aspect of nbdkit
       operation, although this requires running nbdkit in the foreground; while the log filter
       is designed to work even when nbdkit is run as a daemon.

PARAMETERS

       The nbdkit-log-filter requires a single parameter "logfile" which specifies the path of
       the file to use for logging.  If the file already exists, it will be truncated unless the
       "logappend" parameter was specified with a value that can be parsed as a boolean true.

EXAMPLES

       Serve the file disk.img, and log each client transaction in the file disk.log:

        nbdkit --filter=log file disk.img logfile=disk.log

       Repeat the task, but with the cow (copy-on-write) filter to perform local caching of data
       served from the original plugin:

        nbdkit --filter=cow --filter=log file disk.img logfile=disk.log2

       After running a client that performs the same operations under each of the two servers,
       you can compare disk.log and disk.log2 to see the impact of the caching.

FILES

       "logfile=FILE" parameter
           This filter writes to the file specified by the "logfile=FILE" parameter.  All lines
           include a timestamp, a connection counter, then details about the command.  The
           following actions are logged: Connect, Read, Write, Zero, Trim, Extents, Cache, Flush,
           and Disconnect.  Except for Connect and Disconnect, an event is logged across two
           lines for call and return value, to allow tracking duration and tracing any parallel
           execution, using id for correlation (incremented per action on the connection).

           An example logging session of a client that performs a single successful read is:

            2018-01-27 20:38:22.959984 connection=1 Connect size=0x400 write=1 flush=1 rotational=0 trim=0 zero=1 fua=1 extents=1 cache=0 fast_zero=0
            2018-01-27 20:38:23.001720 connection=1 Read id=1 offset=0x0 count=0x100 ...
            2018-01-27 20:38:23.001995 connection=1 ...Read id=1 return=0 (Success)
            2018-01-27 20:38:23.044259 connection=1 Disconnect transactions=1

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

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

VERSION

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

SEE ALSO

       nbdkit(1), nbdkit-file-plugin(1), nbdkit-cow-filter(1), nbdkit-filter(3),
       nbdkit-stats-filter(1).

AUTHORS

       Eric Blake

COPYRIGHT

       Copyright (C) 2018 Red Hat Inc.

LICENSE

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