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     cstream - direct data streams, with bandwidth limiting, FIFO, audio,
     duplication and extended reporting support.


     cstream [-b num] [-B num] [-i filename] [-I string] [-l] [-n num]
             [-o filename] [-O string] [-p filename] [-t num] [-T num]
             [-v num] [-V] [filename]


     Cstream filters data streams, much like the UNIX tool dd(1).  It has a
     more traditional command line syntax, support for precise bandwidth
     limiting and reporting and support for FIFOs. Data limits and throughput
     rate calculation will work for files > 4 GB.

     Cstream reads from the standard input and writes to the standard output,
     if no filenames are given. It will also ’generate’ or ’sink’ data if


     -b num    Set the block size used for read/write to num.  The default is
               8192 bytes.

     -B num    Buffer input up to num bytes before writing. The default is the
               blocksize. It is an error to set this to anything below the
               blocksize. Useful when writing tapes and similar that prefer
               few large writes of many small.

     -c num    Concurrent operation. Use a separate process for output. This
               is especially useful in combination with the -B option.
               0 = use one process only (default)
               1 = read process will buffer
               2 = write process will buffer
               3 = both processes will buffer.
                   In combination with a large buffer size this will often
                   load your memory heavily, every time the reader transfers
                   the buffer it collected to the writer. If you use -c 3 and
                   have a buffer size of 128 Megabytes 256 MB of memory will
                   be touched at once.

     -i num

     -o num    Set the file names to use for input or output, respectively. If
               the output file name is "-", data will just be discarded. If
               the input file name is "-", data will be generated ’out of the
               void’. If these options aren’t given, stdin/stout will be used.
               If you need to give -o or -i options and want stdin/stdout,
               specify the empty string, like this:

               cstream -i’’

               If TCP support has been compiled in (default),
               hostname:portnumber will try to connect to the specified host
               at the specified port and :portnumber will open a TCP socket on
               the local machine and wait for a connection to arrive. SECURITY
               NOTE: cstream includes no mechanism to restrict the hosts that
               may connect to this port. Unless your machine has other network
               filters, anyone will be able to connect.

     -I string

     -O string
               Specify the type of input and output file, respectively.
               If string
                   includes ’f’, a fifo will be created.
               If string
                   includes ’a’, the file will be assumed to be an opensound-
                   compatible audio device and will be switched to CD-like
               If string
                   includes ’t’, a copy of the stream will be sent to file
                   descriptor 3.
               If string
                   includes ’N’, TCP will not be used for that file even if
                   the name has a ":".

     -l        Include line count in statistics.

     -n num    Limit the total amount of data to num.  If there is more input
               available, it will be discarded, cstream will exit after the
               limit has been reached. If there is less input, the limit will
               not be reached and no error will be signaled.

               num may have a trailing ’k’, ’m’ or ’g’ which means Kilobytes,
               Megabytes or Gigabytes (where Kilo = 1024). This applies to all
               numeric options.

     -p filename
               Write the process id of cstream to filename.  If cstream uses a
               separate writer process (option -c), this is the pid of the
               parent (reader) process.

     -t num    Limit the throughput of the data stream to num bytes/second.
               Limiting is done at the input side, you can rely on cstream not
               accepting more than this rate. If the number you give is
               positive, cstream accumulates errors and tries to keep the
               overall rate at the specified value, for the whole session. If
               you give a negative number, it is an upper limit for each
               read/write system call pair. In other words: the negative
               number will never exceed that limit, the positive number will
               exceed it to make good for previous underutilization.

     -T num    Report throughput every num seconds.

     -v num    Set verbose level to num.  By default, it is set to 0, which
               means no messages are displayed as long as no errors occur. A
               value of 1 means that total amount of data and throughput will
               be displayed at the end of program run. A value of 2 means the
               transfer rate since the end of the first read/write pair will
               also be reported (useful when there is an initial delay). A
               value of 3 means there will also be separate measurements for
               read and write. This option is resource-consuming and currently
               isn’t implemented. A value of 4 means that notices about each
               single read/write will be displayed. High values include all
               message types of lower values.

     -V        Print version number to stdout and exit with 0.

     filename  A single filename as the last argument without an option switch
               will be used as input file if -i has not been used.


     SIGINFO   Sending SIGUSR1 (or SIGINFO, which is usually mapped to
               Control-T on you keyboard) to cstream causes it to display
               throughput rates to stderr. The stream will continue as if
               nothing happened.

     SIGUSR2   Exit and report throughput rates, if requested.

     SIGHUP    I found myself sending SIGHUP accidentally too often. But
               ignoring or misusing SIGHUP is not an option for me. Thus, when
               cstream received SIGHUP, it will wait 5 seconds for another
               SIGHUP, to give users a chance to correct a possible mistake.
               If no additional SIGHUP is received, cstream kills itself with


     cstream -o tmpfile -v 1 -n 384m -i -
             Writes 384 Megabytes of unspecified data to file tmpfile and
             display verbose throughput rate. Makes a good benchmark, the
             speed of /dev/null varies too much from system to system.

     cstream -i tmpfile -v 1 -n 384m -o -
             Read the same file back in and discard data.

     cstream -b 2000  -t 10000 /var/log/messages
             Will display the file in a more or less watchable speed.

     dump 0sf 400000 - / | cstream -v 1 -b 32768 -o /dev/rst0 -p pidfile

     kill -USR1cat pidfile‘
             Write the output from dump(1) to tape. Each time the signal is
             sent, the throughput and data rate so far will be displayed.

     cstream -t 176400 -i /dev/dsp0 -I f -o -
             Makes kind of a soundcard emulator which may be used to test
             audio applications that need something to write to that limits
             the data rate as a real soundcard does. This obviously doesn’t
             work when the application tries to write data using mmap(2) and
             the application has to ignore errors when it tries to set
             soundcard parameters using ioctl(2).

     cstream -t 176400 -i /dev/dsp0 -I f -o /dev/dsp1 -O f
             Similar soundcard emulator, except that it allows you to grab the
             data your applications sends to it from the other fifo, while
             still having precise timing.

     cstream -Oa -o /dev/dsp0
             Connects port 3333 on host and whatever data
             it finds there will be sent to the soundcard, with appropriate
             settings for CD quality stero play.

     cstream -i myaudiofile.raw -o :17324
             This will open a TCP server on port 17324 and waits until someone
             connects (for example, the command line from the previous
             example). Then it will send the contents of myaudiofile.raw down
             the TCP stream (for the previous audio example, typically a CD
             audiotrack like you get from the tosha or cdparanoia utilities).

     cstream -OD -o myfile

             Write to file myfile with O_DIRECT.  That usually means that the
             filesystem buffer cache will not try to cache this file.  You can
             use that to prevent copying operations from eating up physical
             memory.  Note that when cstream encounters a write error it will
             switch the output file from O_DIRECT to a normal file and write
             all further blocks without O_DIRECT if writes without O_DIRECT
             succeed.  In practice that usually means that your last block, if
             not a multiple of the filesystem block size, will still be
             written into the file (the maximum amount of data written without
             O_DIRECT is your blocksize minus one).  That way cstream ensures
             that the output file has the length of the input, however odd the
             length was and no matter what restrictions your OS places on
             O_DIRECT output.  Again, cstream will *not* pad the output to the
             block size, you get the same file and file size as if not using
             O_DIRECT, at the cost of switching to non-O_DIRECT whenever a
             block is not the right size.

     cstream -i :3333 | dd obs=8192 | ./cstream -omyfile -v7 -OD
             This is what you need to do to buffer TCP input, so that the last
             cstream will not switch away from O_DIRECT prematurely because of
             short reads.  If your input can do short reads (e.g. from TCP),
             and you want to ensure that O_DIRECT stays in effect, you need a
             buffer between the TCP stream and the O_DIRECT stream.  Since
             cstream does not yet support different input and output block
             sizes, dd is suitable here.  Note that this is only necessary if
             the OS requires multiples of the filesystem block size for
             O_DIRECT.  At the time of this writing this construct is needed
             on Linux for using TCP streams with O_DIRECT, but it is not
             needed on FreeBSD.

     cstream -OS -o myfile
             Writes to file myfile with O_SYNC.  This means by the time the
             system call returns the data is known to be on disk.  This is not
             the same thing as O_DIRECT.  O_DIRECT can do its own buffering,
             with O_SYNC there is no buffering at all.  At the time of this
             writing, O_SYNC on both Linux and FreeBSD is very slow (1/5th to
             1/10th of normal write) and O_DIRECT is reasonably fast (1/4th to
             1/2 of normal write).  You can combined O_SYNC and O_DIRECT.


     Exit code 0 means success.

     Exit code 1 means a command line syntax usage error.

     Exit code 2 means other errors, especially system errors.


     There should be an option to begin writing directly after the first read
     ended and then fill the buffer with reads in the background.  Right now
     writing will not begin before the reader has filled the buffer completely
     for the first time.

     Not a bug: the code to do O_DIRECT is reasonably sophisticated.  It will
     fall back to normal I/O on errors.  But before doing that it knows about
     both filesystem blocksize requirements (will default I/O blocksize to
     whatever the filesystem of the output file is in) and page alignment
     requirements (I/O will happen from a page-aligned buffer).  However, the
     combination of concurrent read/writes (-c options) and O_DIRECT has not
     been tested beyond basic verification that it gets some tests right.


     dd(1), mkfifo(2)


     cstream was initially written by Martin Cracauer in 1998.  For updates
     and more information see