ultrix man page for nbuf

nbuf(4) 						     Kernel Interfaces Manual							   nbuf(4)

Name
       nbuf - select multiple-buffer operation to a raw device

Syntax
       #include <sys/ioctl.h>

       ioctl(d, FIONBUF, count)
       int d;
       int *count;

       status=ioctl(d, FIONBDONE, buffer)
       int d, status;
       char **buffer;

Description
       The I/O operations to raw devices are usually performed through a single buffer. This means that the issuing process must wait for a buffer
       to complete before the process can do anything else. An N-buffered I/O operation allows a process to begin an I/O  operation  and  continue
       doing  something else until the operation has finished. Once N-buffered operation is enabled, and acts as before except that buffer comple-
       tion is not guaranteed when the call returns.  If the operation starts without errors, and return as  if  the  operation  were  successful.
       That  is,  the  number of requested bytes have transferred and file pointers are updated.  On read operations, the process must not use the
       contents of the started buffer until the buffer actually completes.  On write operations, the process must not reuse the buffer	until  the
       operation  actually  completes.	A second is used to check the status of previously issued N-buffered read/write requests to determine when
       the operation has really completed.

       N-buffered I/O is used through a set of calls.  Setting the request argument in an call to FIONBUF enables count buffers to  be	used  with
       the raw device associated with the file descriptor d.  If count is zero, the N-buffered operation is terminated and any pending buffers are
       completed. A count less than zero is invalid.  Any started I/O buffer's status is checked by the call with  the	request  argument  set	to
       FIONBDONE,  with  the  address  of the buffer used as an argument.  The status field returns the actual byte count transferred or any error
       encountered on the I/O operation. The FIONBDONE ioctl must be called before re-using a buffer. FIONBDONE blocks the process until the given
       buffer  completes  (unless FNDELAY has been specified with at which point EWOULDBLOCK is returned).  In addition, a signal can be generated
       whenever a buffer completes, if FIOASYNC has been specified with

       The call is also useful in checking on the status of pending buffers.  The call returns immediately if less than count operations have been
       started on an N-buffered channel. Otherwise, blocks the specified amount of time for a buffer to become done. At this point, FIONBDONE must
       be used to return actual status of the pending buffer.

Diagnostics
       The call fails if one or more of the following are true:

       [EBADF]	      The d argument is not a valid descriptor.

       [ENOTTY]       The d argument is not associated with a character special device.

       [ENOTTY]       The specified request does not apply to the kind of object which the descriptor d references.

       [EINVAL]       The request or argp argument is not valid. Returned for FIONBDONE, if requested buffer was never started. Also returned  for
		      FIONBUF, if this device does not support N-buffered I/O.

See Also
       fcntl(2), ioctl(2), select(2)

																	   nbuf(4)