sys_uio.h

<sys/uio.h>(P)						       <sys/uio.h>(P)



NAME
       sys/uio.h - definitions for vector I/O operations

SYNOPSIS
       #include <sys/uio.h>

DESCRIPTION
       The  <sys/uio.h> header shall define the iovec structure that includes
       at least the following members:


	      void   *iov_base	Base address of a memory region for input or output.
	      size_t  iov_len	The size of the memory pointed to by iov_base.

       The <sys/uio.h> header uses the	iovec  structure  for  scatter/gather
       I/O.

       The  ssize_t  and  size_t  types	 shall	be  defined  as	 described in
       <sys/types.h>.

       The following shall be declared as functions and may also  be  defined
       as macros. Function prototypes shall be provided.


	      ssize_t readv(int, const struct iovec *, int);
	      ssize_t writev(int, const struct iovec *, int);

       The following sections are informative.

APPLICATION USAGE
       The  implementation  can	 put  a limit on the number of scatter/gather
       elements which can be processed in  one	call.  The  symbol  {IOV_MAX}
       defined	in <limits.h> should always be used to learn about the limits
       instead of assuming a fixed value.

RATIONALE
       Traditionally, the maximum number of scatter/gather elements the	 sys-
       tem  can	 process  in  one  call	 were described by the symbolic value
       {UIO_MAXIOV}. In IEEE Std 1003.1-2001 this value is  replaced  by  the
       constant {IOV_MAX} which can be found in <limits.h>.

FUTURE DIRECTIONS
       None.

SEE ALSO
       <limits.h>   ,	<sys/types.h>  ,  the  System  Interfaces  volume  of
       IEEE Std 1003.1-2001, read(), write()

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic	 form
       from  IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface  (POSIX),  The  Open	Group
       Base  Specifications Issue 6, Copyright (C) 2001-2003 by the Institute
       of Electrical and Electronics Engineers, Inc and The  Open  Group.  In
       the  event  of  any  discrepancy between this version and the original
       IEEE and The Open Group Standard, the original IEEE and The Open Group
       Standard	 is  the  referee  document.  The  original  Standard  can be
       obtained online at http://www.opengroup.org/unix/online.html .



POSIX				     2003		       <sys/uio.h>(P)