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 system 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 Technology -- 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 .