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


       #include <sys/uio.h>


       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

       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.


       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.


       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>.




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


       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 .