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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 .