sys_uio.h(0P)		   POSIX Programmer's Manual		 sys_uio.h(0P)

PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the corresponding
       Linux manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

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, which shall
       include 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 <sys/uio.h> header shall define the ssize_t and size_t types 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 POSIX.1‐2017, read(), readv(), write(),
       writev()

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2017			 sys_uio.h(0P)