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 .