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 .