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.1‐2008, read(), readv(), write(), writev()

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1,  2013  Edition,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013  by  the
       Institute  of  Electrical  and  Electronics  Engineers,  Inc and The Open Group.  (This is
       POSIX.1-2008 with the  2013  Technical  Corrigendum  1  applied.)  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.unix.org/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 .