1sys_uio.h(0P)              POSIX Programmer's Manual             sys_uio.h(0P)
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PROLOG

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

12       sys/uio.h — definitions for vector I/O operations
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SYNOPSIS

15       #include <sys/uio.h>
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DESCRIPTION

18       The <sys/uio.h> header shall define the iovec  structure,  which  shall
19       include at least the following members:
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22           void   *iov_base  Base address of a memory region for input or output.
23           size_t  iov_len   The size of the memory pointed to by iov_base.
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25       The <sys/uio.h> header uses the iovec structure for scatter/gather I/O.
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27       The  <sys/uio.h>  header  shall  define the ssize_t and size_t types as
28       described in <sys/types.h>.
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30       The following shall be declared as functions and may also be defined as
31       macros. Function prototypes shall be provided.
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34           ssize_t readv(int, const struct iovec *, int);
35           ssize_t writev(int, const struct iovec *, int);
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37       The following sections are informative.
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APPLICATION USAGE

40       The implementation can put a limit on the number of scatter/gather ele‐
41       ments which can be processed in one call. The symbol {IOV_MAX}  defined
42       in  <limits.h>  should always be used to learn about the limits instead
43       of assuming a fixed value.
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RATIONALE

46       Traditionally, the maximum number of scatter/gather elements the system
47       can  process in one call were described by the symbolic value {UIO_MAX‐
48       IOV}.  In IEEE Std 1003.1‐2001 this value is replaced by  the  constant
49       {IOV_MAX} which can be found in <limits.h>.
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FUTURE DIRECTIONS

52       None.
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SEE ALSO

55       <limits.h>, <sys_types.h>
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57       The System Interfaces volume of POSIX.1‐2017, read(), readv(), write(),
58       writev()
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61       Portions of this text are reprinted and reproduced in  electronic  form
62       from  IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
63       table Operating System Interface (POSIX), The Open Group Base  Specifi‐
64       cations  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of
65       Electrical and Electronics Engineers, Inc and The Open Group.   In  the
66       event of any discrepancy between this version and the original IEEE and
67       The Open Group Standard, the original IEEE and The Open Group  Standard
68       is  the  referee document. The original Standard can be obtained online
69       at http://www.opengroup.org/unix/online.html .
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71       Any typographical or formatting errors that appear  in  this  page  are
72       most likely to have been introduced during the conversion of the source
73       files to man page format. To report such errors,  see  https://www.ker‐
74       nel.org/doc/man-pages/reporting_bugs.html .
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78IEEE/The Open Group                  2017                        sys_uio.h(0P)
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