✏ EDIT: uio.h

/* Copyright (C) 1991-2018 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#ifndef _SYS_UIO_H
#define _SYS_UIO_H	1

#include <features.h>
#include <sys/types.h>
#include <bits/types/struct_iovec.h>
#include <bits/uio_lim.h>
#ifdef __IOV_MAX
# define UIO_MAXIOV __IOV_MAX
#else
# undef UIO_MAXIOV
#endif

__BEGIN_DECLS

/* Read data from file descriptor FD, and put the result in the
   buffers described by IOVEC, which is a vector of COUNT 'struct iovec's.
   The buffers are filled in the order specified.
   Operates just like 'read' (see <unistd.h>) except that data are
   put in IOVEC instead of a contiguous buffer.

This function is a cancellation point and therefore not marked with
   __THROW.  */
extern ssize_t readv (int __fd, const struct iovec *__iovec, int __count)
  __wur;

/* Write data pointed by the buffers described by IOVEC, which
   is a vector of COUNT 'struct iovec's, to file descriptor FD.
   The data is written in the order specified.
   Operates just like 'write' (see <unistd.h>) except that the data
   are taken from IOVEC instead of a contiguous buffer.

This function is a cancellation point and therefore not marked with
   __THROW.  */
extern ssize_t writev (int __fd, const struct iovec *__iovec, int __count)
  __wur;

#ifdef __USE_MISC
# ifndef __USE_FILE_OFFSET64
/* Read data from file descriptor FD at the given position OFFSET
   without change the file pointer, and put the result in the buffers
   described by IOVEC, which is a vector of COUNT 'struct iovec's.
   The buffers are filled in the order specified.  Operates just like
   'pread' (see <unistd.h>) except that data are put in IOVEC instead
   of a contiguous buffer.

This function is a cancellation point and therefore not marked with
   __THROW.  */
extern ssize_t preadv (int __fd, const struct iovec *__iovec, int __count,
		       __off_t __offset) __wur;

/* Write data pointed by the buffers described by IOVEC, which is a
   vector of COUNT 'struct iovec's, to file descriptor FD at the given
   position OFFSET without change the file pointer.  The data is
   written in the order specified.  Operates just like 'pwrite' (see
   <unistd.h>) except that the data are taken from IOVEC instead of a
   contiguous buffer.

This function is a cancellation point and therefore not marked with
   __THROW.  */
extern ssize_t pwritev (int __fd, const struct iovec *__iovec, int __count,
			__off_t __offset) __wur;

# else
#  ifdef __REDIRECT
extern ssize_t __REDIRECT (preadv, (int __fd, const struct iovec *__iovec,
				    int __count, __off64_t __offset),
			   preadv64) __wur;
extern ssize_t __REDIRECT (pwritev, (int __fd, const struct iovec *__iovec,
				     int __count, __off64_t __offset),
			   pwritev64) __wur;
#  else
#   define preadv preadv64
#   define pwritev pwritev64
#  endif
# endif

# ifdef __USE_LARGEFILE64
/* Read data from file descriptor FD at the given position OFFSET
   without change the file pointer, and put the result in the buffers
   described by IOVEC, which is a vector of COUNT 'struct iovec's.
   The buffers are filled in the order specified.  Operates just like
   'pread' (see <unistd.h>) except that data are put in IOVEC instead
   of a contiguous buffer.

This function is a cancellation point and therefore not marked with
   __THROW.  */
extern ssize_t preadv64 (int __fd, const struct iovec *__iovec, int __count,
			 __off64_t __offset) __wur;

This function is a cancellation point and therefore not marked with
   __THROW.  */
extern ssize_t pwritev64 (int __fd, const struct iovec *__iovec, int __count,
			  __off64_t __offset) __wur;
# endif
#endif	/* Use misc.  */

#ifdef __USE_GNU
# ifndef __USE_FILE_OFFSET64
/* Same as preadv but with an additional flag argumenti defined at uio.h.  */
extern ssize_t preadv2 (int __fp, const struct iovec *__iovec, int __count,
			__off_t __offset, int ___flags) __wur;

/* Same as preadv but with an additional flag argument defined at uio.h.  */
extern ssize_t pwritev2 (int __fd, const struct iovec *__iodev, int __count,
			 __off_t __offset, int __flags) __wur;

# else
#  ifdef __REDIRECT
extern ssize_t __REDIRECT (pwritev2, (int __fd, const struct iovec *__iovec,
				      int __count, __off64_t __offset,
				      int __flags),
			   pwritev64v2) __wur;
extern ssize_t __REDIRECT (preadv2, (int __fd, const struct iovec *__iovec,
				     int __count, __off64_t __offset,
				     int __flags),
			   preadv64v2) __wur;
#  else
#   define preadv2 preadv64v2
#   define pwritev2 pwritev64v2
#  endif
# endif

# ifdef __USE_LARGEFILE64
/* Same as preadv but with an additional flag argumenti defined at uio.h.  */
extern ssize_t preadv64v2 (int __fp, const struct iovec *__iovec,
			   int __count, __off64_t __offset,
			   int ___flags) __wur;

/* Same as preadv but with an additional flag argument defined at uio.h.  */
extern ssize_t pwritev64v2 (int __fd, const struct iovec *__iodev,
			    int __count, __off64_t __offset,
			    int __flags) __wur;
# endif
#endif /* Use GNU.  */

__END_DECLS

/* Some operating systems provide system-specific extensions to this
   header.  */
#ifdef __USE_GNU
# include <bits/uio-ext.h>
#endif

#endif /* sys/uio.h */

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