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.\" $OpenBSD: uiomove.9,v 1.19 2016/03/15 06:49:21 jmc Exp $
.\" $NetBSD: uiomove.9,v 1.6 2001/12/26 00:16:30 wiz Exp $
.\"
.\" Copyright (c) 1996 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd $Mdocdate: March 15 2016 $
.Dt UIOMOVE 9
.Os
.Sh NAME
.Nm uiomove
.Nd move data described by a struct uio
.Sh SYNOPSIS
.In sys/systm.h
.Ft int
.Fn uiomove "void *buf" "size_t n" "struct uio *uio"
.Sh DESCRIPTION
The
.Nm
function copies up to
.Fa n
bytes between the kernel-space address pointed
to by
.Fa buf
and the addresses described by
.Fa uio ,
which may be in user-space or kernel-space.
.Pp
The
.Fa uio
argument is a pointer to a
.Fa struct uio
as defined by
.In sys/uio.h :
.Bd -literal
struct uio {
struct iovec *uio_iov; /* pointer to array of iovecs */
int uio_iovcnt; /* number of iovecs in array */
off_t uio_offset; /* offset into file this uio corresponds to */
size_t uio_resid; /* residual i/o count */
enum uio_seg uio_segflg;
enum uio_rw uio_rw;
struct proc *uio_procp;/* associated process or NULL */
};
.Ed
.Pp
A
.Fa struct uio
typically describes data in motion.
Several of the fields described below reflect that expectation.
.Bl -tag -width uio_xxxxxx
.It uio_iov
Pointer to array of
.Fa struct iovecs :
.Bd -literal
struct iovec {
void *iov_base; /* Base address. */
size_t iov_len; /* Length. */
};
.Ed
.It uio_iovcnt
The number of iovecs in the array.
.It uio_offset
An offset into the corresponding object.
.It uio_resid
The amount of data remaining to be transferred.
.It uio_segflg
A flag indicating whether the space described is in user-space
(UIO_USERSPACE) or kernel-space (UIO_SYSSPACE).
.It uio_rw
A flag indicating whether data should be read into the space
(UIO_READ) or written from the space (UIO_WRITE).
.It uio_procp
A pointer to a process whose data area is described by the
structure, or which is having the I/O done on its behalf if
the area is in kernel-space.
.Nm uiomove
itself does not use this field if the area is in kernel-space,
but other functions that take a
.Fa struct uio
may depend on this information.
.El
.Pp
The value of
.Fa uio->uio_rw
controls whether
.Nm
copies data from
.Fa buf
to
.Fa uio
or vice versa.
.Pp
The lesser of
.Fa n
or
.Fa uio->uio_resid
bytes are copied.
.Pp
.Nm
changes fields of the structure pointed to by
.Fa uio ,
such that
.Fa uio->uio_resid
is decremented by the amount of data moved,
.Fa uio->uio_offset
is incremented by the same amount, and the array of iovecs is adjusted
to point that much farther into the region described.
This allows multiple calls to
.Nm
to easily be used to fill or drain the region of data.
.Sh RETURN VALUES
.Nm
returns 0 on success or EFAULT if a bad address is encountered.
.Sh SEE ALSO
.Xr copy 9
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