.\"	$OpenBSD: uiomove.9,v 1.14 2014/01/21 03:15:46 schwarze Exp $
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.Dd $Mdocdate: January 21 2014 $
.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" "int 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