.\"
.\" Copyright (c) 2005 The DragonFly Project.  All rights reserved.
.\"
.\" This code is derived from software contributed to The DragonFly Project
.\" by Hiten Pandya <hmp@backplane.com>.
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.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\"    distribution.
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.\"    contributors may be used to endorse or promote products derived
.\"    from this software without specific, prior written permission.
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.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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
.\" COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
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.\"	$NetBSD: physio.9,v 1.2 1996/11/11 00:05:12 lukem Exp $
.\"
.\" Copyright (c) 1996 The NetBSD Foundation, Inc.
.\" All rights reserved.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Paul Kranenburg.
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.\" modification, are permitted provided that the following conditions
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.\" 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.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"        This product includes software developed by the NetBSD
.\"        Foundation, Inc. and its contributors.
.\" 4. Neither the name of The NetBSD Foundation nor the names of its
.\"    contributors may be used to endorse or promote products derived
.\"    from this software without specific prior written permission.
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.\" 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 REGENTS 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.
.\"
.\" $FreeBSD: src/share/man/man9/physio.9,v 1.6.2.4 2001/12/17 11:30:18 ru Exp $
.\" $DragonFly: src/share/man/man9/physio.9,v 1.5 2008/11/09 10:59:14 swildner Exp $
.\"
.Dd November 9, 2008
.Dt PHYSIO 9
.Os
.Sh NAME
.Nm physread ,
.Nm physwrite
.Nd initiate I/O on raw devices
.Sh SYNOPSIS
.In sys/buf.h
.In sys/device.h
.Ft int
.Fn physread "struct dev_read_args *ap"
.Ft int
.Fn physwrite "struct dev_write_args *ap"
.Sh DESCRIPTION
.Fn Physread
and
.Fn physwrite
are helper functions typically called from character device read and write
routines to start I/O on a user process buffer.
They will call the
.Fn dev_dstrategy
routine one or more times depending on the size of transfer which is
described by the
.Fa ap
argument.
.Pp
The maximum amount of data transferable in one iteration of the
.Fn physread
and
.Fn physwrite
functions is determined by the maximum I/O size supported by the device
.Fa dev ,
otherwise the value of
.Dv MAXPHYS
is used.
Until the I/O operation is complete, the calling process or thread is
put to sleep with the wait message set to
.Ql "physstr" .
.Pp
The
.Fn physread
and
.Fn physwrite
functions always await the completion of the entire requested transfer
before returning, unless an error condition is detected earlier.
.Pp
The
.Fa ap
argument is a pointer to a
.Vt dev_read_args
or
.Vt dev_write_args
structure, as passed to
.Nm d_read
or
.Nm d_write .
.Sh RETURN VALUES
If successful
.Fn physread
and
.Fn physwrite
will return 0.
.Pp
The
.Va errno
value
.Er EFAULT
will be returned if the address range described by
.Fa uio
is not accessible by the calling process or thread.
.Pp
Note that the actual transfer size may be less than requested by
.Fa ap
if the device signals an
.Dq end of file
condition.
.Sh SEE ALSO
.Xr read 2 ,
.Xr write 2 ,
.Xr uio 9