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.\" $OpenBSD: physio.9,v 1.10 2019/12/06 11:09:47 mpi Exp $
.\" $NetBSD: physio.9,v 1.5 1999/03/16 00:40:47 garbled Exp $
.\"
.\" Copyright (c) 1996 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Paul Kranenburg.
.\"
.\" 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: December 6 2019 $
.Dt PHYSIO 9
.Os
.Sh NAME
.Nm physio
.Nd initiate I/O on raw devices
.Sh SYNOPSIS
.Ft int
.Fo physio
.Fa "void (*strategy)(struct buf *)"
.Fa "dev_t dev"
.Fa "int flags"
.Fa "void (*minphys)(struct buf *)"
.Fa "struct uio *uio"
.Fc
.Sh DESCRIPTION
.Fn physio
is a helper function typically called from character device read and write
routines to start I/O on a user process buffer.
It calls back on the provided
.Fa strategy
routine one or more times to complete the transfer described by
.Fa uio .
The maximum amount of data to transfer with each call to
.Fa strategy
is determined by the
.Fa minphys
routine.
Since
.Fa uio
normally describes user space addresses,
.Fn physio
needs to lock the appropriate data area into memory before each transaction
with
.Fa strategy
(see
.Xr uvm_vslock_device 9
and
.Xr uvm_vsunlock_device 9 ) .
.Fn physio
always awaits the completion of the entire requested transfer before
returning, unless an error condition is detected earlier.
.Pp
In all cases, a temporary buffer is allocated from a system pool.
This buffer will have the
.Dv B_BUSY ,
.Dv B_PHYS ,
and
.Dv B_RAW
flags set when passed to the strategy routine.
.Pp
A break-down of the arguments follows:
.Bl -tag -width indent
.It Fa strategy
The device strategy routine to call for each chunk of data to initiate
device I/O.
.It Fa dev
The device number identifying the device to interact with.
.It Fa flags
Direction of transfer; the only valid settings are
.Dv B_READ
or
.Dv B_WRITE .
.It Fa minphys
A device specific routine called to determine the maximum transfer size
that the device's strategy routine can handle.
.It Fa uio
The description of the entire transfer as requested by the user process.
Currently, the results of passing a
.Fa uio
structure with the
.Sq uio_segflg
set to anything other than
.Dv UIO_USERSPACE ,
are undefined.
.El
.Sh RETURN VALUES
If successful,
.Fn physio
returns 0.
.Er EFAULT
is returned if the address range described by
.Fa uio
is not accessible by the requesting process.
.Fn physio
will return any error resulting from calls to the device strategy routine,
by examining the
.Dv B_ERROR
buffer flag and the
.Sq b_error
field.
Note that the actual transfer size may be less than requested by
.Fa uio
if the device signals an
.Dq end of file
condition.
.Sh SEE ALSO
.Xr read 2 ,
.Xr write 2 ,
.Xr uvm_vslock 9 ,
.Xr uvm_vsunlock 9
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