141 lines
4.4 KiB
Groff
141 lines
4.4 KiB
Groff
.\" $NetBSD: physio.9,v 1.2 1996/11/11 00:05:12 lukem Exp $
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.\"
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.\" Copyright (c) 1996 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Paul Kranenburg.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE
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.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd June 15, 1996
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.Dt PHYSIO 9
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.Os
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.Sh NAME
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.Nm physio
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.Nd initiate I/O on raw devices
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.Sh SYNOPSIS
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.Fd #include <sys/param.h>
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.Fd #include <sys/systm.h>
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.Fd #include <sys/buf.h>
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.Ft int
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.Fn physio "dev_t dev" "struct uio *uio" "int ioflag"
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.Sh DESCRIPTION
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The
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.Fn physio
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is a helper function typically called from character device read and write
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routines to start I/O on a user process buffer.
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It calls back on the
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provided
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.Fa strategy
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routine one or more times to complete the transfer described by
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.Fa uio .
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The maximum amount of data to transfer with each call to
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.Fa strategy
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is determined by the
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.Fa minphys
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routine.
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Since
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.Fa uio
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normally describes user space addresses,
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.Fn physio
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needs to lock the process into memory. This is done by setting the
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.Dv P_PHYSIO
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flag on the process.
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.Fn physio
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always awaits the completion of the entire requested transfer before
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returning, unless an error condition is detected earlier.
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In all cases,
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the buffer passed in
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.Fa bp
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is locked (marked as
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.Dq busy )
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for the duration of the entire transfer.
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.Pp
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A break-down of the arguments follows:
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.Bl -tag -width indent
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.It Fa strategy
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The device strategy routine to call for each chunk of data to initiate
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device I/O.
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.It Fa bp
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The buffer to use with the strategy routine.
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The buffer flags will have
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.Dv B_BUSY ,
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and
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.Dv B_PHYS
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set when passed to the strategy routine.
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If
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.Dv NULL ,
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a buffer is allocated from a system pool.
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.It Fa dev
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The device number identifying the device to interact with.
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.It Fa flags
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Direction of transfer; the only valid settings are
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.Dv B_READ
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or
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.Dv B_WRITE .
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.It Fa minphys
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A device specific routine called to determine the maximum transfer size
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that the device's strategy routine can handle.
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.It Fa uio
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The description of the entire transfer as requested by the user process.
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Currently, the results of passing a
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.Fa uio
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structure with the
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.Sq uio_segflg
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set to anything other than
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.Dv UIO_USERSPACE ,
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are undefined.
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.El
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.Sh RETURN VALUES
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If successful
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.Fn physio
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returns 0.
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.Er EFAULT
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is returned if the address range described by
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.Fa uio
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is not accessible by the requesting process.
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.Fn physio
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will return any error resulting from calls to the device strategy routine,
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by examining the
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.Dv B_ERROR
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buffer flag and the
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.Va b_error
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field.
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Note that the actual transfer size may be less than requested by
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.Fa uio
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if the device signals an
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.Dq end of file
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condition.
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.Sh SEE ALSO
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.Xr read 2 ,
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.Xr write 2
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