147 lines
4.2 KiB
Groff
147 lines
4.2 KiB
Groff
.\" $NetBSD: bufq.9,v 1.5 2003/01/19 21:25:42 atatat Exp $
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.\"
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.\" Copyright (c) 2002 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 Juergen Hannken-Illjes.
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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 FOUNDATION OR CONTRIBUTORS
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.\" BE 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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.Dd July 16, 2002
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.Dt BUFQ 9
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.Os
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.Sh NAME
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.Nm bufq ,
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.Nm bufq_state ,
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.Nm bufq_alloc ,
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.Nm bufq_free ,
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.Nm BUFQ_PUT ,
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.Nm BUFQ_GET ,
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.Nm BUFQ_PEEK
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.Nd device buffer queues
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.Sh SYNOPSIS
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.Fd #include \*[Lt]buf.h\*[Gt]
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.Ft void
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.Fn bufq_alloc "struct bufq_state *bufq" "int flags"
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.Ft void
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.Fn bufq_free "struct bufq_state *bufq"
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.Ft void
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.Fn BUFQ_PUT "struct bufq_state *bufq" "struct buf *bp"
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.Ft "struct buf *"
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.Fn BUFQ_GET "struct bufq_state *bufq"
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.Ft "struct buf *"
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.Fn BUFQ_PEEK "struct bufq_state *bufq"
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.Sh DESCRIPTION
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The
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.Nm
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subsystem is a set of operations for the management of device buffer queues.
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.Pp
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The primary data type for using the operations is the
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.Em bufq_state
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structure in
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.Pa buf.h :
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.Bd -literal
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struct bufq_state {
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void (*bq_put)(struct bufq_state *, struct buf *);
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struct buf *(*bq_get)(struct bufq_state *, int);
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void *bq_private;
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int bq_flags; /* Flags from bufq_alloc() */
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};
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.Ed
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.Pp
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Valid values for the
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.Em flags
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argument are:
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.Pp
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.Bl -tag -offset indent -width BUFQ_SORT_RAWBLOCK -compact
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.It Dv BUFQ_SORT_RAWBLOCK
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sort by
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.Em b_rawblkno
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.It Dv BUFQ_SORT_CYLINDER
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sort by
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.Em b_cylinder
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and then by
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.Em b_rawblkno
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.It Dv BUFQ_FCFS
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queue strategy is first-come first-serve
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.It Dv BUFQ_DISKSORT
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queue strategy is min seek sort
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.It Dv BUFQ_READ_PRIO
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queue strategy is min seek sort for writes and first-come first-serve
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for reads with read priority
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.El
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.Sh FUNCTIONS
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.Bl -tag -width compact
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.It Fn bufq_alloc "bufq" "flags"
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Initialize a
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.Em bufq_state
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descriptor.
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The argument
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.Fa flags
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controls the strategy and sort order.
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.It Fn bufq_free "bufq"
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Destroy a
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.Em bufq_state
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descriptor.
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.It Fn BUFQ_PUT "bufq" "bp"
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Put the buf
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.Fa bp
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in the queue.
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.It Fn BUFQ_GET "bufq"
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Get the next buf from the queue and remove it from the queue.
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Returns
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.Dv NULL
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if the queue is empty.
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.It Fn BUFQ_PEEK "bufq"
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Get the next buf from the queue without removal.
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The next buf will remain the same until
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.Fn BUFQ_GET
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is called.
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Returns
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.Dv NULL
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if the queue is empty.
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.El
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.Sh CODE REFERENCES
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The actual code implementing the device buffer queues can be found
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in the file
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.Pa sys/kern/subr_disk.c .
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.Sh HISTORY
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The
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.Nm
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subsystem appeared in
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.Nx 2.0 .
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.Sh AUTHORS
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The
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.Nm
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subsystem was written by
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.if t .An J\(:urgen Hannken-Illjes
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.if n .An Juergen Hannken-Illjes
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.Aq hannken@NetBSD.org .
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