239 lines
6.2 KiB
Groff
239 lines
6.2 KiB
Groff
.\" $NetBSD: bufq.9,v 1.22 2016/11/18 08:29:43 wiz 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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.\"
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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 November 17, 2016
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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_init ,
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.Nm bufq_register ,
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.Nm bufq_unregister ,
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.Nm bufq_state ,
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.Nm bufq_alloc ,
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.Nm bufq_drain ,
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.Nm bufq_free ,
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.Nm bufq_getstrategyname ,
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.Nm bufq_move ,
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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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.Nm bufq_cancel
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.Nd device buffer queues
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.Sh SYNOPSIS
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.In sys/bufq.h
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.Ft void
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.Fn bufq_init "void"
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.Ft int
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.Fn bufq_register "struct bufq_strat *"
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.Ft int
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.Fn bufq_unregister "struct bufq_strat *"
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.Ft int
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.Fn bufq_alloc "struct bufq_state **bufq" "const char *strategy" "int flags"
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.Ft void
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.Fn bufq_drain "struct bufq_state *bufq"
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.Ft void
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.Fn bufq_free "struct bufq_state *bufq"
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.Ft "const char *"
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.Fn bufq_getstrategyname "struct bufq_state *bufq"
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.Ft void
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.Fn bufq_move "struct bufq_state *dst" "struct bufq_state *src"
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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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.Ft "struct buf *"
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.Fn bufq_cancel "struct bufq_state *bufq" "struct buf *bp"
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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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Various strategies for ordering of entries in the buffer queues can be
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provided by loadable kernel modules (see
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.Xr module 9 ) .
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By default, the
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.Dv BUFQ_FCFS
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and
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.Dv BUFQ_DISKSORT
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strategies are included in
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the kernel; see
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.Xr options 4
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for more details.
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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, which is opaque for users.
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Each buffer queue strategy module is defined by the
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.Em bufq_strat
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structure, which is also opaque for users.
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.Sh FUNCTIONS
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.Bl -tag -width compact
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.It Fn bufq_init "void"
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Initialize the
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.Nm
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subsystem.
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This routine must be called before any other
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.Nm
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routines.
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.It Fn bufq_register "bs"
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Registers the specified buffer queue strategy module so it can be used
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in subsequent operations.
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.It Fn bufq_unregister "bs"
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Unregisters the specified buffer queue strategy module.
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The routine will fail if any buffer queues for the specified strategy
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are in use (see
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.Fn bufq_alloc
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below).
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.It Fn bufq_alloc "bufq" "strategy" "flags"
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Allocate and initialize a
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.Em bufq_state
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descriptor.
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.Pp
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The argument
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.Fa strategy
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specifies a buffer queue strategy to be used for this buffer queue.
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The following special values can be used:
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.Pp
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.Bl -tag -offset indent -width BUFQ_DISK_DEFAULT_STRAT -compact
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.It Dv BUFQ_STRAT_ANY
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Let
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.Fn bufq_alloc
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select a strategy.
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.It Dv BUFQ_DISK_DEFAULT_STRAT
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Let
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.Fn bufq_alloc
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select a strategy, assuming it will be used for a normal disk device.
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.El
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.Pp
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Valid bits for the
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.Fa flags
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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_EXACT
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Fail if a strategy specified by
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.Fa strategy
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is not available.
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In that case,
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.Fa bufq_alloc
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returns
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.Dv ENOENT .
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If this flag is not specified,
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.Fn bufq_alloc
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will silently use one of available strategies.
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.El
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.Pp
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If a specific strategy is specified but not currently available, the
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.Nm bufq
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subsystem will attempt to auto-load the corresponding kernel module using
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.Xr module_autoload 9 .
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.It Fn bufq_drain "bufq"
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Drain a
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.Em bufq_state
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descriptor.
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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_getstrategyname "bufq"
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Get a strategy identifier of a buffer queue, the
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string returned will be NUL-terminated and it always
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will be a valid strategy name.
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.It Fn bufq_move "dst" "src"
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Move all requests from the buffer queue
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.Fa src
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to the buffer queue
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.Fa dst .
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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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.Fn bufq_put ,
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or
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.Fn bufq_drain
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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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.It Fn bufq_cancel "bufq" "bp"
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Cancel the buf
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.Fa bp
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issued earlier on the queue.
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Returns
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.Dv NULL
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if the element can not be found on the queue or
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.Fa bp
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if it has been found and removed.
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This operation can be computationally expensive if there are
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a lot of buffers queued.
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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_bufq.c .
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The code implementing specific buffer queue strategies can be found in
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the files
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.Pa sys/kern/bufq_*.c .
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.Sh NOTES
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A list of currently available buffer queue strategies is available via
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the
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.Dq kern.bufq.strategies
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.Xr sysctl 7
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variables.
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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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.An J\(:urgen Hannken-Illjes
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.Aq hannken@NetBSD.org .
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