NetBSD/share/man/man9/bufq.9

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