mirror of
https://git.FreeBSD.org/src.git
synced 2024-12-24 11:29:10 +00:00
133 lines
3.8 KiB
Groff
133 lines
3.8 KiB
Groff
.\"
|
|
.\" Copyright (C) 2001 Chad David <davidc@acns.ab.ca>. All rights reserved.
|
|
.\"
|
|
.\" 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(s), this list of conditions and the following disclaimer as
|
|
.\" the first lines of this file unmodified other than the possible
|
|
.\" addition of one or more copyright notices.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice(s), 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 COPYRIGHT HOLDER(S) ``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 COPYRIGHT HOLDER(S) 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.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd July 9, 2001
|
|
.Dt PBUF 9
|
|
.Os
|
|
.Sh NAME
|
|
.Nm pbuf ,
|
|
.Nm getpbuf ,
|
|
.Nm trypbuf ,
|
|
.Nm relpbuf
|
|
.Nd "functions for managing physical buffers"
|
|
.Sh SYNOPSIS
|
|
.In sys/param.h
|
|
.In sys/systm.h
|
|
.In sys/bio.h
|
|
.In sys/buf.h
|
|
.Ft "struct buf *"
|
|
.Fn getpbuf "int *pfreecnt"
|
|
.Ft "struct buf *"
|
|
.Fn trypbuf "int *pfreecnt"
|
|
.Ft void
|
|
.Fn relpbuf "struct buf *bp" "int *pfreecnt"
|
|
.Sh DESCRIPTION
|
|
These functions are used to allocate and release physical buffers.
|
|
.Pp
|
|
The physical buffers are allocated at system startup and are
|
|
maintained in a separate pool from the main system buffers.
|
|
They are intended for use by subsystems that cannot or should not be
|
|
reliant on the main pool of buffers (for example the swap pager).
|
|
The system allocates between 16 and 256 physical buffers depending
|
|
on the amount of memory in the system.
|
|
.Pp
|
|
Each subsystem that allocates buffers via these calls is expected
|
|
to manage its own percentage free counter.
|
|
If the value is initialized to \-1 the number of buffers available
|
|
to the subsystem is limited only by the number of physical buffers
|
|
available.
|
|
The number of buffers is stored in
|
|
.Va nswbuf
|
|
which is defined in
|
|
.Pa sys/buf.h
|
|
and initialized in
|
|
.Fn cpu_startup .
|
|
A recommended initialization value is 1/2
|
|
.Va nswbuf .
|
|
.Pp
|
|
The
|
|
.Fn getpbuf
|
|
function returns the first available buffer to the user.
|
|
If there are no buffers available,
|
|
.Fn getpbuf
|
|
will sleep waiting for one to become available.
|
|
If
|
|
.Fa pfreecnt
|
|
is zero,
|
|
.Fn getpbuf
|
|
will sleep until it increases.
|
|
.Fa pfreecnt
|
|
is decremented prior to returning.
|
|
.Pp
|
|
The
|
|
.Fn trypbuf
|
|
function returns the first available buffer.
|
|
If there are no buffers available,
|
|
.Dv NULL
|
|
is returned.
|
|
As well, if
|
|
.Fa pfreecnt
|
|
is zero,
|
|
.Dv NULL
|
|
is returned.
|
|
.Fa pfreecnt
|
|
is decremented prior to returning a valid buffer.
|
|
If
|
|
.Dv NULL
|
|
is returned,
|
|
.Fa pfreecnt
|
|
is not modified.
|
|
.Pp
|
|
The
|
|
.Fn relpbuf
|
|
function releases the buffer back to the free list.
|
|
If the buffers
|
|
.Va b_rcred
|
|
or
|
|
.Va b_wcred
|
|
structures are not
|
|
.Dv NULL ,
|
|
they are freed.
|
|
See
|
|
.Xr crfree 9 .
|
|
.Pp
|
|
.Fa pfreecnt
|
|
is incremented prior to returning.
|
|
.Sh RETURN VALUES
|
|
.Fn getpbuf
|
|
and
|
|
.Fn trypbuf
|
|
return a pointer to the buffer.
|
|
In the case of
|
|
.Fn trypbuf ,
|
|
.Dv NULL
|
|
can also be returned indicating that there are no buffers available.
|
|
.Sh AUTHORS
|
|
This manual page was written by
|
|
.An Chad David Aq davidc@acns.ab.ca .
|