diff options
author | jhb <jhb@FreeBSD.org> | 2001-03-28 07:30:58 +0000 |
---|---|---|
committer | jhb <jhb@FreeBSD.org> | 2001-03-28 07:30:58 +0000 |
commit | 640834f7558f623ad0342c1a1afeb33ccd8e3586 (patch) | |
tree | 580e4b79a4a804fb53e7b04e75fa1c7e90909db0 /share/man/man9/critical_enter.9 | |
parent | 1f6d026436e51c7317cd4d918a8f7759281c9471 (diff) | |
download | FreeBSD-src-640834f7558f623ad0342c1a1afeb33ccd8e3586.zip FreeBSD-src-640834f7558f623ad0342c1a1afeb33ccd8e3586.tar.gz |
Add a manpage for the critical_enter/exit() functions.
Diffstat (limited to 'share/man/man9/critical_enter.9')
-rw-r--r-- | share/man/man9/critical_enter.9 | 97 |
1 files changed, 97 insertions, 0 deletions
diff --git a/share/man/man9/critical_enter.9 b/share/man/man9/critical_enter.9 new file mode 100644 index 0000000..e288678 --- /dev/null +++ b/share/man/man9/critical_enter.9 @@ -0,0 +1,97 @@ +.\" Copyright (c) 2001 John H. Baldwin <jhb@FreeBSD.org> +.\" 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, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, 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 AUTHOR AND CONTRIBUTORS ``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 AUTHOR OR CONTRIBUTORS 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 March 22, 2001 +.Dt CRITICAL_ENTER 9 +.Os +.Sh NAME +.Nm critical_enter , +.Nm critical_exit +.Nd enter and exit a critical region +.Sh SYNOPSIS +.Fd #include <sys/types.h> +.Fd #include <sys/systm.h> +.Ft critical_t +.Fn critical_enter "void" +.Ft void +.Fn critical_exit "critical_t savecrit" +.Sh DESCRIPTION +These functions are used to prevent preemption in a critcal region of code. +All that is guaranteed is that the current CPU will not be preempted by an +external interrupt. +The current CPU may still trigger faults and exceptions during a critical +section. +The +.Fn critical_enter +function returns an opaque value of type +.Vt critical_t . +This value must be passed to the +.Fn critical_exit +function when leaving the critical region. +.Pp +Note that these functions are not required to provide any inter-CPU +synchronization, data protection, or memory ordering guarantees and thus +should +.Sy not +be used to protect shared data structures. +.Pp +These functions should be used with care as an infinite loop within a +critical region will deadlock the CPU. +.Sh RETURN VALUES +The +.Fn critical_enter +function returns an opaque value that must be passed to a corresponding call to +.Fn critical_exit . +.Sh EXAMPLES +This example demonstrates the use of +.Fn critical_enter +and +.Fn critical_exit +to guarantee atomic access to the DMA controller. +.Bd -literal -offset indent +int +isa_dmastatus(int chan) +{ + u_long cnt = 0; + int ffport, waport; + u_long low1, high1, low2, high2; + critical_t savecrit; + + ... + savecrit = critical_enter(); + outb(ffport, 0); + low1 = inb(waport); + high1 = inb(waport); + outb(ffport, 0); + low2 = inb(waport); + high2 = inb(waport); + critical_exit(savecrit); + ... +} +.Ed +.Sh HISTORY +These functions were introduced in +.Fx 5.0 . |