164 lines
5.0 KiB
Groff
164 lines
5.0 KiB
Groff
.\" $NetBSD: spl.9,v 1.4 1997/11/20 05:47:42 mikel Exp $
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.\"
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.\" Copyright (c) 1997 Michael Long.
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.\" Copyright (c) 1997 Jonathan Stone.
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.\" All rights reserved.
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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. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd March 11, 1997
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.Dt SPL 9
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.Os NetBSD
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.Sh NAME
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.Nm spl ,
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.Nm spl0 ,
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.Nm splbio ,
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.Nm splclock ,
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.Nm splhigh ,
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.Nm splimp ,
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.Nm splnet ,
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.Nm splsched ,
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.Nm splserial ,
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.Nm splsoftclock ,
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.Nm splsoftnet ,
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.Nm splsoftserial ,
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.Nm splstatclock ,
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.Nm spltty ,
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.Nm splx
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.Nd modify system interrupt priority level
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.Sh SYNOPSIS
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.Fd #include <machine/intr.h>
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.Ft int
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.Fn splhigh void
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.Ft int
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.Fn splsched void
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.Ft int
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.Fn splserial void
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.Ft int
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.Fn splclock void
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.Ft int
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.Fn splstatclock void
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.Ft int
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.Fn splimp void
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.Ft int
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.Fn spltty void
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.Ft int
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.Fn splsoftserial void
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.Ft int
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.Fn splnet void
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.Ft int
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.Fn splbio void
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.Ft int
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.Fn splsoftnet void
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.Ft int
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.Fn splsoftclock void
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.Ft int
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.Fn spl0 void
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.Ft void
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.Fn splx "int s"
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.Sh DESCRIPTION
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These functions raise and lower the system priority level.
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They are used by kernel code to block interrupts with priority less
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than or equal to the named level (e.g.
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.Fn spltty
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blocks interrupts of priority less than or equal to
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.Dv IPL_TTY Ns ).
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The code may then safely access variables or data structures which are
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read or modified by interrupt service routines that run at the named
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level.
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.Pp
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A
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.Nm
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function exists for each distinct priority level which can exist in
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the system. These functions and the corresponding priority levels are
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used for various defined purposes, and may be divided into two main
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types: hard and soft. Hard interrupts are generated by hardware
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devices. Soft interrupts are generated by callouts, and are called
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from the kernel's periodic timer interrupt service routine.
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.Pp
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In order of highest to lowest priority, the priority-raising functions
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are:
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.Bl -tag -width splsoftserialXX
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.It Fn splhigh
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blocks all hard and soft interrupts. It is used for code that cannot
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tolerate any interrupts, like hardware context switching code and
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the
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.Xr ddb 4
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in-kernel debugger.
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.It Fn splserial
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blocks hard interrupts from serial interfaces. Code running at this
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level may not access the tty subsystem.
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.It Fn splsched
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blocks interrupts that may access scheduler data structures. Code
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running at or above this level may not call
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.Fn sleep ,
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.Fn tsleep ,
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or
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.Fn wakeup ,
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nor may it post signals.
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.It Fn splclock
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blocks the hardware clock interrupt. It is used by
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.Fn hardclock
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to update kernel and process times, and must be used by any other code
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that accesses time-related data.
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.It Fn splstatclock
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blocks the hardware statistics clock interrupt. It is used by
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.Fn statclock
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to update kernel profiling and other statistics, and must be used by
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any code that accesses that data.
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This level is identical to
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.Fn splclock
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if there is no separate statistics clock.
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.It Fn splimp
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blocks hard interrupts from all devices that are allowed to use the
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kernel
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.Xr malloc 9 .
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That includes all disk, network, and tty device interrupts.
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.It Fn spltty
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blocks hard interrupts from TTY devices.
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.It Fn splsoftserial
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blocks soft interrupts generated by serial devices.
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.It Fn splnet
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blocks hard interrupts from network interfaces.
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.It Fn splbio
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blocks hard interrupts from disks and other mass-storage devices.
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.It Fn splsoftnet
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blocks soft network interrupts.
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.El
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.Pp
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Two functions lower the system priority level. They are:
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.Bl -tag -width splsoftclockXX
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.It Fn splsoftclock
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unblocks all interrupts but the soft clock interrupt.
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.It Fn spl0
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unblocks all interrupts.
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.El
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.Pp
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The
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.Fn splx
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function restores the system priority level to the one encoded in
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.Fa s ,
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which must be a value previously returned by one of the other
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.Nm
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functions.
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