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SPL(9) | Kernel Developer's Manual | SPL(9) |
NAME¶
splbio
,
splclock
,
splhigh
,
splimp
,
splnet
,
splsoftclock
,
splsofttty
,
splstatclock
,
spltty
,
splvm
,
spl0
,
splx
—
manipulate interrupt priorities
SYNOPSIS¶
#include
<sys/types.h>
#include
<sys/systm.h>
intrmask_t
splbio
(void);
intrmask_t
splclock
(void);
intrmask_t
splhigh
(void);
intrmask_t
splimp
(void);
intrmask_t
splnet
(void);
intrmask_t
splsoftclock
(void);
intrmask_t
splsofttty
(void);
intrmask_t
splstatclock
(void);
intrmask_t
spltty
(void);
void
spl0
(void);
void
splx
(intrmask_t
ipl);
DESCRIPTION¶
This API is deprecated. Use mutexes to protect data
structures instead. See mutex(9) for more
information. The API is now a complete NOP. This man page documents historical
behavior so you can understand the code locking that the spl did when
converting code from versions of the kernel prior to FreeBSD
5.0. The examples in this man page are also obsolete and should not be
viewed as documenting FreeBSD 5.0 and newer.
The spl
() function family sets the interrupt
priority “level” of the CPU. This prevents interrupt handlers of
the blocked priority level from being run. This is used in the
“synchronous” part of a driver (the part that runs on behalf of
the user process) to examine or modify data areas that might be examined or
modified by interrupt handlers.
Each driver that uses interrupts is normally assigned to an interrupt priority
group by a keyword in its config line. For example:
device foo0 at isa? port 0x0815 irq 12 tty
xxx
()
The function splx
() sets the interrupt
priority to an absolute value. The intent is that the value returned by the
other functions should be saved in a local variable, and later passed to
splx
() in order to restore the previous
priority.
The function spl0
() lowers the priority to a
value where all interrupt handlers are unblocked, but ASTs (asynchronous
system traps) remain blocked until the system is about to return to user mode.
The traditional assignment of the various device drivers to the interrupt
priority groups can be roughly classified as:
splnet
()- Software part of the network interface drivers.
splimp
()- All network interface drivers.
splbio
()- All buffered IO (i.e., disk and the like) drivers.
spltty
()- Basically, all non-network communications devices, but effectively used for all drivers that are neither network nor disks.
RETURN VALUES¶
All functions exceptsplx
() and
spl0
() return the previous priority value.
EXAMPLES¶
This is a typical example demonstrating the usage:struct foo_softc { ... int flags; #define FOO_ASLEEP 1 #define FOO_READY 2 } foo_softc[NFOO]; int foowrite(...) { struct foo_softc *sc; int s, error; ... s = spltty(); if (!(sc->flags & FOO_READY)) { /* Not ready, must sleep on resource. */ sc->flags |= FOO_ASLEEP; error = tsleep(sc, PZERO, "foordy", 0); sc->flags &= ~FOO_ASLEEP; } sc->flags &= ~FOO_READY; splx(s); ... } void foointr(...) { struct foo_softc *sc; ... sc->flags |= FOO_READY; if (sc->flags & FOO_ASLEEP) /* Somebody was waiting for us, awake him. */ wakeup(sc); ... }
HISTORY¶
The interrupt priority levels appeared in a very early version of UNIX. They have been traditionally known by number instead of by names, and were inclusive up to higher priority levels (i.e., priority 5 has been blocking everything up to level 5). This is no longer the case in FreeBSD. The traditional name ‘level
’ for them is still reflected in
the letter ‘l
’ of the respective
functions and variables, although they are not really levels anymore, but
rather different (partially inclusive) sets of functions to be blocked during
some periods of the life of the system. The historical number scheme can be
considered as a simple linearly ordered set of interrupt priority groups.
FreeBSD 5.0 eliminated spl entirely in favor of locking
primitives which scale to more than one processor.
AUTHORS¶
This manual page was written by Jörg Wunsch.July 21, 1996 | Debian |