spl(D3)spl(D3)NAMEspl - block/allow interrupts on a processor
SYNOPSIS
#include <sys/ddi.h>
int splbase(void);
int spltimeout(void);
int spldisk(void);
int splstr(void);
int spltty(void);
int splhi(void);
int spl0(void);
int spl7(void);
void splx(int oldlevel);
Arguments
oldlevel Last set priority value (only splx has an input argument).
DESCRIPTION
The spl functions block or allow servicing of interrupts on the processor
on which the function is called.
Return Values
All spl functions except splx return the previous priority level for use
by splx.
USAGE
Hardware devices are assigned to interrupt priority levels depending on
the type of device. Each spl function which blocks interrupts is
associated with some machine dependent interrupt priority level and will
prevent interrupts occurring at or below this priority level from being
serviced on the processor on which the spl function is called.
On a multiprocessor system, interrupts may be serviced by more than one
processor and, therefore, use of a spl function alone is not sufficient
to prevent interrupt code from executing and manipulating driver data
structures during a critical section. Drivers that must prevent
execution of interrupt-level code in order to protect the integrity of
their data should use basic locks for this purpose [see LOCK_ALLOC(D3)].
The spl functions include the following:
splbase Block no interrupts. Should only be used by base-level code
that knows it is not nested within any section of protected
critical code.
spltimeout Block functions scheduled by itimeout and dtimeout.
spldisk Block disk device interrupts.
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spl(D3)spl(D3)
splstr Block STREAMS interrupts.
spltty Used by a TTY driver to protect critical code. spltty is
mapped to splstr.
splhi Block all interrupts. Can be used in any type of driver to
mask out all interrupts including the clock, and should be
used very sparingly.
spl0 Equivalent to splbase.
spl7 Equivalent to splhi.
To ensure driver portability, the named spl functions (such as splbase or
spltimeout) should be used whenever possible. The numbered spl functions
(spl0 and spl7) should be used only when an interrupt priority level must
be set to a specific value.
Calling a given spl function will block interrupts specified for that
function as well as interrupts at equal and lower levels. The notion of
low vs. high levels assumes a defined order of priority levels. The
following partial order is defined:
splbase <= spltimeout <= spldisk,splstr <= splhi
The ordering of spldisk and splstr relative to each other is not defined.
When setting a given priority level, the previous level returned should
be saved and splx or UNLOCK(D3) should be used as appropriate to restore
this level.
Interrupt-level code must never lower the interrupt priority level below
the level at which the interrupt handler was entered. For example, if an
interrupt handler is entered at the priority level associated with
spldisk, the handler must not call spltimeout.
Level
Base or Interrupt.
Synchronization Considerations
All spl functions do not sleep.
Driver-defined basic locks and read/write locks may be held across calls
to these functions, but the spl call must not cause the priority level to
be lowered below the level associated with the lock.
Driver-defined sleep locks may be held across calls to these functions.
REFERENCESLOCK(D3), LOCK_ALLOC(D3),
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