These functions raise and lower the interrupt priority level on i386. They are used by machine-dependent kernel code to implement the machine-independent
spl(9) interface.
In a multi-CPU system, these functions change the interrupt priority level on the local CPU only. In general, device drivers should not make use of these functions.
The
spllower() function sets the system priority level to the one encoded in
s, if
s is lower than the current level. Otherwise, it does not change the level. Use
splx() instead of
spllower(), except in extraordinary circumstances.
The
splraise() function sets the system priority level to the one encoded in
s, if
s is greater than the current level, and returns the previous level. Otherwise, it does not change the level, and it returns the current level. Except in extraordinary circumstances, do not use
splraise(). Use one of the priority-raising functions defined in
spl(9), instead.