clear_active_bhs(active);
下面是一段 内核机制 的代码,在里面有一个clear_active_bhs(active);
请问这个函数是做什么用的?
我自己也没有找到声明的地方，请赐教！
/*
* linux/kernel/softirq.c
*
* Copyright (C) 1992 Linus Torvalds
*
* do_bottom_half() runs at normal kernel priority: all interrupts
* enabled.do_bottom_half() is atomic with respect to itself: a
* bottom_half handler need not be re-entrant.
*
* Fixed a disable_bh()/enable_bh() race (was causing a console lockup)
* due bh_mask_count not atomic handling. Copyright (C) 1998Andrea Arcangeli
*/
#include <linux/mm.h>
#include <linux/kernel_stat.h>
#include <linux/interrupt.h>
#include <linux/smp_lock.h>
#include <asm/io.h>
/* intr_count died a painless death... -DaveM */
atomic_t bh_mask_count[32];
unsigned long bh_active = 0;
unsigned long bh_mask = 0;
void (*bh_base[32])(void);
/*
* This needs to make sure that only one bottom half handler
* is ever active at a time. We do this without locking by
* doing an atomic increment on the intr_count, and checking
* (nonatomically) against 1. Only if it's 1 do we schedule
* the bottom half.
*
* Note that the non-atomicity of the test (as opposed to the
* actual update) means that the test may fail, and _nobody_
* runs the handlers if there is a race that makes multiple
* CPU's get here at the same time. That's ok, we'll run them
* next time around.
*/
static inline void run_bottom_halves(void)
{
unsigned long active;
void (**bh)(void);
active = get_active_bhs();
clear_active_bhs(active);
bh = bh_base;
do {
if (active & 1)
(*bh)();
bh++;
active >>= 1;
} while (active);
}
asmlinkage void do_bottom_half(void)
{
int cpu = smp_processor_id();
if (softirq_trylock(cpu)) {
if (hardirq_trylock(cpu)) {
__sti();
run_bottom_halves();
__cli();
hardirq_endlock(cpu);
}
softirq_endlock(cpu);
}
}
this is defined in 2.2 kernel and removed from 2.4 kernel.
is this dicussed in ulk 1st edition?
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