在 2021/7/2 3:20 AM, Alexei Starovoitov 写道:
From: Alexei Starovoitov <ast@xxxxxxxxxx>
Introduce 'struct bpf_timer { __u64 :64; __u64 :64; };' that can be embedded
in hash/array/lru maps as a regular field and helpers to operate on it:
// Initialize the timer.
// First 4 bits of 'flags' specify clockid.
// Only CLOCK_MONOTONIC, CLOCK_REALTIME, CLOCK_BOOTTIME are allowed.
long bpf_timer_init(struct bpf_timer *timer, struct bpf_map *map, int flags);
// Configure the timer to call 'callback_fn' static function.
long bpf_timer_set_callback(struct bpf_timer *timer, void *callback_fn);
// Arm the timer to expire 'nsec' nanoseconds from the current time.
long bpf_timer_start(struct bpf_timer *timer, u64 nsec, u64 flags);
// Cancel the timer and wait for callback_fn to finish if it was running.
long bpf_timer_cancel(struct bpf_timer *timer);
[...]
+static enum hrtimer_restart bpf_timer_cb(struct hrtimer *hrtimer)
+{
+ struct bpf_hrtimer *t = container_of(hrtimer, struct bpf_hrtimer, timer);
+ struct bpf_map *map = t->map;
+ void *value = t->value;
+ struct bpf_timer_kern *timer = value + map->timer_off;
+ struct bpf_prog *prog;
+ void *callback_fn;
+ void *key;
+ u32 idx;
+ int ret;
+
+ /* The triple underscore bpf_spin_lock is a direct call
+ * to BPF_CALL_1(bpf_spin_lock) which does irqsave.
+ */
+ ____bpf_spin_lock(&timer->lock);
+ /* callback_fn and prog need to match. They're updated together
+ * and have to be read under lock.
+ */
+ prog = t->prog;
+ callback_fn = t->callback_fn;
+
+ /* wrap bpf subprog invocation with prog->refcnt++ and -- to make
+ * sure that refcnt doesn't become zero when subprog is executing.
+ * Do it under lock to make sure that bpf_timer_start doesn't drop
+ * prev prog refcnt to zero before timer_cb has a chance to bump it.
+ */
+ bpf_prog_inc(prog);
+ ____bpf_spin_unlock(&timer->lock);
+
+ /* bpf_timer_cb() runs in hrtimer_run_softirq. It doesn't migrate and
+ * cannot be preempted by another bpf_timer_cb() on the same cpu.
+ * Remember the timer this callback is servicing to prevent
+ * deadlock if callback_fn() calls bpf_timer_cancel() on the same timer.
+ */
+ this_cpu_write(hrtimer_running, t);
+ if (map->map_type == BPF_MAP_TYPE_ARRAY) {
+ struct bpf_array *array = container_of(map, struct bpf_array, map);
+
+ /* compute the key */
+ idx = ((char *)value - array->value) / array->elem_size;
+ key = &idx;
+ } else { /* hash or lru */
+ key = value - round_up(map->key_size, 8);
+ }
+
+ ret = BPF_CAST_CALL(callback_fn)((u64)(long)map,
+ (u64)(long)key,
+ (u64)(long)value, 0, 0);
+ WARN_ON(ret != 0); /* Next patch moves this check into the verifier */
+ bpf_prog_put(prog);
+
+ this_cpu_write(hrtimer_running, NULL);
+ return HRTIMER_NORESTART;
+}
+
Your patch is awesome, and I tried your example and it works, my
call_back() is called after a certained time. But I am confued that
the bpf_timer_cb() function only returns HRTIMER_NORESTART,
how to trigger a periodic task, that means I want to call my call_back()
periodically, not just for one time ?
[...]
--
Best Regards,
Lu Wei
