"luwei (O)" <luwei32@xxxxxxxxxx> writes:
> 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 ?
The callback just needs to reschedule itself by calling
bpf_timer_start() again before exiting... :)
-Toke
