On 7/22/15 1:09 AM, Kaixu Xia wrote:
According to the perf_event_map_fd and key, the function
bpf_perf_event_read() can convert the corresponding map
value to the pointer to struct perf_event and return the
Hardware PMU counter value.
The key can't be passed to bpf_perf_event_read() directly
because the function argument constraint is lacked.
I don't understand above sentence.
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 69a1f6b..e3bb181 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -250,6 +250,8 @@ enum bpf_func_id {
* Return: 0 on success
*/
BPF_FUNC_get_current_comm,
+
+ BPF_FUNC_perf_event_read, /* u64 bpf_perf_event_read(&map, &key)
*/
no need for extra empty line.
+
+static u64 bpf_perf_event_read(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+ struct bpf_map *map = (struct bpf_map *) (unsigned long) r1;
+ void *key = (void *) (unsigned long) r2;
+ struct perf_event *event;
+ void *ptr;
+
+ if (map->map_type != BPF_MAP_TYPE_PERF_EVENT_ARRAY)
+ return -EINVAL;
please check this statically in verifier instead of in run-time.
+
+ rcu_read_lock();
unnecessary.
+ ptr = map->ops->map_lookup_elem(map, key);
+ rcu_read_unlock();
+ if (!ptr || !(*(unsigned long *)ptr))
+ return -EBADF;
all these casts can be removed. First cast of 'r1' into
perf_event_array will be enough.
+const struct bpf_func_proto bpf_perf_event_read_proto = {
+ .func = bpf_perf_event_read,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_CONST_MAP_PTR,
+ .arg2_type = ARG_PTR_TO_MAP_KEY,
make it arg2_type = ARG_ANYTHING then you'll just index
into array the way prog_array does and similar to bpf_tail_call.
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