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Date: Wed, 22 Jul 2015 18:14:43 -0700 From: Alexei Starovoitov <ast@...mgrid.com> To: Kaixu Xia <xiakaixu@...wei.com>, davem@...emloft.net, acme@...nel.org, mingo@...hat.com, a.p.zijlstra@...llo.nl, masami.hiramatsu.pt@...achi.com, jolsa@...nel.org Cc: wangnan0@...wei.com, linux-kernel@...r.kernel.org, pi3orama@....com, hekuang@...wei.com Subject: Re: [PATCH v2 4/5] bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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