On Tue, Dec 05, 2017 at 10:31:28PM -0800, Yonghong Song wrote:
> Commit e87c6bc3852b ("bpf: permit multiple bpf attachments
> for a single perf event") added support to attach multiple
> bpf programs to a single perf event.
> Commit 2541517c32be ("tracing, perf: Implement BPF programs
> attached to kprobes") utilized the existing perf ioctl
> interface and added the command PERF_EVENT_IOC_SET_BPF
> to attach a bpf program to a tracepoint.
>
> This patch adds a new ioctl
> command, given a perf event fd, to query the bpf program array
> attached to the same perf tracepoint event.
>
> The new uapi ioctl command:
> PERF_EVENT_IOC_QUERY_BPF
>
> The new uapi/linux/perf_event.h structure:
> struct perf_event_query_bpf {
> __u64 prog_ids;
> __u32 prog_cnt;
> };
>
> The usage:
> struct perf_event_query_bpf query;
> query.prog_ids = (__u64)usr_prog_ids_buf;
> query.prog_cnt = usr_prog_ids_buf_len;
> err = ioctl(pmu_efd, PERF_EVENT_IOC_QUERY_BPF, &query);
>
> Signed-off-by: Yonghong Song <y...@fb.com>
> Acked-by: Alexei Starovoitov <a...@kernel.org>
Can you please fix that example to make it clear that prog_ids is in
fact a pointer to an array of size prog_cnt. Ideally also describing
what the type of array is.
In fact, would not something like:
struct perf_event_query_bpf {
__u32 len;
__u32 __reserved;
__u64 ids[0];
};
be a much clearer interface?
Also, you forgot to tell us why we need this interface at all.
