Merge branch 'bpf-tracing-multiprog-tp-query'

Yonghong Song says:

====================
Commit e87c6bc3852b ("bpf: permit multiple bpf attachments
for a single perf event") added support to attach multiple
bpf programs to a single perf event. Given a perf event
(kprobe, uprobe, or kernel tracepoint), the perf ioctl interface
is used to query bpf programs attached to the same trace event.

There already exists a BPF_PROG_QUERY command for introspection
currently used by cgroup+bpf. We did have an implementation for
querying tracepoint+bpf through the same interface. However, it
looks cleaner to use ioctl() style of api here, since attaching
bpf prog to tracepoint/kuprobe is also done via ioctl.

Patch #1 had the core implementation and patch #2 added
a test case in tools bpf selftests suite.

Changelogs:
v3 -> v4:
  - Fix a compilation error with newer gcc like 6.3.1 while
    old gcc 4.8.5 is okay. I was using &uquery->ids to represent
    the address to the ids array to make it explicit that the
    address is passed, and this syntax is rightly rejected
    by gcc 6.3.1.
v2 -> v3:
  - Change uapi structure perf_event_query_bpf to be more
    clearer based on Peter's suggestion, and adjust
    other codes accordingly.
v1 -> v2:
  - Rebase on top of net-next.
  - Use existing bpf_prog_array_length function instead of
    implementing the same functionality in function
    bpf_prog_array_copy_info.
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 21 insertions, 0 deletions

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 86b50aa26ee8..b16c6f8f42b6 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1462,6 +1462,8 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *progs,
 	rcu_read_lock();
 	prog = rcu_dereference(progs)->progs;
 	for (; *prog; prog++) {
+		if (*prog == &dummy_bpf_prog.prog)
+			continue;
 		id = (*prog)->aux->id;
 		if (copy_to_user(prog_ids + i, &id, sizeof(id))) {
 			rcu_read_unlock();
@@ -1545,6 +1547,25 @@ int bpf_prog_array_copy(struct bpf_prog_array __rcu *old_array,
 	return 0;
 }
 
+int bpf_prog_array_copy_info(struct bpf_prog_array __rcu *array,
+			     __u32 __user *prog_ids, u32 request_cnt,
+			     __u32 __user *prog_cnt)
+{
+	u32 cnt = 0;
+
+	if (array)
+		cnt = bpf_prog_array_length(array);
+
+	if (copy_to_user(prog_cnt, &cnt, sizeof(cnt)))
+		return -EFAULT;
+
+	/* return early if user requested only program count or nothing to copy */
+	if (!request_cnt || !cnt)
+		return 0;
+
+	return bpf_prog_array_copy_to_user(array, prog_ids, request_cnt);
+}
+
 static void bpf_prog_free_deferred(struct work_struct *work)
 {
 	struct bpf_prog_aux *aux;