[PATCH bpf-next v4 5/6] libbpf: Add log_opts support for bpf_link_create

[Leon Hwang <leon.hwang@linux.dev>]

Since the iter_info and iter_info_len in struct bpf_link_create_opts are
legacy, reuse the slot of iter_info to place log_opts.

When adding log_opts support for iter link_create in the future, we will
move the iter_info and iter_info_len to the last union, see below. And,
keep the backward compatibility meanwhile, that uses iter_info if
iter_info_len is set.

struct bpf_link_create_opts {
	/* ... */
	union {
		/* ... */
		strut {
			struct bpf_iter_link_info *info;
			__u32 len;
		} iter;
	};
};

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 tools/lib/bpf/bpf.c | 20 +++++++++++++++++---
 tools/lib/bpf/bpf.h |  5 ++++-
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 9a2107d4f6d8..00efa90a6ed9 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -794,6 +794,8 @@ int bpf_link_create(int prog_fd, int target_fd,
 {
 	const size_t attr_sz = offsetofend(union bpf_attr, link_create);
 	__u32 target_btf_id, iter_info_len, relative_id;
+	union bpf_iter_link_info *iter_info = NULL;
+	struct bpf_log_opts *log_opts = NULL;
 	int fd, err, relative_fd;
 	union bpf_attr attr;
 
@@ -803,6 +805,14 @@ int bpf_link_create(int prog_fd, int target_fd,
 	iter_info_len = OPTS_GET(opts, iter_info_len, 0);
 	target_btf_id = OPTS_GET(opts, target_btf_id, 0);
 
+	if (iter_info_len && attach_type != BPF_TRACE_ITER)
+		return libbpf_err(-EINVAL);
+
+	if (iter_info_len)
+		iter_info = OPTS_GET(opts, iter_info, (void *)0);
+	else
+		log_opts = OPTS_GET(opts, log_opts, (void *)0);
+
 	/* validate we don't have unexpected combinations of non-zero fields */
 	if (iter_info_len || target_btf_id) {
 		if (iter_info_len && target_btf_id)
@@ -824,7 +834,7 @@ int bpf_link_create(int prog_fd, int target_fd,
 
 	switch (attach_type) {
 	case BPF_TRACE_ITER:
-		attr.link_create.iter_info = ptr_to_u64(OPTS_GET(opts, iter_info, (void *)0));
+		attr.link_create.iter_info = ptr_to_u64(iter_info);
 		attr.link_create.iter_info_len = iter_info_len;
 		break;
 	case BPF_PERF_EVENT:
@@ -960,12 +970,12 @@ int bpf_link_create(int prog_fd, int target_fd,
 			return libbpf_err(-EINVAL);
 		break;
 	default:
-		if (!OPTS_ZEROED(opts, flags))
+		if (!OPTS_ZEROED(opts, iter_info_len))
 			return libbpf_err(-EINVAL);
 		break;
 	}
 proceed:
-	fd = sys_bpf_fd(BPF_LINK_CREATE, &attr, attr_sz);
+	fd = __sys_bpf_fd(&attr, attr_sz, BPF_LINK_CREATE, log_opts);
 	if (fd >= 0)
 		return fd;
 	/* we'll get EINVAL if LINK_CREATE doesn't support attaching fentry
@@ -975,6 +985,10 @@ int bpf_link_create(int prog_fd, int target_fd,
 	if (err != -EINVAL)
 		return libbpf_err(err);
 
+	/* bpf_raw_tracepoint_open() does not support log_opts */
+	if (log_opts)
+		return libbpf_err(err);
+
 	/* if user used features not supported by
 	 * BPF_RAW_TRACEPOINT_OPEN command, then just give up immediately
 	 */
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 826d9cc9ab65..fe3b7fd8512b 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -422,7 +422,10 @@ union bpf_iter_link_info; /* defined in up-to-date linux/bpf.h */
 struct bpf_link_create_opts {
 	size_t sz; /* size of this struct for forward/backward compatibility */
 	__u32 flags;
-	union bpf_iter_link_info *iter_info;
+	union {
+		union bpf_iter_link_info *iter_info;
+		struct bpf_log_opts *log_opts;
+	};
 	__u32 iter_info_len;
 	__u32 target_btf_id;
 	union {
-- 
2.55.0