linux-kernel - [PATCH 2/6] libbpf: Define bpf_get_fd_opts and introduce bpf_map_get_fd_by_id

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Message-Id: <20221004114839.2302206-3-roberto.sassu@huaweicloud.com>
Date:   Tue,  4 Oct 2022 13:48:35 +0200
From:   Roberto Sassu <roberto.sassu@...weicloud.com>
To:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        martin.lau@...ux.dev, song@...nel.org, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
        haoluo@...gle.com, jolsa@...nel.org, mykolal@...com,
        shuah@...nel.org
Cc:     bpf@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Roberto Sassu <roberto.sassu@...wei.com>
Subject: [PATCH 2/6] libbpf: Define bpf_get_fd_opts and introduce bpf_map_get_fd_by_id_opts()

From: Roberto Sassu <roberto.sassu@...wei.com>

Define a new data structure called bpf_get_fd_opts, with the member
open_flags, to be used by callers of the _opts variants of
bpf_*_get_fd_by_id() to specify the permissions needed for the file
descriptor to be obtained.

Also, introduce bpf_map_get_fd_by_id_opts(), to let the caller pass a
bpf_get_fd_opts structure.

Finally, keep the existing bpf_map_get_fd_by_id(), and call
bpf_map_get_fd_by_id_opts() with NULL as opts argument, to request
read-write permissions (current behavior).

Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
---
 tools/lib/bpf/bpf.c      | 12 +++++++++++-
 tools/lib/bpf/bpf.h      | 10 ++++++++++
 tools/lib/bpf/libbpf.map |  1 +
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 1d49a0352836..4b03063edf1d 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -948,19 +948,29 @@ int bpf_prog_get_fd_by_id(__u32 id)
 	return libbpf_err_errno(fd);
 }
 
-int bpf_map_get_fd_by_id(__u32 id)
+int bpf_map_get_fd_by_id_opts(__u32 id,
+			      const struct bpf_get_fd_opts *opts)
 {
 	const size_t attr_sz = offsetofend(union bpf_attr, open_flags);
 	union bpf_attr attr;
 	int fd;
 
+	if (!OPTS_VALID(opts, bpf_get_fd_opts))
+		return libbpf_err(-EINVAL);
+
 	memset(&attr, 0, attr_sz);
 	attr.map_id = id;
+	attr.open_flags = OPTS_GET(opts, open_flags, 0);
 
 	fd = sys_bpf_fd(BPF_MAP_GET_FD_BY_ID, &attr, attr_sz);
 	return libbpf_err_errno(fd);
 }
 
+int bpf_map_get_fd_by_id(__u32 id)
+{
+	return bpf_map_get_fd_by_id_opts(id, NULL);
+}
+
 int bpf_btf_get_fd_by_id(__u32 id)
 {
 	const size_t attr_sz = offsetofend(union bpf_attr, open_flags);
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 9c50beabdd14..c60eda3c88ad 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -365,7 +365,17 @@ LIBBPF_API int bpf_prog_get_next_id(__u32 start_id, __u32 *next_id);
 LIBBPF_API int bpf_map_get_next_id(__u32 start_id, __u32 *next_id);
 LIBBPF_API int bpf_btf_get_next_id(__u32 start_id, __u32 *next_id);
 LIBBPF_API int bpf_link_get_next_id(__u32 start_id, __u32 *next_id);
+
+struct bpf_get_fd_opts {
+	size_t sz; /* size of this struct for forward/backward compatibility */
+	__u32 open_flags; /* permissions requested for the operation on fd */
+	size_t :0;
+};
+#define bpf_get_fd_opts__last_field open_flags
+
 LIBBPF_API int bpf_prog_get_fd_by_id(__u32 id);
+LIBBPF_API int bpf_map_get_fd_by_id_opts(__u32 id,
+					 const struct bpf_get_fd_opts *opts);
 LIBBPF_API int bpf_map_get_fd_by_id(__u32 id);
 LIBBPF_API int bpf_btf_get_fd_by_id(__u32 id);
 LIBBPF_API int bpf_link_get_fd_by_id(__u32 id);
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 04fab9f1fdd7..2e665b21d84f 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -371,6 +371,7 @@ LIBBPF_1.0.0 {
 
 LIBBPF_1.1.0 {
 	global:
+		bpf_map_get_fd_by_id_opts;
 		user_ring_buffer__discard;
 		user_ring_buffer__free;
 		user_ring_buffer__new;
-- 
2.25.1