netdev - [PATCH bpf-next v2 2/8] libbpf: Add a helper for retrieving a prog via index

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Date:   Mon, 21 Jan 2019 10:10:35 +0100
From:   Maciej Fijalkowski <maciejromanfijalkowski@...il.com>
To:     daniel@...earbox.net, ast@...nel.org
Cc:     netdev@...r.kernel.org, jakub.kicinski@...ronome.com,
        brouer@...hat.com
Subject: [PATCH bpf-next v2 2/8] libbpf: Add a helper for retrieving a prog via index

xdp_redirect_cpu has a 6 different XDP programs that can be attached to
network interface. This sample has a option --prognum that allows user
for specifying which particular program from a given set will be
attached to network interface.
In order to make it easier when converting the mentioned sample to
libbpf usage, add a function to libbpf that will return program's fd for
a given index.

Note that there is already a bpf_object__find_prog_by_idx, which could
be exported and might be used for that purpose, but it operates on the
number of ELF section and here we need an index from a programs array
within the bpf_object.

Signed-off-by: Maciej Fijalkowski <maciejromanfijalkowski@...il.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
---
 tools/lib/bpf/libbpf.c   | 8 ++++++++
 tools/lib/bpf/libbpf.h   | 3 +++
 tools/lib/bpf/libbpf.map | 1 +
 3 files changed, 12 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index dc838bea403f..21c84d0f6128 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -935,6 +935,14 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
 	return err;
 }
 
+int
+bpf_object__get_prog_fd_by_num(struct bpf_object *obj, int idx)
+{
+	if (idx >= 0 && idx < obj->nr_programs)
+		return bpf_program__fd(&obj->programs[idx]);
+	return -ENOENT;
+}
+
 static struct bpf_program *
 bpf_object__find_prog_by_idx(struct bpf_object *obj, int idx)
 {
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 7f10d36abdde..ca1b381cb3ad 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -95,6 +95,9 @@ LIBBPF_API int bpf_object__btf_fd(const struct bpf_object *obj);
 LIBBPF_API struct bpf_program *
 bpf_object__find_program_by_title(struct bpf_object *obj, const char *title);
 
+LIBBPF_API int
+bpf_object__get_prog_fd_by_num(struct bpf_object *obj, int idx);
+
 LIBBPF_API struct bpf_object *bpf_object__next(struct bpf_object *prev);
 #define bpf_object__for_each_safe(pos, tmp)			\
 	for ((pos) = bpf_object__next(NULL),		\
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 7c59e4f64082..871d2fc07150 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -127,4 +127,5 @@ LIBBPF_0.0.1 {
 LIBBPF_0.0.2 {
 	global:
 		bpf_object__find_map_fd_by_name;
+		bpf_object__get_prog_fd_by_num;
 } LIBBPF_0.0.1;
-- 
2.16.1