netdev - [PATCH bpf-next] libbpf: Add bpf_object_

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Date:   Thu, 26 Mar 2020 16:17:41 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     daniel@...earbox.net, ast@...com
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        bpf@...r.kernel.org, netdev@...r.kernel.org
Subject: [PATCH bpf-next] libbpf: Add bpf_object__rodata getter function

This adds a new getter function to libbpf to get the rodata area of a bpf
object. This is useful if a program wants to modify the rodata before
loading the object. Any such modification needs to be done before loading,
since libbpf freezes the backing map after populating it (to allow the
kernel to do dead code elimination based on its contents).

Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
---
 tools/lib/bpf/libbpf.c   | 13 +++++++++++++
 tools/lib/bpf/libbpf.h   |  1 +
 tools/lib/bpf/libbpf.map |  1 +
 3 files changed, 15 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 085e41f9b68e..d3e3bbe12f78 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1352,6 +1352,19 @@ bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
 	return 0;
 }
 
+void *bpf_object__rodata(const struct bpf_object *obj, size_t *size)
+{
+	struct bpf_map *map;
+
+	bpf_object__for_each_map(map, obj) {
+		if (map->libbpf_type == LIBBPF_MAP_RODATA && map->mmaped) {
+			*size = map->def.value_size;
+			return map->mmaped;
+		}
+	}
+	return NULL;
+}
+
 static int bpf_object__init_global_data_maps(struct bpf_object *obj)
 {
 	int err;
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index d38d7a629417..d2a9beed7b8a 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -166,6 +166,7 @@ typedef void (*bpf_object_clear_priv_t)(struct bpf_object *, void *);
 LIBBPF_API int bpf_object__set_priv(struct bpf_object *obj, void *priv,
 				    bpf_object_clear_priv_t clear_priv);
 LIBBPF_API void *bpf_object__priv(const struct bpf_object *prog);
+LIBBPF_API void *bpf_object__rodata(const struct bpf_object *obj, size_t *size);
 
 LIBBPF_API int
 libbpf_prog_type_by_name(const char *name, enum bpf_prog_type *prog_type,
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 5129283c0284..a248f4ff3a40 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -243,5 +243,6 @@ LIBBPF_0.0.8 {
 		bpf_link__pin;
 		bpf_link__pin_path;
 		bpf_link__unpin;
+		bpf_object__rodata;
 		bpf_program__set_attach_target;
 } LIBBPF_0.0.7;
-- 
2.26.0