bpf: Change btf_iter func proto prefix to "bpf_iter_"

This is to be consistent with tracing and lsm programs
which have prefix "bpf_trace_" and "bpf_lsm_" respectively.
Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200513180216.2949387-1-yhs@fb.com

include/linux/bpf.h

@@ -1131,10 +1131,10 @@ struct bpf_link *bpf_link_get_from_fd(u32 ufd);
 int bpf_obj_pin_user(u32 ufd, const char __user *pathname);
 int bpf_obj_get_user(const char __user *pathname, int flags);
 
-#define BPF_ITER_FUNC_PREFIX "__bpf_iter__"
+#define BPF_ITER_FUNC_PREFIX "bpf_iter_"
 #define DEFINE_BPF_ITER_FUNC(target, args...)			\
-	extern int __bpf_iter__ ## target(args);		\
-	int __init __bpf_iter__ ## target(args) { return 0; }
+	extern int bpf_iter_ ## target(args);			\
+	int __init bpf_iter_ ## target(args) { return 0; }
 
 typedef int (*bpf_iter_init_seq_priv_t)(void *private_data);
 typedef void (*bpf_iter_fini_seq_priv_t)(void *private_data);

tools/lib/bpf/libbpf.c

@@ -6919,7 +6919,7 @@ static int bpf_object__collect_st_ops_relos(struct bpf_object *obj,
 
 #define BTF_TRACE_PREFIX "btf_trace_"
 #define BTF_LSM_PREFIX "bpf_lsm_"
-#define BTF_ITER_PREFIX "__bpf_iter__"
+#define BTF_ITER_PREFIX "bpf_iter_"
 #define BTF_MAX_NAME_SIZE 128
 
 static int find_btf_by_prefix_kind(const struct btf *btf, const char *prefix,