Merge branch 'btf_get_next_id'

Quentin Monnet says:

====================
This set adds a new command BPF_BTF_GET_NEXT_ID to the bpf() system call,
adds the relevant API function in libbpf, and uses it in bpftool to list
all BTF objects loaded on the system (and to dump the ids of maps and
programs associated with them, if any).

The main motivation of listing BTF objects is introspection and debugging
purposes. By getting BPF program and map information, it should already be
possible to list all BTF objects associated to at least one map or one
program. But there may be unattached BTF objects, held by a file descriptor
from a user space process only, and we may want to list them too.

As a side note, it also turned useful for examining the BTF objects
attached to offloaded programs, which would not show in program information
because the BTF id is not copied when retrieving such info. A fix is in
progress on that side.

v2:
- Rebase patch with new libbpf function on top of Andrii's changes
  regarding libbpf versioning.
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

3 files changed, 15 insertions, 12 deletions

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index c7d7993c44bb..cbb933532981 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -568,7 +568,7 @@ int bpf_prog_test_run_xattr(struct bpf_prog_test_run_attr *test_attr)
 	return ret;
 }
 
-int bpf_prog_get_next_id(__u32 start_id, __u32 *next_id)
+static int bpf_obj_get_next_id(__u32 start_id, __u32 *next_id, int cmd)
 {
 	union bpf_attr attr;
 	int err;
@@ -576,26 +576,26 @@ int bpf_prog_get_next_id(__u32 start_id, __u32 *next_id)
 	memset(&attr, 0, sizeof(attr));
 	attr.start_id = start_id;
 
-	err = sys_bpf(BPF_PROG_GET_NEXT_ID, &attr, sizeof(attr));
+	err = sys_bpf(cmd, &attr, sizeof(attr));
 	if (!err)
 		*next_id = attr.next_id;
 
 	return err;
 }
 
-int bpf_map_get_next_id(__u32 start_id, __u32 *next_id)
+int bpf_prog_get_next_id(__u32 start_id, __u32 *next_id)
 {
-	union bpf_attr attr;
-	int err;
-
-	memset(&attr, 0, sizeof(attr));
-	attr.start_id = start_id;
+	return bpf_obj_get_next_id(start_id, next_id, BPF_PROG_GET_NEXT_ID);
+}
 
-	err = sys_bpf(BPF_MAP_GET_NEXT_ID, &attr, sizeof(attr));
-	if (!err)
-		*next_id = attr.next_id;
+int bpf_map_get_next_id(__u32 start_id, __u32 *next_id)
+{
+	return bpf_obj_get_next_id(start_id, next_id, BPF_MAP_GET_NEXT_ID);
+}
 
-	return err;
+int bpf_btf_get_next_id(__u32 start_id, __u32 *next_id)
+{
+	return bpf_obj_get_next_id(start_id, next_id, BPF_BTF_GET_NEXT_ID);
 }
 
 int bpf_prog_get_fd_by_id(__u32 id)
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index ff42ca043dc8..0db01334740f 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -156,6 +156,7 @@ LIBBPF_API int bpf_prog_test_run(int prog_fd, int repeat, void *data,
 				 __u32 *retval, __u32 *duration);
 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_prog_get_fd_by_id(__u32 id);
 LIBBPF_API int bpf_map_get_fd_by_id(__u32 id);
 LIBBPF_API int bpf_btf_get_fd_by_id(__u32 id);
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 4e72df8e98ba..664ce8e7a60e 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -186,4 +186,6 @@ LIBBPF_0.0.4 {
 } LIBBPF_0.0.3;
 
 LIBBPF_0.0.5 {
+	global:
+		bpf_btf_get_next_id;
 } LIBBPF_0.0.4;