[PATCH v2 bpf-next 5/6] libbpf: Introduce bpf_prog_attach_xattr

[Andrey Ignatov <rdna@fb.com>]

Introduce a new bpf_prog_attach_xattr function that accepts an
extendable struct bpf_prog_attach_opts and supports passing a new
attribute to BPF_PROG_ATTACH command: replace_prog_fd that is fd of
previously attached cgroup-bpf program to replace if recently introduced
BPF_F_REPLACE flag is used.

The new function is named to be consistent with other xattr-functions
(bpf_prog_test_run_xattr, bpf_create_map_xattr, bpf_load_program_xattr).

The struct bpf_prog_attach_opts is supposed to be used with
DECLARE_LIBBPF_OPTS framework.

The opts argument is used directly in bpf_prog_attach_xattr
implementation since at the time of adding all fields already exist in
the kernel. New fields, if added, will need to be used via OPTS_* macros
from libbpf_internal.h.

Signed-off-by: Andrey Ignatov <rdna@fb.com>
---
 tools/lib/bpf/bpf.c      | 21 +++++++++++++++++----
 tools/lib/bpf/bpf.h      | 12 ++++++++++++
 tools/lib/bpf/libbpf.map |  2 ++
 3 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 98596e15390f..9f4e42abd185 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -466,14 +466,27 @@ int bpf_obj_get(const char *pathname)
 
 int bpf_prog_attach(int prog_fd, int target_fd, enum bpf_attach_type type,
 		    unsigned int flags)
+{
+	DECLARE_LIBBPF_OPTS(bpf_prog_attach_opts, opts,
+		.target_fd = target_fd,
+		.prog_fd = prog_fd,
+		.type = type,
+		.flags = flags,
+	);
+
+	return bpf_prog_attach_xattr(&opts);
+}
+
+int bpf_prog_attach_xattr(const struct bpf_prog_attach_opts *opts)
 {
 	union bpf_attr attr;
 
 	memset(&attr, 0, sizeof(attr));
-	attr.target_fd	   = target_fd;
-	attr.attach_bpf_fd = prog_fd;
-	attr.attach_type   = type;
-	attr.attach_flags  = flags;
+	attr.target_fd	   = opts->target_fd;
+	attr.attach_bpf_fd = opts->prog_fd;
+	attr.attach_type   = opts->type;
+	attr.attach_flags  = opts->flags;
+	attr.replace_bpf_fd = opts->replace_prog_fd;
 
 	return sys_bpf(BPF_PROG_ATTACH, &attr, sizeof(attr));
 }
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 5cfe6e0a1aef..5b5f9b374074 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -150,8 +150,20 @@ LIBBPF_API int bpf_map_get_next_key(int fd, const void *key, void *next_key);
 LIBBPF_API int bpf_map_freeze(int fd);
 LIBBPF_API int bpf_obj_pin(int fd, const char *pathname);
 LIBBPF_API int bpf_obj_get(const char *pathname);
+
+struct bpf_prog_attach_opts {
+	size_t sz; /* size of this struct for forward/backward compatibility */
+	int target_fd;
+	int prog_fd;
+	enum bpf_attach_type type;
+	unsigned int flags;
+	int replace_prog_fd;
+};
+#define bpf_prog_attach_opts__last_field replace_prog_fd
+
 LIBBPF_API int bpf_prog_attach(int prog_fd, int attachable_fd,
 			       enum bpf_attach_type type, unsigned int flags);
+LIBBPF_API int bpf_prog_attach_xattr(const struct bpf_prog_attach_opts *opts);
 LIBBPF_API int bpf_prog_detach(int attachable_fd, enum bpf_attach_type type);
 LIBBPF_API int bpf_prog_detach2(int prog_fd, int attachable_fd,
 				enum bpf_attach_type type);
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 495df575f87f..42b065454031 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -210,4 +210,6 @@ LIBBPF_0.0.6 {
 } LIBBPF_0.0.5;
 
 LIBBPF_0.0.7 {
+	global:
+		bpf_prog_attach_xattr;
 } LIBBPF_0.0.6;
-- 
2.17.1