tools lib bpf: Add bpf_prog_{attach,detach}

Commit d8c5b17f2bc0 ("samples: bpf: add userspace example for attaching
eBPF programs to cgroups") added these functions to samples/libbpf, but
during this merge all of the samples libbpf functionality is shifting to
tools/lib/bpf. Shift these functions there.

Committer notes:

Use bzero + attr.FIELD = value instead of 'attr = { .FIELD = value, just
like the other wrapper calls to sys_bpf with bpf_attr to make this build
in older toolchais, such as the ones in CentOS 5 and 6.

Signed-off-by: Joe Stringer <[e-mail]>
Cc: Alexei Starovoitov <[e-mail]>
Cc: Daniel Borkmann <[e-mail]>
Cc: Wang Nan <[e-mail]>
Link: http://lkml.kernel.org/n/[e-mail]
Link: https://github.com/joestringer/linux/commit/353e6f298c3d0a92fa8bfa61ff898c5050261a12.patch
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

samples/bpf/libbpf.c

···
 #include <arpa/inet.h>
 #include "libbpf.h"
 
-int bpf_prog_attach(int prog_fd, int target_fd, enum bpf_attach_type type)
-{
-	union bpf_attr attr = {
-		.target_fd = target_fd,
-		.attach_bpf_fd = prog_fd,
-		.attach_type = type,
-	};
-
-	return syscall(__NR_bpf, BPF_PROG_ATTACH, &attr, sizeof(attr));
-}
-
-int bpf_prog_detach(int target_fd, enum bpf_attach_type type)
-{
-	union bpf_attr attr = {
-		.target_fd = target_fd,
-		.attach_type = type,
-	};
-
-	return syscall(__NR_bpf, BPF_PROG_DETACH, &attr, sizeof(attr));
-}
-
 int open_raw_sock(const char *name)
 {
 	struct sockaddr_ll sll;

samples/bpf/libbpf.h

···
 
 struct bpf_insn;
 
-int bpf_prog_attach(int prog_fd, int attachable_fd, enum bpf_attach_type type);
-int bpf_prog_detach(int attachable_fd, enum bpf_attach_type type);
-
 /* ALU ops on registers, bpf_add|sub|...: dst_reg += src_reg */
 
 #define BPF_ALU64_REG(OP, DST, SRC)				\

tools/lib/bpf/bpf.c

···
 
 	return sys_bpf(BPF_OBJ_GET, &attr, sizeof(attr));
 }
+
+int bpf_prog_attach(int prog_fd, int target_fd, enum bpf_attach_type type)
+{
+	union bpf_attr attr;
+
+	bzero(&attr, sizeof(attr));
+	attr.target_fd	   = target_fd;
+	attr.attach_bpf_fd = prog_fd;
+	attr.attach_type   = type;
+
+	return sys_bpf(BPF_PROG_ATTACH, &attr, sizeof(attr));
+}
+
+int bpf_prog_detach(int target_fd, enum bpf_attach_type type)
+{
+	union bpf_attr attr;
+
+	bzero(&attr, sizeof(attr));
+	attr.target_fd	 = target_fd;
+	attr.attach_type = type;
+
+	return sys_bpf(BPF_PROG_DETACH, &attr, sizeof(attr));
+}

tools/lib/bpf/bpf.h

···
 int bpf_map_get_next_key(int fd, void *key, void *next_key);
 int bpf_obj_pin(int fd, const char *pathname);
 int bpf_obj_get(const char *pathname);
+int bpf_prog_attach(int prog_fd, int attachable_fd, enum bpf_attach_type type);
+int bpf_prog_detach(int attachable_fd, enum bpf_attach_type type);
+
 
 #endif