tools lib bpf: Add flags to bpf_create_map()

Commit 6c905981743 ("bpf: pre-allocate hash map elements") introduces
map_flags to bpf_attr for BPF_MAP_CREATE command. Expose this new
parameter in libbpf.

By exposing it, users can access flags such as whether or not to
preallocate the map.

Signed-off-by: Joe Stringer <joe@ovn.org>
Acked-by: Wang Nan <wangnan0@huawei.com>
Cc: Alexei Starovoitov <ast@fb.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Link: http://lkml.kernel.org/r/20161209024620.31660-4-joe@ovn.org
[ Added clarifying comment made by Wang Nan ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/bpf/bpf.c

@@ -54,7 +54,7 @@ static int sys_bpf(enum bpf_cmd cmd, union bpf_attr *attr,
 }
 
 int bpf_create_map(enum bpf_map_type map_type, int key_size,
-		   int value_size, int max_entries)
+		   int value_size, int max_entries, __u32 map_flags)
 {
 	union bpf_attr attr;
 
@@ -64,6 +64,7 @@ int bpf_create_map(enum bpf_map_type map_type, int key_size,
 	attr.key_size = key_size;
 	attr.value_size = value_size;
 	attr.max_entries = max_entries;
+	attr.map_flags = map_flags;
 
 	return sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
 }

tools/lib/bpf/bpf.h

@@ -24,7 +24,7 @@
 #include <linux/bpf.h>
 
 int bpf_create_map(enum bpf_map_type map_type, int key_size, int value_size,
-		   int max_entries);
+		   int max_entries, __u32 map_flags);
 
 /* Recommend log buffer size */
 #define BPF_LOG_BUF_SIZE 65536

tools/lib/bpf/libbpf.c

@@ -854,7 +854,8 @@ bpf_object__create_maps(struct bpf_object *obj)
 		*pfd = bpf_create_map(def->type,
 				      def->key_size,
 				      def->value_size,
-				      def->max_entries);
+				      def->max_entries,
+				      0);
 		if (*pfd < 0) {
 			size_t j;
 			int err = *pfd;