libkmod: Add build-id item to kmod_module_get_info()

If available, add the build-id to the info list returned by
kmod_module_get_info(). This allows us to compare the build-id of a
loaded module versus the build-id of the file. It's rather cumbersome
command, but it works:

	$ ./build/modinfo -F build-id hid
	AE:7A:2E:37:E0:2B:31:D5:72:7C:87:87:15:8C:05:FA:77:7A:4F:57
	$ xxd -p -u -s16  /sys/module/hid/notes/.note.gnu.build-id  | sed 's/../&:/g;s/:$//'
	AE:7A:2E:37:E0:2B:31:D5:72:7C:87:87:15:8C:05:FA:77:7A:4F:57

An option to modinfo to really to just dump the raw value can be added
in future.

Signed-off-by: Lucas De Marchi <demarchi@kernel.org>

Author: lucasdemarchi

libkmod/libkmod-module.c

@@ -1853,7 +1853,7 @@ static struct kmod_list *kmod_module_info_append_hex(struct kmod_list **list,
 KMOD_EXPORT int kmod_module_get_info(const struct kmod_module *mod,
 				     struct kmod_list **list)
 {
-	struct kmod_elf *elf;
+	struct kmod_elf *elf = NULL;
 	char **strings;
 	int i, count, ret = -ENOMEM;
 	struct kmod_signature_info sig_info = {};
@@ -1901,6 +1901,22 @@ KMOD_EXPORT int kmod_module_get_info(const struct kmod_module *mod,
 			goto list_error;
 	}
 
+	if (elf != NULL) {
+		const void *build_id;
+		size_t build_id_len;
+
+		if (kmod_elf_get_build_id(elf, &build_id, &build_id_len) == 0) {
+			struct kmod_list *n;
+
+			n = kmod_module_info_append_hex(list, "build-id",
+							strlen("build-id"), build_id,
+							build_id_len);
+			if (n == NULL)
+				goto list_error;
+			count++;
+		}
+	}
+
 	if (mod->file && kmod_module_signature_info(mod->file, &sig_info)) {
 		struct kmod_list *n;