lib: introduce feature check in libcriu

This commit adds feature check support to libcriu. It already exists in
the CLI and RPC and this just extends it to libcriu.

This commit provides one function to do all possible feature checks in
one call. The parameter to the feature check function is a structure and
the user can enable which features should be checked.

Using a structure makes the function extensible without the need to
break the API/ABI in the future.

Signed-off-by: Adrian Reber <areber@redhat.com>

lib/c/criu.c

@@ -1925,3 +1925,75 @@ int criu_join_ns_add(const char *ns, const char *ns_file, const char *extra_opt)
 {
 	return criu_local_join_ns_add(global_opts, ns, ns_file, extra_opt);
 }
+
+int criu_local_feature_check(criu_opts *opts, struct criu_feature_check *features, size_t size)
+{
+	CriuFeatures criu_features = CRIU_FEATURES__INIT;
+	struct criu_feature_check features_copy = { 0 };
+	CriuReq req = CRIU_REQ__INIT;
+	CriuResp *resp = NULL;
+	int ret = -1;
+
+	saved_errno = 0;
+
+	if (!features)
+		goto exit;
+
+	if (size > sizeof(struct criu_feature_check))
+		goto exit;
+
+	memcpy(&features_copy, features, size);
+
+	req.type = CRIU_REQ_TYPE__FEATURE_CHECK;
+	req.opts = opts->rpc;
+
+	if (features_copy.mem_track) {
+		criu_features.has_mem_track = true;
+		criu_features.mem_track = true;
+	}
+	if (features_copy.lazy_pages) {
+		criu_features.has_lazy_pages = true;
+		criu_features.lazy_pages = true;
+	}
+	if (features_copy.pidfd_store) {
+		criu_features.has_pidfd_store = true;
+		criu_features.pidfd_store = true;
+	}
+	req.features = &criu_features;
+
+	ret = send_req_and_recv_resp(opts, &req, &resp);
+	if (ret)
+		goto exit;
+
+	memset(&features_copy, 0, sizeof(struct criu_feature_check));
+
+	if (resp->success) {
+		if (resp->features->has_mem_track) {
+			features_copy.mem_track = resp->features->mem_track;
+		}
+		if (resp->features->has_lazy_pages) {
+			features_copy.lazy_pages = resp->features->lazy_pages;
+		}
+		if (resp->features->has_pidfd_store) {
+			features_copy.pidfd_store = resp->features->pidfd_store;
+		}
+		memcpy(features, &features_copy, size);
+	} else {
+		ret = -EBADE;
+	}
+
+exit:
+	if (resp)
+		criu_resp__free_unpacked(resp, NULL);
+
+	swrk_wait(opts);
+
+	errno = saved_errno;
+
+	return ret;
+}
+
+int criu_feature_check(struct criu_feature_check *features, size_t size)
+{
+	return criu_local_feature_check(global_opts, features, size);
+}

lib/c/criu.h

@@ -288,6 +288,35 @@ int criu_local_dump_iters(criu_opts *opts, int (*more)(criu_predump_info pi));
 int criu_local_get_version(criu_opts *opts);
 int criu_local_check_version(criu_opts *opts, int minimum);
 
+/*
+ * Feature checking allows the user to check if CRIU supports
+ * certain features. There are CRIU features which do not depend
+ * on the version of CRIU but on kernel features or architecture.
+ *
+ * One example is memory tracking. Memory tracking can be disabled
+ * in the kernel or there are architectures which do not support
+ * it (aarch64 for example). By using the feature check a libcriu
+ * user can easily query CRIU if a certain feature is available.
+ *
+ * The features which should be checked can be marked in the
+ * structure 'struct criu_feature_check'. Each structure member
+ * that is set to true will result in CRIU checking for the
+ * availability of that feature in the current combination of
+ * CRIU/kernel/architecture.
+ *
+ * Available features will be set to true when the function
+ * returns successfully. Missing features will be set to false.
+ */
+
+struct criu_feature_check {
+	bool mem_track;
+	bool lazy_pages;
+	bool pidfd_store;
+};
+
+int criu_feature_check(struct criu_feature_check *features, size_t size);
+int criu_local_feature_check(criu_opts *opts, struct criu_feature_check *features, size_t size);
+
 #ifdef __GNUG__
 }
 #endif