[RFC PATCH 1/3] efi_loader: Introduce helper functions for EFI

[Ilias Apalodimas]

A following patch introduces a different logic for loading initrd's
based on the EFI_LOAD_FILE2_PROTOCOL.
Since similar logic can be applied in the future for other system files
(i.e DTBs), let's add some helper functions which will retrieve and
parse file paths stored in EFI load options.

Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
---
 include/efi_helper.h        |  23 ++++++
 lib/efi_loader/efi_helper.c | 146 ++++++++++++++++++++++++++++++++++++
 2 files changed, 169 insertions(+)
 create mode 100644 include/efi_helper.h
 create mode 100644 lib/efi_loader/efi_helper.c

diff --git a/include/efi_helper.h b/include/efi_helper.h
new file mode 100644
index 000000000000..4e6bd2f036df
--- /dev/null
+++ b/include/efi_helper.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (c) 2020, Linaro Limited
+ */
+
+#if !defined _EFI_HELPER_H_
+#define _EFI_HELPER_H
+
+#include <efi.h>
+#include <efi_api.h>
+
+enum load_option_dp_type {
+	BOOT_IMAGE_DP,
+	INITRD_DP,
+	DTB_DP,
+};
+
+void *efi_get_var(u16 *name, const efi_guid_t *vendor, efi_uintn_t *size);
+struct efi_device_path *efi_get_fp_from_boot(int idx);
+struct efi_device_path *efi_dp_instance_by_idx(struct efi_device_path *dp,
+					       efi_uintn_t *size, int idx);
+
+#endif
diff --git a/lib/efi_loader/efi_helper.c b/lib/efi_loader/efi_helper.c
new file mode 100644
index 000000000000..e2437a4f698b
--- /dev/null
+++ b/lib/efi_loader/efi_helper.c
@@ -0,0 +1,146 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) 2020, Linaro Limited
+ */
+
+#include <common.h>
+#include <env.h>
+#include <malloc.h>
+#include <dm.h>
+#include <fs.h>
+#include <efi_helper.h>
+#include <efi_loader.h>
+#include <efi_variable.h>
+
+/**
+ * efi_get_var() - read value of an EFI variable
+ *
+ * @name:	variable name
+ * @start:	vendor GUID
+ * @size:	size of allocated buffer
+ *
+ * Return:	buffer with variable data or NULL
+ */
+void *efi_get_var(u16 *name, const efi_guid_t *vendor, efi_uintn_t *size)
+{
+	efi_status_t ret;
+	void *buf = NULL;
+
+	*size = 0;
+	ret = efi_get_variable_int(name, vendor, NULL, size, buf, NULL);
+	if (ret == EFI_BUFFER_TOO_SMALL) {
+		buf = malloc(*size);
+		ret = efi_get_variable_int(name, vendor, NULL, size, buf, NULL);
+	}
+
+	if (ret != EFI_SUCCESS) {
+		free(buf);
+		*size = 0;
+		return NULL;
+	}
+
+	return buf;
+}
+
+/**
+ * efi_dp_instance_by_idx() - Get a file path with a specific index
+ *
+ * @name:	device path array
+ * @size:	size of the discovered device path
+ * @idx:	index of the device path
+ *
+ * Return:	device path or NULL. Caller must free the returned value
+ */
+
+struct
+efi_device_path *efi_dp_instance_by_idx(struct efi_device_path *dp,
+					efi_uintn_t *size, int idx)
+{
+	struct efi_device_path *instance = NULL;
+	efi_uintn_t instance_size = 0;
+
+	if (!efi_dp_is_multi_instance(dp))
+		return NULL;
+
+	while (idx >= 0 && dp) {
+		instance = efi_dp_get_next_instance(&dp, &instance_size);
+		if (idx && instance) {
+			efi_free_pool(instance);
+			instance_size = 0;
+			instance = NULL;
+		}
+		idx--;
+	}
+	*size = instance_size;
+
+	return instance;
+}
+
+/**
+ * create_boot_var_indexed() - Return Boot#### name were #### is replaced by
+ *			       the value of BootCurrent
+ *
+ * @var_name:		variable name
+ * @var_name_size:	size of var_name
+ *
+ * Return:	Status code
+ */
+static efi_status_t create_boot_var_indexed(u16 var_name[], size_t var_name_size)
+{
+	efi_uintn_t boot_order_size;
+	efi_status_t ret;
+	u16 boot_order;
+	u16 *pos;
+
+	boot_order_size = sizeof(boot_order);
+	ret = efi_get_variable_int(L"BootCurrent",
+				   &efi_global_variable_guid, NULL,
+				   &boot_order_size, &boot_order, NULL);
+	if (ret != EFI_SUCCESS)
+		goto out;
+
+	pos = efi_create_indexed_name(var_name, var_name_size, "Boot",
+				      boot_order);
+	if (!pos) {
+		ret = EFI_OUT_OF_RESOURCES;
+		goto out;
+	}
+
+out:
+	return ret;
+}
+
+/**
+ * efi_get_fp_from_var() - Retrieve and return a device path from an EFI
+ *			   Boot### variable
+ *
+ * @idx:	index of the instance to retrieve
+ *
+ * Return:	device path of NULL. Caller must free the returned value
+ */
+struct efi_device_path *efi_get_fp_from_boot(int idx)
+{
+	struct efi_device_path *file_path;
+	struct efi_load_option lo;
+	void *var_value = NULL;
+	efi_uintn_t size;
+	efi_status_t ret;
+	u16 var_name[16];
+
+	ret = create_boot_var_indexed(var_name, sizeof(var_name));
+	if (ret != EFI_SUCCESS)
+		return NULL;
+
+	var_value = efi_get_var(var_name, &efi_global_variable_guid, &size);
+	if (!var_value)
+		return NULL;
+
+	efi_deserialize_load_option(&lo, var_value, &size);
+	file_path = efi_dp_instance_by_idx(lo.file_path, &size, idx);
+	if (!file_path) {
+		printf("Instance not found\n");
+		return NULL;
+	}
+
+	return file_path;
+}
-- 
2.30.0.rc2