[PATCH 3/6] 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 variables.

Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
---
 include/efi_helper.h        |  15 +++++
 lib/efi_loader/Makefile     |   1 +
 lib/efi_loader/efi_helper.c | 118 ++++++++++++++++++++++++++++++++++++
 3 files changed, 134 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..4980a1bb35d7
--- /dev/null
+++ b/include/efi_helper.h
@@ -0,0 +1,15 @@
+/* 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>
+
+void *efi_get_var(u16 *name, const efi_guid_t *vendor, efi_uintn_t *size);
+struct efi_device_path *efi_get_dp_from_boot(const efi_guid_t guid);
+
+#endif
diff --git a/lib/efi_loader/Makefile b/lib/efi_loader/Makefile
index 10b42e8847bf..da2741adecfa 100644
--- a/lib/efi_loader/Makefile
+++ b/lib/efi_loader/Makefile
@@ -23,6 +23,7 @@ endif
 obj-$(CONFIG_CMD_BOOTEFI_HELLO) += helloworld_efi.o
 obj-$(CONFIG_CMD_BOOTEFI_BOOTMGR) += efi_bootmgr.o
 obj-y += efi_boottime.o
+obj-y += efi_helper.o
 obj-$(CONFIG_EFI_HAVE_CAPSULE_SUPPORT) += efi_capsule.o
 obj-$(CONFIG_EFI_CAPSULE_FIRMWARE) += efi_firmware.o
 obj-y += efi_console.o
diff --git a/lib/efi_loader/efi_helper.c b/lib/efi_loader/efi_helper.c
new file mode 100644
index 000000000000..5437faa3ec49
--- /dev/null
+++ b/lib/efi_loader/efi_helper.c
@@ -0,0 +1,118 @@
+// 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_load_initrd.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);
+		if (!buf)
+			return NULL;
+		ret = efi_get_variable_int(name, vendor, NULL, size, buf, NULL);
+	}
+
+	if (ret != EFI_SUCCESS) {
+		free(buf);
+		*size = 0;
+		return NULL;
+	}
+
+	return buf;
+}
+
+/**
+ * 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_current_size;
+	efi_status_t ret;
+	u16 boot_current;
+	u16 *pos;
+
+	boot_current_size = sizeof(boot_current);
+	ret = efi_get_variable_int(L"BootCurrent",
+				   &efi_global_variable_guid, NULL,
+				   &boot_current_size, &boot_current, NULL);
+	if (ret != EFI_SUCCESS)
+		goto out;
+
+	pos = efi_create_indexed_name(var_name, var_name_size, "Boot",
+				      boot_current);
+	if (!pos) {
+		ret = EFI_OUT_OF_RESOURCES;
+		goto out;
+	}
+
+out:
+	return ret;
+}
+
+/**
+ * efi_get_dp_from_boot() - Retrieve and return a device path from an EFI
+ *			    Boot### variable
+ *
+ * @guid:	Vendor guid of the VenMedia DP
+ *
+ * Return:	device path or NULL. Caller must free the returned value
+ */
+struct efi_device_path *efi_get_dp_from_boot(const efi_guid_t guid)
+{
+	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;
+
+	ret = efi_deserialize_load_option(&lo, var_value, &size);
+	if (ret != EFI_SUCCESS)
+		return NULL;
+
+	file_path = efi_dp_from_lo(&lo, &size, guid);
+	if (!file_path) {
+		log_debug("Missing file path in %ls", var_name);
+		return NULL;
+	}
+
+	return file_path;
+}
-- 
2.30.1