efi_loader: Add helper functions for EFI

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@linaro.org>

1 files changed, 33 insertions, 0 deletions

diff --git a/lib/efi_loader/efi_var_common.c b/lib/efi_loader/efi_var_common.c
index 1c7459266a..b11ed91a74 100644
--- a/lib/efi_loader/efi_var_common.c
+++ b/lib/efi_loader/efi_var_common.c
@@ -9,6 +9,7 @@
 #include <common.h>
 #include <efi_loader.h>
 #include <efi_variable.h>
+#include <stdlib.h>
 
 enum efi_secure_mode {
 	EFI_MODE_SETUP,
@@ -343,3 +344,35 @@ enum efi_auth_var_type efi_auth_var_get_type(u16 *name, const efi_guid_t *guid)
 	}
 	return EFI_AUTH_VAR_NONE;
 }
+
+/**
+ * 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;
+}