[PATCH v3 2/4] efi_loader: Add OS notifications for SetVariable at runtime

[Ilias Apalodimas]

Previous patches enable SetVariable at runtime using a volatile storage
backend using EFI_RUNTIME_SERVICES_DATA allocared memory. Since there's
no recommendation from the spec on how to notify the OS, add a volatile
EFI variable that contains the filename relative to the ESP. OS'es
can use that file and update it at runtime

$~ efivar -p -n b2ac5fc9-92b7-4acd-aeac-11e818c3130c-RTStorageVolatile
GUID: b2ac5fc9-92b7-4acd-aeac-11e818c3130c
Name: "RTStorageVolatile"
Attributes:
	Boot Service Access
	Runtime Service Access
Value:
00000000  75 62 6f 6f 74 65 66 69  2e 76 61 72 00           |ubootefi.var.   |

Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
---
 include/efi_loader.h         |  4 ++++
 lib/efi_loader/efi_runtime.c | 19 ++++++++++++++++---
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/include/efi_loader.h b/include/efi_loader.h
index bb51c0281774..69442f4e58de 100644
--- a/include/efi_loader.h
+++ b/include/efi_loader.h
@@ -159,6 +159,10 @@ static inline void efi_set_bootdev(const char *dev, const char *devnr,
 #define EFICONFIG_AUTO_GENERATED_ENTRY_GUID \
 	EFI_GUID(0x8108ac4e, 0x9f11, 0x4d59, \
 		 0x85, 0x0e, 0xe2, 0x1a, 0x52, 0x2c, 0x59, 0xb2)
+#define U_BOOT_EFI_RT_VAR_FILE_GUID \
+	EFI_GUID(0xb2ac5fc9, 0x92b7, 0x4acd, \
+		 0xae, 0xac, 0x11, 0xe8, 0x18, 0xc3, 0x13, 0x0c)
+
 
 /* Use internal device tree when starting UEFI application */
 #define EFI_FDT_USE_INTERNAL NULL
diff --git a/lib/efi_loader/efi_runtime.c b/lib/efi_loader/efi_runtime.c
index dde083b09665..c8f7a88ba8db 100644
--- a/lib/efi_loader/efi_runtime.c
+++ b/lib/efi_loader/efi_runtime.c
@@ -10,6 +10,7 @@
 #include <dm.h>
 #include <elf.h>
 #include <efi_loader.h>
+#include <efi_variable.h>
 #include <log.h>
 #include <malloc.h>
 #include <rtc.h>
@@ -110,6 +111,7 @@ static __efi_runtime_data efi_uintn_t efi_descriptor_size;
  */
 efi_status_t efi_init_runtime_supported(void)
 {
+	const efi_guid_t efi_guid_efi_rt_var_file = U_BOOT_EFI_RT_VAR_FILE_GUID;
 	efi_status_t ret;
 	struct efi_rt_properties_table *rt_table;
 
@@ -127,9 +129,20 @@ efi_status_t efi_init_runtime_supported(void)
 				EFI_RT_SUPPORTED_SET_VIRTUAL_ADDRESS_MAP |
 				EFI_RT_SUPPORTED_CONVERT_POINTER;
 
-	if (IS_ENABLED(CONFIG_EFI_RT_VOLATILE_STORE))
-		rt_table->runtime_services_supported |=
-			EFI_RT_SUPPORTED_SET_VARIABLE;
+	if (IS_ENABLED(CONFIG_EFI_RT_VOLATILE_STORE)) {
+		ret = efi_set_variable_int(u"RTStorageVolatile",
+					   &efi_guid_efi_rt_var_file,
+					   EFI_VARIABLE_BOOTSERVICE_ACCESS |
+					   EFI_VARIABLE_RUNTIME_ACCESS |
+					   EFI_VARIABLE_READ_ONLY,
+					   sizeof(EFI_VAR_FILE_NAME),
+					   EFI_VAR_FILE_NAME, false);
+		if (ret != EFI_SUCCESS) {
+			log_err("Failed to set RTStorageVolatile\n");
+			return ret;
+		}
+		rt_table->runtime_services_supported |= EFI_RT_SUPPORTED_SET_VARIABLE;
+	}
 
 	/*
 	 * This value must be synced with efi_runtime_detach_list
-- 
2.40.1