efi: Return grub_efi_status_t from grub_efi_get_variable()

This is needed to properly detect and report UEFI Secure Boot status
to the x86 Linux kernel. The functionality will be added by subsequent
patches.

Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Signed-off-by: Marco A Benatto <mbenatto@redhat.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/kern/efi/efi.c

@@ -223,9 +223,9 @@ grub_efi_set_variable(const char *var, const grub_efi_guid_t *guid,
   return grub_error (GRUB_ERR_IO, "could not set EFI variable `%s'", var);
 }
 
-void *
+grub_efi_status_t
 grub_efi_get_variable (const char *var, const grub_efi_guid_t *guid,
-		       grub_size_t *datasize_out)
+		       grub_size_t *datasize_out, void **data_out)
 {
   grub_efi_status_t status;
   grub_efi_uintn_t datasize = 0;
@@ -234,13 +234,14 @@ grub_efi_get_variable (const char *var, const grub_efi_guid_t *guid,
   void *data;
   grub_size_t len, len16;
 
+  *data_out = NULL;
   *datasize_out = 0;
 
   len = grub_strlen (var);
   len16 = len * GRUB_MAX_UTF16_PER_UTF8;
   var16 = grub_calloc (len16 + 1, sizeof (var16[0]));
   if (!var16)
-    return NULL;
+    return GRUB_EFI_OUT_OF_RESOURCES;
   len16 = grub_utf8_to_utf16 (var16, len16, (grub_uint8_t *) var, len, NULL);
   var16[len16] = 0;
 
@@ -251,14 +252,14 @@ grub_efi_get_variable (const char *var, const grub_efi_guid_t *guid,
   if (status != GRUB_EFI_BUFFER_TOO_SMALL || !datasize)
     {
       grub_free (var16);
-      return NULL;
+      return status;
     }
 
   data = grub_malloc (datasize);
   if (!data)
     {
       grub_free (var16);
-      return NULL;
+      return GRUB_EFI_OUT_OF_RESOURCES;
     }
 
   status = efi_call_5 (r->get_variable, var16, guid, NULL, &datasize, data);
@@ -266,12 +267,13 @@ grub_efi_get_variable (const char *var, const grub_efi_guid_t *guid,
 
   if (status == GRUB_EFI_SUCCESS)
     {
+      *data_out = data;
       *datasize_out = datasize;
-      return data;
+      return status;
     }
 
   grub_free (data);
-  return NULL;
+  return status;
 }
 
 #pragma GCC diagnostic ignored "-Wcast-align"