Add efi_delenv

Add an interface to remove / delete UEFI variables.

stand/efi/include/efilib.h

@@ -122,6 +122,7 @@ void cpy16to8(const CHAR16 *, char *, size_t);
  * the loader setting / getting FreeBSD specific variables.
  */
 
+EFI_STATUS efi_delenv(EFI_GUID *guid, const char *varname);
 EFI_STATUS efi_freebsd_getenv(const char *v, void *data, __size_t *len);
 EFI_STATUS efi_getenv(EFI_GUID *g, const char *v, void *data, __size_t *len);
 EFI_STATUS efi_global_getenv(const char *v, void *data, __size_t *len);

stand/efi/libefi/efienv.c

@@ -103,3 +103,21 @@ efi_setenv_freebsd_wcs(const char *varname, CHAR16 *valstr)
 	return (rv);
 }
 
+/*
+ * efi_delenv -- deletes the specified env variable
+ */
+EFI_STATUS
+efi_delenv(EFI_GUID *guid, const char *name)
+{
+	CHAR16 *var;
+	size_t len;
+	EFI_STATUS rv;
+
+	var = NULL;
+	if (utf8_to_ucs2(name, &var, &len) != 0)
+		return (EFI_OUT_OF_RESOURCES);
+
+	rv = RS->SetVariable(var, guid, 0, 0, NULL);
+	free(var);
+	return rv;
+}