Support --with-env-file-name

Allow configuration to override the default ENV_FILE_NAME
and FAT_ENV_FILENAME to support scenarios with multiple
distributions or architectures.

For multiple distributions, https://wiki.debian.org/UEFI explains:

> Debian installs grub-efi for its EFI bootloader, as:
>
> Architecture Path
> amd64        \EFI\debian\grubx64.efi
> i386         \EFI\debian\grubia32.efi
> arm64        \EFI\debian\grubaa64.efi
> armhf        \EFI\debian\grubarm.efi

Other distributions use their own directories (eg \EFI\fedora, etc).

EFI Boot Guard (EBG) looks for a specific data file (normally BGENV.DAT)
which contains a single kernel configuration entry. Using the new
--with-env-file-name option, each distribution builds and configures
its own instance of EBG, which can find its corresponding
data file (eg BGENV-DEBIAN.DAT, or EFI\debian\BGENV.DAT, etc). This
also has the benefit of decoupling the distributions at boot so that
a breaking EBG change to one distribution will not affect another.

Signed-off-by: Earl Chew <earl_chew@yahoo.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

configure.ac

@@ -153,6 +153,19 @@ AC_ARG_WITH([env-backend],
 
 AC_SUBST([env_api_file], [${ENV_API_FILE}])
 
+AC_ARG_WITH([env-file-name],
+	    AS_HELP_STRING([--with-env-file-name=STRING],
+                           [override the boot environment file name]),
+	    [
+		ENV_FILE_NAME="$withval"
+	    ],
+	    [ ENV_FILE_NAME="BGENV.DAT" ])
+
+AC_DEFINE_UNQUOTED(
+	[ENV_FILE_NAME], [L"${ENV_FILE_NAME}"], [Boot environment file name])
+AC_DEFINE_UNQUOTED(
+	[FAT_ENV_FILENAME], ["${ENV_FILE_NAME}"], [Boot environment FAT file name])
+
 AC_ARG_WITH([boot-delay],
 	    AS_HELP_STRING([--with-boot-delay=INT],
 			   [specify the additional boot delay in seconds, defaults to 3]),
@@ -295,6 +308,7 @@ AC_MSG_RESULT([
 	efi libs:                ${GNUEFI_LIB_DIR}
 
 	environment backend:     ${ENV_API_FILE}.c
+	environment file name:   ${ENV_FILE_NAME}
 	number of config parts:  ${ENV_NUM_CONFIG_PARTS}
 	reserved for uservars:   ${ENV_MEM_USERVARS} bytes
 	silent boot:             ${silent_boot}

include/envdata.h

@@ -16,8 +16,6 @@
 
 #include <stdint.h>
 
-#define ENV_FILE_NAME L"BGENV.DAT"
-#define FAT_ENV_FILENAME "BGENV.DAT"
 #define ENV_STRING_LENGTH 255
 
 #define USTATE_OK 0