efi_loader: bootmgr: add booting from removable media

Under the current implementation, booting from removable media using
a architecture-specific default image name, say BOOTAA64.EFI, is
supported only in distro_bootcmd script. See the commit 74522c898b35
("efi_loader: Add distro boot script for removable media").

This is, however, half-baked implementation because
1) UEFI specification requires this feature to be implemented as part
   of Boot Manager's responsibility:

  3 - Boot Manager
  3.5.1 Boot via the Simple File Protocol
  When booting via the EFI_SIMPLE_FILE_SYSTEM_PROTOCOL, the FilePath will
  start with a device path that points to the device that implements the
  EFI_SIMPLE_FILE_SYSTEM_PROTOCOL or the EFI_BLOCK_IO_PROTOCOL. The next
  part of the FilePath may point to the file name, including
  subdirectories, which contain the bootable image. If the file name is
  a null device path, the file name must be generated from the rules
  defined below.
  ...
  3.5.1.1 Removable Media Boot Behavior
  To generate a file name when none is present in the FilePath, the
  firmware must append a default file name in the form
  \EFI\BOOT\BOOT{machine type short-name}.EFI ...

2) So (1) entails the hehavior that the user's preference of boot media
   order should be determined by Boot#### and BootOrder variables.

With this patch, the semantics mentioned above is fully implemented.
For example, if you want to boot the system from USB and SCSI in this
order,
* define Boot0001 which contains only a device path to the USB device
  (without any file path/name)
* define Boot0002 which contains only a device path to the SCSI device,
and
* set BootOrder to Boot0001:Boot0002

To avoid build error for sandbox, default file name "BOOTSANDBOX.efi"
is defined even if it is out of scope of UEFI specification.

Signed-off-by: AKASHI Takahiro <[email protected]>
Signed-off-by: Masahisa Kojima <[email protected]>
On sandbox use binary name corresponding to host architecture.
Reviewed-by: Heinrich Schuchardt <[email protected]>

1 files changed, 45 insertions, 0 deletions

diff --git a/include/efi_default_filename.h b/include/efi_default_filename.h
new file mode 100644
index 00000000000..13b9de8754a
--- /dev/null
+++ b/include/efi_default_filename.h
@@ -0,0 +1,45 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * When a boot option does not provide a file path the EFI file to be
+ * booted is \EFI\BOOT\$(BOOTEFI_NAME).EFI. The architecture specific
+ * file name is defined in this include.
+ *
+ * Copyright (c) 2022, Heinrich Schuchardt <[email protected]>
+ */
+
+#ifndef _EFI_DEFAULT_FILENAME_H
+#define _EFI_DEFAULT_FILENAME_H
+
+#include <host_arch.h>
+
+#undef BOOTEFI_NAME
+
+#if HOST_ARCH == HOST_ARCH_X86_64
+#define BOOTEFI_NAME "BOOTX64.EFI"
+#endif
+
+#if HOST_ARCH == HOST_ARCH_X86
+#define BOOTEFI_NAME "BOOTIA32.EFI"
+#endif
+
+#if HOST_ARCH == HOST_ARCH_AARCH64
+#define BOOTEFI_NAME "BOOTAA64.EFI"
+#endif
+
+#if HOST_ARCH == HOST_ARCH_ARM
+#define BOOTEFI_NAME "BOOTARM.EFI"
+#endif
+
+#if HOST_ARCH == HOST_ARCH_RISCV32
+#define BOOTEFI_NAME "BOOTRISCV32.EFI"
+#endif
+
+#if HOST_ARCH == HOST_ARCH_RISCV64
+#define BOOTEFI_NAME "BOOTRISCV64.EFI"
+#endif
+
+#ifndef BOOTEFI_NAME
+#error Unsupported UEFI architecture
+#endif
+
+#endif