[RFC 2/3] efi_loader: bootmgr: add booting from removable media

[AKASHI Takahiro <takahiro.akashi@linaro.org>]

Under the current implementation, booting from removal 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

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
---
 lib/efi_loader/efi_bootmgr.c | 65 +++++++++++++++++++++++++++++++++++-
 1 file changed, 64 insertions(+), 1 deletion(-)

diff --git a/lib/efi_loader/efi_bootmgr.c b/lib/efi_loader/efi_bootmgr.c
index 1fe19237f9a6..1d9d5858561f 100644
--- a/lib/efi_loader/efi_bootmgr.c
+++ b/lib/efi_loader/efi_bootmgr.c
@@ -30,6 +30,66 @@ static const struct efi_runtime_services *rs;
  * should do normal or recovery boot.
  */
 
+#if defined(CONFIG_ARM64)
+#define BOOTEFI_NAME "bootaa64.efi"
+#elif defined(CONFIG_ARM)
+#define BOOTEFI_NAME "bootarm.efi"
+#elif defined(CONFIG_X86_RUN_32BIT)
+#define BOOTEFI_NAME "bootia32.efi"
+#elif defined(CONFIG_X86_RUN_64BIT)
+#define BOOTEFI_NAME "bootx64.efi"
+#elif defined(CONFIG_ARCH_RV32I)
+#define BOOTEFI_NAME "bootriscv32.efi"
+#elif defined(CONFIG_ARCH_RV64I)
+#define BOOTEFI_NAME "bootriscv64.efi"
+#else
+#define BOOTEFI_NAME "dummy.efi"
+#endif
+
+/**
+ * expand_media_path() - expand a device path for default file name
+ * @device_path:	device path to check against
+ *
+ * If @device_path is a media or disk partition which houses a file
+ * system, this function returns a full device path which contains
+ * an architecture-specific default file name for removable media.
+ *
+ * Return:	a newly allocated device path
+ */
+static
+struct efi_device_path *expand_media_path(struct efi_device_path *device_path)
+{
+	struct efi_device_path *dp, *full_path;
+	efi_handle_t handle;
+	efi_status_t ret;
+
+	if (!device_path)
+		return NULL;
+
+	/*
+	 * If device_path is a (removable) media or partition which provides
+	 * simple file system protocol, append a default file name to support
+	 * booting from removable media.
+	 */
+	dp = device_path;
+	ret = efi_locate_device_path(&efi_simple_file_system_protocol_guid,
+				     &dp, &handle);
+	if (ret == EFI_SUCCESS) {
+		if (dp->type == DEVICE_PATH_TYPE_END) {
+			dp = efi_dp_from_file(NULL, 0,
+					      "/efi/boot/" BOOTEFI_NAME);
+			full_path = efi_dp_append(device_path, dp);
+		} else {
+			full_path = efi_dp_dup(device_path);
+		}
+		efi_free_pool(dp);
+	} else {
+		full_path = efi_dp_dup(device_path);
+	}
+
+	return full_path;
+}
+
 /**
  * try_load_entry() - try to load image for boot option
  *
@@ -68,13 +128,16 @@ static efi_status_t try_load_entry(u16 n, efi_handle_t *handle,
 	}
 
 	if (lo.attributes & LOAD_OPTION_ACTIVE) {
+		struct efi_device_path *file_path;
 		u32 attributes;
 
 		log_debug("%s: trying to load \"%ls\" from %pD\n",
 			  __func__, lo.label, lo.file_path);
 
-		ret = EFI_CALL(efi_load_image(true, efi_root, lo.file_path,
+		file_path = expand_media_path(lo.file_path);
+		ret = EFI_CALL(efi_load_image(true, efi_root, file_path,
 					      NULL, 0, handle));
+		efi_free_pool(file_path);
 		if (ret != EFI_SUCCESS) {
 			log_warning("Loading %ls '%ls' failed\n",
 				    varname, lo.label);
-- 
2.33.0