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

From: AKASHI Takahiro takahiro.akashi@linaro.org Date: Tue, 9 Nov 2021 10:32:32 +0900

Hi Takahiro,

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

The problem with this approach is that EFI device paths are complicated things and I don't think we can expect users to do what you describe above all by hand. All x86 machines I've seen have a more user-friendly way to configure the desired boot order, and also a way to specify which device to boot from after automatic boot has been interrupted.

With the current distroboot scripts one can simply do:

setenv boot_targets usb0 mmc0 pxe dhcp

and I think we need to have something simple like that. Maybe the code can automatically create Boot#### and BootOrder variables based on the boot_targets environment variables if they're not defined?

Another idea is to accept U-Boot device names (e.g. usb0, mmc0) as aliases for EFI device paths and automatically expand them?

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