Re: [PATCH v4 06/11] efi_loader: bootmgr: add booting from removable media

[Ilias Apalodimas <ilias.apalodimas@linaro.org>]

Hello Akashi-san,

On Thu, Mar 24, 2022 at 10:54:38PM +0900, Masahisa Kojima wrote:
> From: AKASHI Takahiro <takahiro.akashi@linaro.org>
> 
> 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

Mark had some concerns wrt to this approach and from what I can tell this
hasn't changed in this revision [1]. Can we use boot_targets and generate
Boot#### with an empty FilePath as Mark suggested?  Or is the user expected to
select that somehow from the menu?

[1] https://lore.kernel.org/u-boot/d3cac2e5b37f96b5@bloch.sibelius.xs4all.nl/

Thanks
/Ilias
> 
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
> ---
> Changes from original version:
> - create new include file "efi_default_filename.h" to
>   avoid conflict with config_distro_bootcmd.h
> - modify the target pointer of efi_free_pool(), expand_media_path() should
>   only free the pointer allocated by efi_dp_from_file() function.
> 
>  include/config_distro_bootcmd.h | 14 +--------
>  include/efi_default_filename.h  | 26 +++++++++++++++++
>  lib/efi_loader/efi_bootmgr.c    | 50 ++++++++++++++++++++++++++++++++-
>  3 files changed, 76 insertions(+), 14 deletions(-)
>  create mode 100644 include/efi_default_filename.h
> 
> diff --git a/include/config_distro_bootcmd.h b/include/config_distro_bootcmd.h
> index 2f90929178..ef2c9f330e 100644
> --- a/include/config_distro_bootcmd.h
> +++ b/include/config_distro_bootcmd.h
> @@ -91,19 +91,7 @@
>  #endif
>  
>  #ifdef CONFIG_EFI_LOADER
> -#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"
> -#endif
> +#include <efi_default_filename.h>
>  #endif
>  
>  #ifdef BOOTEFI_NAME
> diff --git a/include/efi_default_filename.h b/include/efi_default_filename.h
> new file mode 100644
> index 0000000000..de030d2692
> --- /dev/null
> +++ b/include/efi_default_filename.h
> @@ -0,0 +1,26 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +/*
> + * Default boot file name when none is present in the FilePath.
> + *
> + * Copyright (c) 2022, Linaro Limited
> + */
> +#ifndef _EFI_DEFAULT_FILENAME_H
> +#define _EFI_DEFAULT_FILENAME_H
> +
> +#if defined(CONFIG_ARM64)
> +#define BOOTEFI_NAME "BOOTAA64.EFI"
> +#elif defined(CONFIG_ARM)
> +#define BOOTEFI_NAME "BOOTARM.EFI"
> +#elif defined(CONFIG_X86_64)
> +#define BOOTEFI_NAME "BOOTX64.EFI"
> +#elif defined(CONFIG_X86)
> +#define BOOTEFI_NAME "BOOTIA32.EFI"
> +#elif defined(CONFIG_ARCH_RV32I)
> +#define BOOTEFI_NAME "BOOTRISCV32.EFI"
> +#elif defined(CONFIG_ARCH_RV64I)
> +#define BOOTEFI_NAME "BOOTRISCV64.EFI"
> +#else
> +#error Unsupported UEFI architecture
> +#endif
> +
> +#endif
> diff --git a/lib/efi_loader/efi_bootmgr.c b/lib/efi_loader/efi_bootmgr.c
> index 8c04ecbdc8..22a4302aac 100644
> --- a/lib/efi_loader/efi_bootmgr.c
> +++ b/lib/efi_loader/efi_bootmgr.c
> @@ -11,6 +11,7 @@
>  #include <charset.h>
>  #include <log.h>
>  #include <malloc.h>
> +#include <efi_default_filename.h>
>  #include <efi_loader.h>
>  #include <efi_variable.h>
>  #include <asm/unaligned.h>
> @@ -30,6 +31,50 @@ static const struct efi_runtime_services *rs;
>   * should do normal or recovery boot.
>   */
>  
> +/**
> + * 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);
> +			efi_free_pool(dp);
> +		} else {
> +			full_path = efi_dp_dup(device_path);
> +		}
> +	} else {
> +		full_path = efi_dp_dup(device_path);
> +	}
> +
> +	return full_path;
> +}
> +
>  /**
>   * try_load_entry() - try to load image for boot option
>   *
> @@ -68,13 +113,16 @@ 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);
> -- 
> 2.17.1
>