Re: [PATCH v5 7/8] Add a module for the Boot Loader Interface

[Daniel Kiper]

On Thu, Mar 30, 2023 at 01:18:12PM +0200, Oliver Steffen wrote:
> Add a new module named boot_loader_interface, which provides a command

s/boot_loader_interface/bli/?

> with the same name. It implements a small but quite useful part of the
> Boot Loader Interface [0].  This interface uses EFI variables for
> communication between the boot loader and the operating system.
>
> This module sets two EFI variables under the vendor GUID
> 4a67b082-0a4c-41cf-b6c7-440b29bb8c4f:
>
> - LoaderInfo: contains GRUB + <version number>.
>   This allows the running operating system to identify the boot loader
>   used during boot.
>
> - LoaderDevicePartUUID: contains the partition UUID of the
>   EFI System Partition (ESP).  This is used by
>   systemd-gpt-auto-generator [1] to find the root partitions (and others
>   too), via partition type IDs [2].
>
> This module is only available on EFI platforms.
>
> [0] https://systemd.io/BOOT_LOADER_INTERFACE/
> [1] 
> https://www.freedesktop.org/software/systemd/man/systemd-gpt-auto-generator.html
> [2] 
> https://uapi-group.org/specifications/specs/discoverable_partitions_specification/
>
> Signed-off-by: Oliver Steffen <osteffen@redhat.com>
> ---
>  docs/grub.texi              |  22 +++++
>  grub-core/Makefile.core.def |   6 ++
>  grub-core/commands/bli.c    | 166 ++++++++++++++++++++++++++++++++++++
>  include/grub/efi/api.h      |   5 ++
>  4 files changed, 199 insertions(+)
>  create mode 100644 grub-core/commands/bli.c
>
> diff --git a/docs/grub.texi b/docs/grub.texi
> index a3e9ce2d1..2fe8756a5 100644
> --- a/docs/grub.texi
> +++ b/docs/grub.texi
> @@ -4291,6 +4291,7 @@ you forget a command, you can run the command 
> @command{help}
>  * background_image::            Load background image for active terminal
>  * badram::                      Filter out bad regions of RAM
>  * blocklist::                   Print a block list
> +* bli::                         Set Boot Loader Interface EFI variables
>  * boot::                        Start up your operating system
>  * cat::                         Show the contents of a file
>  * clear::                       Clear the screen
> @@ -4471,6 +4472,27 @@ Print a block list (@pxref{Block list syntax}) for 
> @var{file}.
>  @end deffn
>
>
> +@node bli
> +@subsection bli
> +
> +@deffn Command bli
> +Initialize the @url{https://systemd.io/BOOT_LOADER_INTERFACE/, Boot Loader 
> Interface}.
> +
> +This command sets two EFI variables under the vendor GUID
> +@code{4a67b082-0a4c-41cf-b6c7-440b29bb8c4f}:
> +
> +@code{LoaderDevicePartUUID} is set to the Partition UUID of the EFI System 
> Partition used during boot.
> +This is needed for automatic partition discovery as described by the
> +@url{https://uapi-group.org/specifications/specs/discoverable_partitions_specification/,
> +Discoverable Partitions Specification}.
> +
> +@code{LoaderInfo} is set to the string @code{Grub} followed by the version 
> number.  This is used by
> +user-space tools to identify the boot loader that was used.
> +
> +This command is only available on UEFI platforms.

Please move "only" to the end of the sentence.

> +@end deffn
> +
> +
>  @node boot
>  @subsection boot
>
> diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
> index 801df7c21..b77375857 100644
> --- a/grub-core/Makefile.core.def
> +++ b/grub-core/Makefile.core.def
> @@ -2561,3 +2561,9 @@ module = {
>    common = commands/memtools.c;
>    condition = COND_MM_DEBUG;
>  };
> +
> +module = {
> +  name = bli;
> +  efi = commands/bli.c;
> +  enable = efi;
> +};
> diff --git a/grub-core/commands/bli.c b/grub-core/commands/bli.c
> new file mode 100644
> index 000000000..3ce0161a8
> --- /dev/null
> +++ b/grub-core/commands/bli.c
> @@ -0,0 +1,166 @@
> +/*
> + *  GRUB  --  GRand Unified Bootloader
> + *  Copyright (C) 2023  Free Software Foundation, Inc.
> + *
> + *  GRUB is free software: you can redistribute it and/or modify
> + *  it under the terms of the GNU General Public License as published by
> + *  the Free Software Foundation, either version 3 of the License, or
> + *  (at your option) any later version.
> + *
> + *  GRUB is distributed in the hope that it will be useful,
> + *  but WITHOUT ANY WARRANTY; without even the implied warranty of
> + *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + *  GNU General Public License for more details.
> + *
> + *  You should have received a copy of the GNU General Public License
> + *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
> + *
> + *  Implementation of the Boot Loader Interface.
> + */
> +
> +#include <grub/charset.h>
> +#include <grub/efi/api.h>
> +#include <grub/efi/disk.h>
> +#include <grub/efi/efi.h>
> +#include <grub/err.h>
> +#include <grub/extcmd.h>
> +#include <grub/gpt_partition.h>
> +#include <grub/misc.h>
> +#include <grub/mm.h>
> +#include <grub/partition.h>
> +#include <grub/types.h>
> +
> +GRUB_MOD_LICENSE ("GPLv3+");
> +
> +#define MODNAME "bli"
> +
> +static const grub_guid_t bli_vendor_guid = 
> GRUB_EFI_VENDOR_BOOT_LOADER_INTERFACE_GUID;
> +
> +static grub_err_t
> +get_part_uuid (const char *device_name, char **part_uuid)
> +{
> +  grub_device_t device;
> +  grub_err_t status = GRUB_ERR_NONE;
> +  grub_disk_t disk = NULL;
> +  struct grub_gpt_partentry entry;
> +
> +  device = grub_device_open (device_name);
> +  if (device == NULL)
> +    {
> +      status = grub_error (grub_errno, N_("error opening device: %s"), 
> device_name);

s/error opening device/cannot open device/

Otherwise you will see following error message:

  error: error opening device: ...

🤔

> +      goto fail;
> +    }
> +
> +  disk = grub_disk_open (device->disk->name);
> +  if (disk == NULL)
> +    {
> +      status = grub_error (grub_errno, N_("error opening disk: %s"), 
> device_name);

s/error opening disk/cannot open disk/

> +      return status;
> +    }
> +
> +  if (grub_strcmp (device->disk->partition->partmap->name, "gpt") != 0)
> +    {
> +      status = grub_error (GRUB_ERR_BAD_PART_TABLE,
> +                        N_("this is not a GPT partition table: %s"), 
> device_name);
> +      goto fail;
> +    }
> +
> +  if (grub_disk_read (disk, device->disk->partition->offset,
> +                   device->disk->partition->index, sizeof (entry), &entry) 
> != GRUB_ERR_NONE)
> +    {
> +      status = grub_error (grub_errno, N_("read error: %s"), device_name);
> +      goto fail;
> +    }
> +
> +  *part_uuid = grub_xasprintf ("%pG", &entry.guid);
> +  if (*part_uuid == NULL)
> +    status = grub_errno;
> +
> + fail:
> +  grub_disk_close (disk);
> +  grub_device_close (device);
> +
> +  return status;
> +}
> +
> +static grub_err_t
> +set_efi_str_variable (const char *name, const grub_guid_t *guid,
> +                      const char *value)

This function looks pretty generic and I have an itching to move it to
the GRUB EFI common code. Could you do that?

> +{
> +  grub_efi_char16_t *value_16;
> +  grub_ssize_t len16;
> +  grub_err_t status;
> +
> +  len16 = grub_utf8_to_utf16_alloc (value, &value_16, NULL);
> +
> +  if (len16 < 0)
> +    return grub_errno;
> +
> +  status = grub_efi_set_variable_with_attributes (name, guid,
> +                     (void *) value_16, (len16 + 1) * sizeof (value_16[0]),
> +                     GRUB_EFI_VARIABLE_BOOTSERVICE_ACCESS | 
> GRUB_EFI_VARIABLE_RUNTIME_ACCESS);
> +
> +  grub_free (value_16);
> +
> +  return status;
> +}

Daniel