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loader/efi/fdt: Add fdtdump command to access device tree

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The fdtdump command allows dumping arbitrary device tree properties
and saving them to a variable similar to the smbios command.

This is useful in scripts where further actions such as selecting
a kernel or loading another device tree depend on the compatible
or model values of the device tree provided by the firmware.

For now only the root level properties of the dtb are exposed.

Signed-off-by: Tobias Heider <tobias.heider@canonical.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This commit is contained in:
Tobias Heider 2024-06-17 17:10:26 +02:00 committed by Daniel Kiper
parent 0cfec355d0
commit ab9fe80300
2 changed files with 72 additions and 0 deletions
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26
docs/grub.texi
View File

@ -4373,6 +4373,7 @@ you forget a command, you can run the command @command{help}
* eval:: Evaluate agruments as GRUB commands
* export:: Export an environment variable
* false:: Do nothing, unsuccessfully
* fdtdump:: Retrieve device tree information
* fwsetup:: Reboot into the firmware setup menu
* gdbinfo:: Provide info for debugging with GDB
* gettext:: Translate a string
@ -4904,6 +4905,31 @@ such as @code{if} and @code{while} (@pxref{Shell-like scripting}).
@end deffn
@node fdtdump
@subsection fdtdump
@deffn Command fdtdump @
[@option{--prop} @var{prop}] @
[@option{--set} @var{variable}]
Retrieve device tree information.
The @command{fdtdump} command returns the value of a property in the device
tree provided by the firmware. The @option{--prop} option determines which
property to select.
The default action is to print the value of the requested field to the console,
but a variable name can be specified with @option{--set} to store the value
instead of printing it.
For example, this will store and then display the model string.
@example
fdtdump --prop model --set machine_model
echo $machine_model
@end example
@end deffn
@node fwsetup
@subsection fwsetup

46
grub-core/loader/efi/fdt.c
View File

@ -1,6 +1,7 @@
/*
* GRUB -- GRand Unified Bootloader
* Copyright (C) 2013-2015 Free Software Foundation, Inc.
* Copyright (C) 2024 Canonical, Ltd.
*
* GRUB is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
@ -18,9 +19,11 @@
#include <grub/fdt.h>
#include <grub/mm.h>
#include <grub/env.h>
#include <grub/err.h>
#include <grub/dl.h>
#include <grub/command.h>
#include <grub/extcmd.h>
#include <grub/file.h>
#include <grub/efi/efi.h>
#include <grub/efi/fdtload.h>
@ -36,6 +39,13 @@ static void *fdt;
sizeof (FDT_ADDR_CELLS_STRING) + \
sizeof (FDT_SIZE_CELLS_STRING))
static const struct grub_arg_option options_fdtdump[] = {
{"prop", 'p', 0, N_("Get property."), N_("prop"), ARG_TYPE_STRING},
{"set", '\0', 0, N_("Store the value in the given variable name."),
N_("variable"), ARG_TYPE_STRING},
{0, 0, 0, 0, 0, 0}
};
void *
grub_fdt_load (grub_size_t additional_size)
{
@ -167,10 +177,45 @@ out:
return grub_errno;
}
static grub_err_t
grub_cmd_fdtdump (grub_extcmd_context_t ctxt,
int argc __attribute__ ((unused)),
char **argv __attribute__ ((unused)))
{
struct grub_arg_list *state = ctxt->state;
const char *value = NULL;
void *fw_fdt;
fw_fdt = grub_efi_get_firmware_fdt ();
if (fw_fdt == NULL)
return grub_error (GRUB_ERR_IO,
N_("No device tree found"));
if (state[0].set)
value = grub_fdt_get_prop (fw_fdt, 0, state[0].arg, NULL);
if (value == NULL)
return grub_error (GRUB_ERR_OUT_OF_RANGE,
N_("failed to retrieve the prop field"));
if (state[1].set)
grub_env_set (state[1].arg, value);
else
grub_printf ("%s\n", value);
return GRUB_ERR_NONE;
}
static grub_command_t cmd_devicetree;
static grub_extcmd_t cmd_fdtdump;
GRUB_MOD_INIT (fdt)
{
cmd_fdtdump =
grub_register_extcmd ("fdtdump", grub_cmd_fdtdump, 0,
N_("[-p] [--set variable]"),
N_("Retrieve device tree information."),
options_fdtdump);
cmd_devicetree =
grub_register_command_lockdown ("devicetree", grub_cmd_devicetree, 0,
N_("Load DTB file."));
@ -179,4 +224,5 @@ GRUB_MOD_INIT (fdt)
GRUB_MOD_FINI (fdt)
{
grub_unregister_command (cmd_devicetree);
grub_unregister_extcmd (cmd_fdtdump);
}