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Re: [PATCH v2] loader/efi/fdt: Add fdtdump command to access device tree
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From: |
Vladimir 'phcoder' Serbinenko |
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Subject: |
Re: [PATCH v2] loader/efi/fdt: Add fdtdump command to access device tree |
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Date: |
Mon, 17 Jun 2024 16:43:22 +0300 |
Saving FDT subtly changes the behaviour. Image some command or even an
external program modifying FDT and freeing old copy. Maybe we should
call grub_efi_get_firmware_fdt every time we need fdt.
On Mon, Jun 17, 2024 at 4:08 PM Tobias Heider
<tobias.heider@canonical.com> wrote:
>
> 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.
>
> The firmware provided device-tree is not expected to change so we
> load it once during module initialization and then use it where
> needed.
>
> Signed-off-by: Tobias Heider <tobias.heider@canonical.com>
> ---
> docs/grub.texi | 26 ++++++++++++++++++++
> grub-core/loader/efi/fdt.c | 49 +++++++++++++++++++++++++++++++++++++-
> 2 files changed, 74 insertions(+), 1 deletion(-)
>
> diff --git a/docs/grub.texi b/docs/grub.texi
> index f3bdc2564..a050dc0fc 100644
> --- a/docs/grub.texi
> +++ b/docs/grub.texi
> @@ -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
>
> diff --git a/grub-core/loader/efi/fdt.c b/grub-core/loader/efi/fdt.c
> index 439964b9c..cb0422d98 100644
> --- a/grub-core/loader/efi/fdt.c
> +++ b/grub-core/loader/efi/fdt.c
> @@ -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
> @@ -18,15 +19,18 @@
>
> #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>
> #include <grub/efi/memory.h>
> #include <grub/cpu/efi/memory.h>
>
> +static void *fw_fdt;
> static void *loaded_fdt;
> static void *fdt;
>
> @@ -36,6 +40,13 @@ 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)
> {
> @@ -51,7 +62,7 @@ grub_fdt_load (grub_size_t additional_size)
> if (loaded_fdt)
> raw_fdt = loaded_fdt;
> else
> - raw_fdt = grub_efi_get_firmware_fdt();
> + raw_fdt = fw_fdt;
>
> if (raw_fdt)
> size = grub_fdt_get_totalsize (raw_fdt);
> @@ -167,10 +178,45 @@ 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;
> +
> + 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)
> {
> + fw_fdt = grub_efi_get_firmware_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 +225,5 @@ GRUB_MOD_INIT (fdt)
> GRUB_MOD_FINI (fdt)
> {
> grub_unregister_command (cmd_devicetree);
> + grub_unregister_extcmd (cmd_fdtdump);
> }
> --
> 2.43.0
>
>
> _______________________________________________
> Grub-devel mailing list
> Grub-devel@gnu.org
> https://lists.gnu.org/mailman/listinfo/grub-devel
--
Regards
Vladimir 'phcoder' Serbinenko