Re: [PATCH 1/2] loader/efi/fdt: Add fdtdump command to access device tree

[Tobias Heider]

On Fri, Jun 14, 2024 at 06:03:23PM +0200, Daniel Kiper wrote:
> On Wed, Jun 12, 2024 at 01:12:28PM +0200, Tobias Heider 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.
> >
> > Signed-off-by: Tobias Heider <tobias.heider@canonical.com>
> > ---
> >  grub-core/loader/efi/fdt.c | 51 +++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 50 insertions(+), 1 deletion(-)
> >
> > diff --git a/grub-core/loader/efi/fdt.c b/grub-core/loader/efi/fdt.c
> > index 439964b9c..8fa0b3b09 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;
> 
> This change seems suspicious for me. Could you explain why it is needed?

Since I added grub_efi_get_firmware_fdt() to module init function and the
device tree passed by the firmware is a fairly static property it made
sense to me to use the address we have instead of rereading it in 
grub_fdt_load().

If you are more comfortable if I don't touch that code path I can drop that
change and simply read it twice.

> 
> >    if (raw_fdt)
> >        size = grub_fdt_get_totalsize (raw_fdt);
> > @@ -167,10 +178,47 @@ 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);
> 
> Missing space before "(".
> 
> > +    }
> 
> Please drop redundant curly braces.

Thanks for the review, I'll send an update with those fixed and the two commits 
merged.

> 
> > +  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;
> > +}
> 
> Daniel