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From: Masahiro Yamada <masahiroy@kernel.org>
Date: Sun, 25 Feb 2024 17:40:39 +0900
Message-ID: <CAK7LNASFR4XtyNKDtMabm6gd+oeMefZsg4nDMaY+Qmg2KkN8ew@mail.gmail.com>
Subject: Re: [PATCH v10 2/2] arm64: boot: Support Flat Image Tree
To: Simon Glass <sjg@chromium.org>
Cc: linux-arm-kernel@lists.infradead.org, 
	Ahmad Fatoum <a.fatoum@pengutronix.de>, Nicolas Schier <nicolas@fjasle.eu>, 
	Catalin Marinas <catalin.marinas@arm.com>, Jonathan Corbet <corbet@lwn.net>, 
	Nathan Chancellor <nathan@kernel.org>, Nick Terrell <terrelln@fb.com>, Will Deacon <will@kernel.org>, 
	linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org, 
	linux-kernel@vger.kernel.org, workflows@vger.kernel.org
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On Wed, Feb 21, 2024 at 9:37=E2=80=AFPM Masahiro Yamada <masahiroy@kernel.o=
rg> wrote:
>
> On Sat, Feb 3, 2024 at 2:30=E2=80=AFAM Simon Glass <sjg@chromium.org> wro=
te:
> >
> > Add a script which produces a Flat Image Tree (FIT), a single file
> > containing the built kernel and associated devicetree files.
> > Compression defaults to gzip which gives a good balance of size and
> > performance.
> >
> > The files compress from about 86MB to 24MB using this approach.
> >
> > The FIT can be used by bootloaders which support it, such as U-Boot
> > and Linuxboot. It permits automatic selection of the correct
> > devicetree, matching the compatible string of the running board with
> > the closest compatible string in the FIT. There is no need for
> > filenames or other workarounds.
> >
> > Add a 'make image.fit' build target for arm64, as well.
> >
> > The FIT can be examined using 'dumpimage -l'.
> >
> > This uses the 'dtbs-list' file but processes only .dtb files, ignoring
> > the overlay .dtbo files.
> >
> > This features requires pylibfdt (use 'pip install libfdt'). It also
> > requires compression utilities for the algorithm being used. Supported
> > compression options are the same as the Image.xxx files. Use
> > FIT_COMPRESSION to select an algorithm other than gzip.
> >
> > While FIT supports a ramdisk / initrd, no attempt is made to support
> > this here, since it must be built separately from the Linux build.
> >
> > Signed-off-by: Simon Glass <sjg@chromium.org>
> > ---
> >
> > Changes in v10:
> > - Make use of dtbs-list file
> > - Mention dtbs-list and FIT_COMPRESSION
> > - Update copyright year
> > - Update cover letter to take account of an applied patch
> >
> > Changes in v9:
> > - Move the compression control into Makefile.lib
> >
> > Changes in v8:
> > - Drop compatible string in FDT node
> > - Correct sorting of MAINTAINERS to before ARM64 PORT
> > - Turn compress part of the make_fit.py comment in to a sentence
> > - Add two blank lines before parse_args() and setup_fit()
> > - Use 'image.fit: dtbs' instead of BUILD_DTBS var
> > - Use '$(<D)/dts' instead of '$(dir $<)dts'
> > - Add 'mkimage' details Documentation/process/changes.rst
> > - Allow changing the compression used
> > - Tweak cover letter since there is only one clean-up patch
> >
> > Changes in v7:
> > - Add Image as a dependency of image.fit
> > - Drop kbuild tag
> > - Add dependency on dtbs
> > - Drop unnecessary path separator for dtbs
> > - Rebase to -next
> >
> > Changes in v5:
> > - Drop patch previously applied
> > - Correct compression rule which was broken in v4
> >
> > Changes in v4:
> > - Use single quotes for UIMAGE_NAME
> >
> > Changes in v3:
> > - Drop temporary file image.itk
> > - Drop patch 'Use double quotes for image name'
> > - Drop double quotes in use of UIMAGE_NAME
> > - Drop unnecessary CONFIG_EFI_ZBOOT condition for help
> > - Avoid hard-coding "arm64" for the DT architecture
> >
> > Changes in v2:
> > - Drop patch previously applied
> > - Add .gitignore file
> > - Move fit rule to Makefile.lib using an intermediate file
> > - Drop dependency on CONFIG_EFI_ZBOOT
> > - Pick up .dtb files separately from the kernel
> > - Correct pylint too-many-args warning for write_kernel()
> > - Include the kernel image in the file count
> > - Add a pointer to the FIT spec and mention of its wide industry usage
> > - Mention the kernel version in the FIT description
> >
> >  Documentation/process/changes.rst |   9 +
> >  MAINTAINERS                       |   7 +
> >  arch/arm64/Makefile               |   7 +-
> >  arch/arm64/boot/.gitignore        |   1 +
> >  arch/arm64/boot/Makefile          |   6 +-
> >  scripts/Makefile.lib              |  16 ++
> >  scripts/make_fit.py               | 298 ++++++++++++++++++++++++++++++
> >  7 files changed, 341 insertions(+), 3 deletions(-)
> >  create mode 100755 scripts/make_fit.py
> >
> > diff --git a/Documentation/process/changes.rst b/Documentation/process/=
changes.rst
> > index 50b3d1cb1115..a8110965e4e1 100644
> > --- a/Documentation/process/changes.rst
> > +++ b/Documentation/process/changes.rst
> > @@ -62,6 +62,7 @@ Sphinx\ [#f1]_         2.4.4            sphinx-build =
--version
> >  cpio                   any              cpio --version
> >  GNU tar                1.28             tar --version
> >  gtags (optional)       6.6.5            gtags --version
> > +mkimage (optional)     2017.01          mkimage --version
> >  =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D  =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
> >
> >  .. [#f1] Sphinx is needed only to build the Kernel documentation
> > @@ -189,6 +190,14 @@ The kernel build requires GNU GLOBAL version 6.6.5=
 or later to generate
> >  tag files through ``make gtags``.  This is due to its use of the gtags
> >  ``-C (--directory)`` flag.
> >
> > +mkimage
> > +-------
> > +
> > +This tool is used when building a Flat Image Tree (FIT), commonly used=
 on ARM
> > +platforms. The tool is available via the ``u-boot-tools`` package or c=
an be
> > +built from the U-Boot source code. See the instructions at
> > +https://docs.u-boot.org/en/latest/build/tools.html#building-tools-for-=
linux
> > +
> >  System utilities
> >  ****************
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 61117c3afa80..10c2753d7bcc 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -3026,6 +3026,13 @@ F:       drivers/mmc/host/sdhci-of-arasan.c
> >  N:     zynq
> >  N:     xilinx
> >
> > +ARM64 FIT SUPPORT
> > +M:     Simon Glass <sjg@chromium.org>
> > +L:     linux-arm-kernel@lists.infradead.org (moderated for non-subscri=
bers)
> > +S:     Maintained
> > +F:     arch/arm64/boot/Makefile
> > +F:     scripts/make_fit.py
> > +
> >  ARM64 PORT (AARCH64 ARCHITECTURE)
> >  M:     Catalin Marinas <catalin.marinas@arm.com>
> >  M:     Will Deacon <will@kernel.org>
> > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> > index 83cd2b7234b9..5de2b02f549a 100644
> > --- a/arch/arm64/Makefile
> > +++ b/arch/arm64/Makefile
> > @@ -150,7 +150,7 @@ libs-$(CONFIG_EFI_STUB) +=3D $(objtree)/drivers/fir=
mware/efi/libstub/lib.a
> >  # Default target when executing plain make
> >  boot           :=3D arch/arm64/boot
> >
> > -BOOT_TARGETS   :=3D Image vmlinuz.efi
> > +BOOT_TARGETS   :=3D Image vmlinuz.efi image.fit
> >
> >  PHONY +=3D $(BOOT_TARGETS)
> >
> > @@ -162,7 +162,9 @@ endif
> >
> >  all:   $(notdir $(KBUILD_IMAGE))
> >
> > -vmlinuz.efi: Image
> > +image.fit: dtbs
> > +
> > +vmlinuz.efi image.fit: Image
> >  $(BOOT_TARGETS): vmlinux
> >         $(Q)$(MAKE) $(build)=3D$(boot) $(boot)/$@
> >
> > @@ -215,6 +217,7 @@ virtconfig:
> >  define archhelp
> >    echo  '* Image.gz      - Compressed kernel image (arch/$(ARCH)/boot/=
Image.gz)'
> >    echo  '  Image         - Uncompressed kernel image (arch/$(ARCH)/boo=
t/Image)'
> > +  echo  '  image.fit     - Flat Image Tree (arch/$(ARCH)/boot/image.fi=
t)'
> >    echo  '  install       - Install uncompressed kernel'
> >    echo  '  zinstall      - Install compressed kernel'
> >    echo  '                  Install using (your) ~/bin/installkernel or=
'
> > diff --git a/arch/arm64/boot/.gitignore b/arch/arm64/boot/.gitignore
> > index af5dc61f8b43..abaae9de1bdd 100644
> > --- a/arch/arm64/boot/.gitignore
> > +++ b/arch/arm64/boot/.gitignore
> > @@ -2,3 +2,4 @@
> >  Image
> >  Image.gz
> >  vmlinuz*
> > +image.fit
> > diff --git a/arch/arm64/boot/Makefile b/arch/arm64/boot/Makefile
> > index a5a787371117..ab21af82913e 100644
> > --- a/arch/arm64/boot/Makefile
> > +++ b/arch/arm64/boot/Makefile
> > @@ -16,7 +16,8 @@
> >
> >  OBJCOPYFLAGS_Image :=3D-O binary -R .note -R .note.gnu.build-id -R .co=
mment -S
> >
> > -targets :=3D Image Image.bz2 Image.gz Image.lz4 Image.lzma Image.lzo I=
mage.zst
> > +targets :=3D Image Image.bz2 Image.gz Image.lz4 Image.lzma Image.lzo \
> > +       Image.zst image.fit
> >
> >  $(obj)/Image: vmlinux FORCE
> >         $(call if_changed,objcopy)
> > @@ -39,6 +40,9 @@ $(obj)/Image.lzo: $(obj)/Image FORCE
> >  $(obj)/Image.zst: $(obj)/Image FORCE
> >         $(call if_changed,zstd)
> >
> > +$(obj)/image.fit: $(obj)/Image FORCE
> > +       $(call cmd,fit)
>
>
>
> The point for using dtbs-list is
> to avoid rebuilding image.fit needlessly.
>
>
> This should be:
>
> $(obj)/image.fit: $(obj)/Image $(obj)/dts/dtbs-list FORCE
>         $(call if_changed,fit)
>
>
>
>
>
> > +
> >  EFI_ZBOOT_PAYLOAD      :=3D Image
> >  EFI_ZBOOT_BFD_TARGET   :=3D elf64-littleaarch64
> >  EFI_ZBOOT_MACH_TYPE    :=3D ARM64
> > diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> > index b35d39022a30..4efb5ad07fd7 100644
> > --- a/scripts/Makefile.lib
> > +++ b/scripts/Makefile.lib
> > @@ -502,6 +502,22 @@ quiet_cmd_uimage =3D UIMAGE  $@
> >                         -a $(UIMAGE_LOADADDR) -e $(UIMAGE_ENTRYADDR) \
> >                         -n '$(UIMAGE_NAME)' -d $< $@
> >
> > +# Flat Image Tree (FIT)
> > +# This allows for packaging of a kernel and all devicetrees files, usi=
ng
> > +# compression.
> > +# --------------------------------------------------------------------=
-------
> > +
> > +MAKE_FIT :=3D $(srctree)/scripts/make_fit.py
> > +
> > +# Use this to override the compression algorithm
> > +FIT_COMPRESSION ?=3D gzip
> > +
> > +quiet_cmd_fit =3D FIT     $@
> > +      cmd_fit =3D $(MAKE_FIT) -f $@ --arch $(UIMAGE_ARCH) --os linux \
> > +                       --name '$(UIMAGE_NAME)' \
> > +                       --compress $(FIT_COMPRESSION) -k $< \
> > +                       @arch/$(SRCARCH)/boot/dts/dtbs-list
>
>
>
>
> cmd_fit =3D $(MAKE_FIT) -f $@ --arch $(UIMAGE_ARCH) --os linux \
>                 --name '$(UIMAGE_NAME)' \
>                 --compress $(FIT_COMPRESSION) -k $< @$(word 2,$^)
>
>
>
>
>
> > +
> >  # XZ
> >  # --------------------------------------------------------------------=
-------
> >  # Use xzkern to compress the kernel image and xzmisc to compress other=
 things.
> > diff --git a/scripts/make_fit.py b/scripts/make_fit.py
> > new file mode 100755
> > index 000000000000..69eee32960ae
> > --- /dev/null
> > +++ b/scripts/make_fit.py
> > @@ -0,0 +1,298 @@
> > +#!/usr/bin/env python3
> > +# SPDX-License-Identifier: GPL-2.0+
> > +#
> > +# Copyright 2024 Google LLC
> > +# Written by Simon Glass <sjg@chromium.org>
> > +#
> > +
> > +"""Build a FIT containing a lot of devicetree files
> > +
> > +Usage:
> > +    make_fit.py -A arm64 -n 'Linux-6.6' -O linux
> > +        -f arch/arm64/boot/image.fit -k /tmp/kern/arch/arm64/boot/imag=
e.itk
> > +        @arch/arm64/boot/dts/dtbs-list -E -c gzip
> > +
> > +Creates a FIT containing the supplied kernel and a set of devicetree f=
iles,
> > +either specified individually or listed in a file (with an '@' prefix)=
 Files
> > +which don't end in '.dtb' are silently ignored.
>
>
> Why do you need to check the suffix?
>
>
>
> > +
> > +Use -E to generate an external FIT (where the data is placed after the
> > +FIT data structure). This allows parsing of the data without loading
> > +the entire FIT.
> > +
> > +Use -c to compress the data, using bzip2, gzip, lz4, lzma, lzo and
> > +zstd algorithms.
> > +
> > +The resulting FIT can be booted by bootloaders which support FIT, such
> > +as U-Boot, Linuxboot, Tianocore, etc.
> > +
> > +Note that this tool does not yet support adding a ramdisk / initrd.
> > +"""
> > +
> > +import argparse
> > +import collections
> > +import os
> > +import subprocess
> > +import sys
> > +import tempfile
> > +import time
> > +
> > +import libfdt
> > +
> > +
> > +# Tool extension and the name of the command-line tools
> > +CompTool =3D collections.namedtuple('CompTool', 'ext,tools')
> > +
> > +COMP_TOOLS =3D {
> > +    'bzip2': CompTool('.bz2', 'bzip2'),
> > +    'gzip': CompTool('.gz', 'pigz,gzip'),
> > +    'lz4': CompTool('.lz4', 'lz4'),
> > +    'lzma': CompTool('.lzma', 'lzma'),
> > +    'lzo': CompTool('.lzo', 'lzop'),
> > +    'zstd': CompTool('.zstd', 'zstd'),
> > +}
> > +
> > +
> > +def parse_args():
> > +    """Parse the program ArgumentParser
> > +
> > +    Returns:
> > +        Namespace object containing the arguments
> > +    """
> > +    epilog =3D 'Build a FIT from a directory tree containing .dtb file=
s'
> > +    parser =3D argparse.ArgumentParser(epilog=3Depilog)
> > +    parser.add_argument('-A', '--arch', type=3Dstr, required=3DTrue,
> > +          help=3D'Specifies the architecture')
> > +    parser.add_argument('-c', '--compress', type=3Dstr, default=3D'non=
e',
> > +          help=3D'Specifies the compression')
> > +    parser.add_argument('-E', '--external', action=3D'store_true',
> > +          help=3D'Convert the FIT to use external data')
> > +    parser.add_argument('-n', '--name', type=3Dstr, required=3DTrue,
> > +          help=3D'Specifies the name')
> > +    parser.add_argument('-O', '--os', type=3Dstr, required=3DTrue,
> > +          help=3D'Specifies the operating system')
> > +    parser.add_argument('-f', '--fit', type=3Dstr, required=3DTrue,
> > +          help=3D'Specifies the output file (.fit)')
>
>
>
> I like -o (--output) to specify the output file.
>
>
>
>     parser.add_argument('-o', '--output', type=3Dstr, required=3DTrue,
>              help=3D'Specifies the output file (.fit)')
>
>
>
>
>
> > +    parser.add_argument('-k', '--kernel', type=3Dstr, required=3DTrue,
> > +          help=3D'Specifies the (uncompressed) kernel input file (.itk=
)')
> > +    parser.add_argument('srcdir', type=3Dstr, nargs=3D'*',
> > +          help=3D'Specifies the directory tree that contains .dtb file=
s')
>
>
> srcdir?
>
> You changed the positional parameters to take dtb files.
>
>
>
>
>
>
> > +
> > +    return parser.parse_args()
> > +
> > +
> > +def setup_fit(fsw, name):
> > +    """Make a start on writing the FIT
> > +
> > +    Outputs the root properties and the 'images' node
> > +
> > +    Args:
> > +        fsw (libfdt.FdtSw): Object to use for writing
> > +        name (str): Name of kernel image
> > +    """
> > +    fsw.INC_SIZE =3D 65536
> > +    fsw.finish_reservemap()
> > +    fsw.begin_node('')
> > +    fsw.property_string('description', f'{name} with devicetree set')
> > +    fsw.property_u32('#address-cells', 1)
> > +
> > +    fsw.property_u32('timestamp', int(time.time()))
> > +    fsw.begin_node('images')
> > +
> > +
> > +def write_kernel(fsw, data, args):
> > +    """Write out the kernel image
> > +
> > +    Writes a kernel node along with the required properties
> > +
> > +    Args:
> > +        fsw (libfdt.FdtSw): Object to use for writing
> > +        data (bytes): Data to write (possibly compressed)
> > +        args (Namespace): Contains necessary strings:
> > +            arch: FIT architecture, e.g. 'arm64'
> > +            fit_os: Operating Systems, e.g. 'linux'
> > +            name: Name of OS, e.g. 'Linux-6.6.0-rc7'
> > +            compress: Compression algorithm to use, e.g. 'gzip'
> > +    """
> > +    with fsw.add_node('kernel'):
> > +        fsw.property_string('description', args.name)
> > +        fsw.property_string('type', 'kernel_noload')
> > +        fsw.property_string('arch', args.arch)
> > +        fsw.property_string('os', args.os)
> > +        fsw.property_string('compression', args.compress)
> > +        fsw.property('data', data)
> > +        fsw.property_u32('load', 0)
> > +        fsw.property_u32('entry', 0)
> > +
> > +
> > +def finish_fit(fsw, entries):
> > +    """Finish the FIT ready for use
> > +
> > +    Writes the /configurations node and subnodes
> > +
> > +    Args:
> > +        fsw (libfdt.FdtSw): Object to use for writing
> > +        entries (list of tuple): List of configurations:
> > +            str: Description of model
> > +            str: Compatible stringlist
> > +    """
> > +    fsw.end_node()
> > +    seq =3D 0
> > +    with fsw.add_node('configurations'):
> > +        for model, compat in entries:
> > +            seq +=3D 1
> > +            with fsw.add_node(f'conf-{seq}'):
> > +                fsw.property('compatible', bytes(compat))
> > +                fsw.property_string('description', model)
> > +                fsw.property_string('fdt', f'fdt-{seq}')
> > +                fsw.property_string('kernel', 'kernel')
> > +    fsw.end_node()
> > +
> > +
> > +def compress_data(inf, compress):
> > +    """Compress data using a selected algorithm
> > +
> > +    Args:
> > +        inf (IOBase): Filename containing the data to compress
> > +        compress (str): Compression algorithm, e.g. 'gzip'
> > +
> > +    Return:
> > +        bytes: Compressed data
> > +    """
> > +    if compress =3D=3D 'none':
> > +        return inf.read()
> > +
> > +    comp =3D COMP_TOOLS.get(compress)
> > +    if not comp:
> > +        raise ValueError(f"Unknown compression algorithm '{compress}'"=
)
> > +
> > +    with tempfile.NamedTemporaryFile() as comp_fname:
> > +        with open(comp_fname.name, 'wb') as outf:
> > +            done =3D False
> > +            for tool in comp.tools.split(','):
> > +                try:
> > +                    subprocess.call([tool, '-c'], stdin=3Dinf, stdout=
=3Doutf)
> > +                    done =3D True
> > +                    break
> > +                except FileNotFoundError:
> > +                    pass
> > +            if not done:
> > +                raise ValueError(f'Missing tool(s): {comp.tools}\n')
> > +            with open(comp_fname.name, 'rb') as compf:
> > +                comp_data =3D compf.read()
> > +    return comp_data
> > +
> > +
> > +def output_dtb(fsw, seq, fname, arch, compress):
> > +    """Write out a single devicetree to the FIT
> > +
> > +    Args:
> > +        fsw (libfdt.FdtSw): Object to use for writing
> > +        seq (int): Sequence number (1 for first)
> > +        fmame (str): Filename containing the DTB
> > +        arch: FIT architecture, e.g. 'arm64'
> > +        compress (str): Compressed algorithm, e.g. 'gzip'
> > +
> > +    Returns:
> > +        tuple:
> > +            str: Model name
> > +            bytes: Compatible stringlist
> > +    """
> > +    with fsw.add_node(f'fdt-{seq}'):
> > +        # Get the compatible / model information
> > +        with open(fname, 'rb') as inf:
> > +            data =3D inf.read()
> > +        fdt =3D libfdt.FdtRo(data)
> > +        model =3D fdt.getprop(0, 'model').as_str()
> > +        compat =3D fdt.getprop(0, 'compatible')
> > +
> > +        fsw.property_string('description', model)
> > +        fsw.property_string('type', 'flat_dt')
> > +        fsw.property_string('arch', arch)
> > +        fsw.property_string('compression', compress)
> > +        fsw.property('compatible', bytes(compat))
> > +
> > +        with open(fname, 'rb') as inf:
> > +            compressed =3D compress_data(inf, compress)
> > +        fsw.property('data', compressed)
> > +    return model, compat
> > +
> > +
> > +def build_fit(args):
> > +    """Build the FIT from the provided files and arguments
> > +
> > +    Args:
> > +        args (Namespace): Program arguments
> > +
> > +    Returns:
> > +        tuple:
> > +            bytes: FIT data
> > +            int: Number of configurations generated
> > +            size: Total uncompressed size of data
> > +    """
> > +    def add_file(fname):
> > +        nonlocal seq, size
> > +
> > +        if os.path.splitext(fname)[1] =3D=3D '.dtb':
> > +            seq +=3D 1
> > +            size +=3D os.path.getsize(fname)
> > +            model, compat =3D output_dtb(fsw, seq, fname, args.arch,
> > +                                       args.compress)
> > +            entries.append([model, compat])
> > +            return True
> > +
> > +    seq =3D 0
> > +    size =3D 0
> > +    fsw =3D libfdt.FdtSw()
> > +    setup_fit(fsw, args.name)
> > +    entries =3D []
> > +
> > +    # Handle the kernel
> > +    with open(args.kernel, 'rb') as inf:
> > +        comp_data =3D compress_data(inf, args.compress)
> > +    size +=3D os.path.getsize(args.kernel)
> > +    write_kernel(fsw, comp_data, args)
> > +
> > +    for path in args.srcdir:
> > +        # Handle a list of devicetree files
> > +        if path.startswith('@'):
> > +            with open(path[1:], 'r', encoding=3D'utf-8') as inf:
> > +                for fname in inf.read().splitlines():
> > +                    add_file(fname)
>
>
>
>
> You missed the point of my suggestion.
>
>
> I did not mean the "@file" syntax
> specifically for containing the device trees.
>
>
> It is common for tools to support the "@file" syntax
> to avoid "Argument list too long" error.
>
>
>
> See "man ar", "man ld", etc. for example.
>
>
>  @file
>    Read command=E2=80=90line options from file. The options read are inse=
rted in
>    place of the original @file option. If file does not exist, or cannot
>    be read, then the option will be treated literally, and not removed.
>
>
>
>
> It must be generic enough to contain any command line parameters.
>
>
> And, you do not even implement it yourself because
> it is just a matter of adding fromfile_prefix_chars=3D'@'
>
>
> See the document.
>
>   https://docs.python.org/3/library/argparse.html#fromfile-prefix-chars


Or, if you prefer using the 'file' only for containing DTB files,
I think it is better to use a standard short/long option instead of
the @file syntax.


For example, 'tar' can take files from FILE instead of the
positional parameters of the command line.


'man tar':

  -T, --files-from=3DFILE
       Get names to extract or create from FILE.


--=20
Best Regards
Masahiro Yamada