linux-kernel - Re: [PATCH v1] partitions/efi: Add 'gpt

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Date:   Wed, 19 Feb 2020 17:26:57 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Davidlohr Bueso <dave@...olabs.net>,
        Colin Cross <ccross@...roid.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        David Heidelberg <david@...t.cz>,
        Peter Geis <pgwipeout@...il.com>,
        linux-efi <linux-efi@...r.kernel.org>,
        linux-tegra@...r.kernel.org, linux-block@...r.kernel.org,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] partitions/efi: Add 'gpt_sector' kernel cmdline parameter

On Wed, 19 Feb 2020 at 17:25, Dmitry Osipenko <digetx@...il.com> wrote:
>
> The gpt_sector=<sector> causes the GPT partition search to look at the
> specified sector for a valid GPT header if the GPT is not found at the
> beginning or the end of block device.
>
> In particular this is needed for NVIDIA Tegra consumer-grade Android
> devices in order to make them usable with the upstream kernel because
> these devices use a proprietary / closed-source partition table format
> for the EMMC and it's impossible to change the partition's format. Luckily
> there is a GPT table in addition to the proprietary table, which is placed
> in uncommon location of the EMMC storage and bootloader passes the
> location to kernel using "gpt gpt_sector=<sector>" cmdline parameters.
>
> This patch is based on the original work done by Colin Cross for the
> downstream Android kernel.
>
> Cc: Colin Cross <ccross@...roid.com>
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>

Which block device is this parameter applied to?

> ---
>  Documentation/admin-guide/kernel-parameters.txt |  5 +++++
>  block/partitions/efi.c                          | 15 +++++++++++++++
>  2 files changed, 20 insertions(+)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 50138e6826a1..ee4781daa379 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1382,6 +1382,11 @@
>                         primary GPT is corrupted, it enables the backup/alternate
>                         GPT to be used instead.
>
> +       gpt_sector      [EFI] Forces GPT partition search to look at the
> +                       specified sector for a valid GPT header if the GPT is
> +                       not found at the beginning or the end of the block
> +                       device.
> +
>         grcan.enable0=  [HW] Configuration of physical interface 0. Determines
>                         the "Enable 0" bit of the configuration register.
>                         Format: 0 | 1
> diff --git a/block/partitions/efi.c b/block/partitions/efi.c
> index db2fef7dfc47..0c8926d76d7a 100644
> --- a/block/partitions/efi.c
> +++ b/block/partitions/efi.c
> @@ -103,6 +103,17 @@ force_gpt_fn(char *str)
>  }
>  __setup("gpt", force_gpt_fn);
>
> +/* This allows a kernel command line option 'gpt_sector=<sector>' to
> + * enable GPT header lookup at a non-standard location.
> + */
> +static u64 force_gpt_sector;
> +static int __init
> +force_gpt_sector_fn(char *str)
> +{
> +       WARN_ON(kstrtoull(str, 10, &force_gpt_sector) < 0);
> +       return 1;
> +}
> +__setup("gpt_sector=", force_gpt_sector_fn);
>
>  /**
>   * efi_crc32() - EFI version of crc32 function
> @@ -621,6 +632,10 @@ static int find_valid_gpt(struct parsed_partitions *state, gpt_header **gpt,
>          if (!good_agpt && force_gpt)
>                  good_agpt = is_gpt_valid(state, lastlba, &agpt, &aptes);
>
> +       if (!good_agpt && force_gpt && force_gpt_sector)
> +               good_agpt = is_gpt_valid(state, force_gpt_sector,
> +                                        &agpt, &aptes);
> +
>          /* The obviously unsuccessful case */
>          if (!good_pgpt && !good_agpt)
>                  goto fail;
> --
> 2.24.0
>