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

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Message-ID: <9c7343eb-1b09-ffcf-cba0-11d6a26dfd77@gmail.com>
Date:   Mon, 24 Feb 2020 20:23:54 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Karel Zak <kzak@...hat.com>, Stephen Warren <swarren@...dotorg.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        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@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-block@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] partitions/efi: Add 'gpt_sector' kernel cmdline
 parameter

24.02.2020 19:33, Karel Zak пишет:
> On Wed, Feb 19, 2020 at 09:59:54AM -0700, Stephen Warren wrote:
>> On 2/19/20 9:27 AM, Christoph Hellwig wrote:
>>> On Wed, Feb 19, 2020 at 07:23:39PM +0300, Dmitry Osipenko 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.
>>>
>>> I don't think a magic command line is the way to go.  The best would be
>>> to reverse-engineer the proprietary partition table format.  If that is
>>> too hard we can at least key off the odd GPT location based of it's
>>> magic number.
> 
>  +1
> 
>> I thought that the backup GPT was always present in the standard location;
> 
> If they have proprietary stuff on begin of the device and valid backup
> GPT at the end of the device then designer of this junk is crazy, because
> many GPT fdisk-like tools will try to recover from the backup header and 
> overwrite the unknown (invalid) stuff at the begin of the device...

It's a problem created by vendor, but these devices are assumed to run
Android-only. So it's not really that bad :)