Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v1] partitions/efi: Add 'gpt_sector' kernel cmdline
 parameter
To:     Karel Zak <kzak@redhat.com>, Stephen Warren <swarren@wwwdotorg.org>
Cc:     Christoph Hellwig <hch@infradead.org>,
        Jens Axboe <axboe@kernel.dk>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Colin Cross <ccross@android.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= <mirq-linux@rere.qmqm.pl>,
        David Heidelberg <david@ixit.cz>,
        Peter Geis <pgwipeout@gmail.com>, linux-efi@vger.kernel.org,
        linux-tegra@vger.kernel.org, linux-block@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20200219162339.16192-1-digetx@gmail.com>
 <20200219162738.GA10644@infradead.org>
 <f9e41108-7811-0deb-6977-be0f60e23b52@wwwdotorg.org>
 <20200224163342.d4acf224b56celup@ws.net.home>
From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <9c7343eb-1b09-ffcf-cba0-11d6a26dfd77@gmail.com>
Date:   Mon, 24 Feb 2020 20:23:54 +0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.3.0
MIME-Version: 1.0
In-Reply-To: <20200224163342.d4acf224b56celup@ws.net.home>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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 :)