linux-kernel - Re: [PATCH] partitions/efi: treat size mismatch as a warning, not an error

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Message-ID: <CAD=FV=WKp-QYZf+t8fk_iYw3rDtZz7=Neg=S8pwPw_=e-4AnKQ@mail.gmail.com>
Date:	Fri, 11 Oct 2013 08:53:57 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Karel Zak <kzak@...hat.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>,
	Matt Fleming <matt.fleming@...el.com>,
	Sean Paul <seanpaul@...omium.org>,
	Olof Johansson <olof@...om.net>,
	Bill Richardson <wfrichar@...omium.org>,
	Josh Triplett <josh@...htriplett.org>,
	Davidlohr Bueso <davidlohr@...com>
Subject: Re: [PATCH] partitions/efi: treat size mismatch as a warning, not an error

Karel,

On Fri, Oct 11, 2013 at 2:51 AM, Karel Zak <kzak@...hat.com> wrote:
> On Thu, Oct 10, 2013 at 04:28:22PM -0700, Doug Anderson wrote:
>> +      *
>> +      * Consider a bad value here to be a warning to support dd-ing
>> +      * an image from a smaller disk to a bigger disk.
>>        */
>>       if (ret == GPT_MBR_PROTECTIVE) {
>>               sz = le32_to_cpu(mbr->partition_record[part].size_in_lba);
>>               if (sz != (uint32_t) total_sectors - 1 && sz != 0xFFFFFFFF)
>> -                     ret = 0;
>> +                     pr_warn("%s: mbr size mismatch (%u != %u)\n", __func__,
>> +                             sz, (uint32_t)((uint32_t) total_sectors - 1));
>>       }
>
>  I did the same change to util-linux v2.24 fdisk, so you can use the fdisk
>  to update your protective MBR and boot without warnings.

Yup, I think we've come up with a number of ways that we can update
the partition table to avoid the problems.  :)  ...but the "feature"
that used to work was being able to dd an image from a smaller disk
onto a larger disk and have it "just boot" (though perhaps with some
warning messages).  This feature was used in the Chrome OS workflow to
create bootable USB sticks / SD cards.  We certainly could say that
what the Chrome OS workflow is doing is illegal / bad / unethical, but
it has been working for years and it would be nice for it to keep
working if possible.  :)

http://xkcd.com/1172/

-Doug
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