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Re: btrfs trim erases bootloader area


From: Filipe Manana
Subject: Re: btrfs trim erases bootloader area
Date: Thu, 7 Jan 2016 23:10:28 +0000

On Thu, Jan 7, 2016 at 10:05 PM, Chris Murphy <address@hidden> wrote:
> On Thu, Jan 7, 2016 at 12:16 PM, Filipe Manana <address@hidden> wrote:
>> On Thu, Jan 7, 2016 at 7:11 PM, Andrei Borzenkov <address@hidden> wrote:
>>> As discussed on opensuse-factory list, running fstrim on btrfs erases
>>> bootloader area, rendering system unbootable. See
>>>
>>> https://lists.opensuse.org/opensuse-factory/2016-01/msg00067.html
>>> https://lists.opensuse.org/opensuse-factory/2016-01/msg00090.html
>>>
>>> and follow-ups that demonstrate that beginning of device gets zeroed out.
>>>
>>> Not sure what we can do, but from GRUB side I can only see disabling
>>> embedding support on btrfs entirely.
>>
>> Try this (sent to the btrfs mailing list yesterday):
>>
>> http://git.kernel.org/cgit/linux/kernel/git/fdmanana/linux.git/commit/?h=integration-4.5&id=7b6cb6618b45bb383f9336ec89df5f1f31f9935b
>>
>> thanks
>
> The description is a bit confusing by referring to MBR, which mainly
> exists only at LBA 0. In the case of extended partitions, the EBR
> (using the same MBR format) is still outside the LBA range for Btrfs
> to apply fitrim ioctl. The VBR however, would be inside that range,
> and it's that 64KiB bootloader pad Btrfs reserves that's being
> inadvertently obliterated. Correct?

Right, the title and description is confusing. I lacked the
terminology and all technical details of grub, so I just used MBR to
refer to any sector containing code used by the boot loader.
Do you like the following title/change log better?

http://git.kernel.org/cgit/linux/kernel/git/fdmanana/linux.git/commit/?h=integration-4.5&id=6a340b36b68463ddca2b088c398d94a067a00e82

I'll resend it later or tomorrow.

thanks

>
>
>
> Chris Murphy



-- 
Filipe David Manana,

"Reasonable men adapt themselves to the world.
 Unreasonable men adapt the world to themselves.
 That's why all progress depends on unreasonable men."



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