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Re: grubenv on md, Btrfs, LUKS, etc

From: Chris Murphy
Subject: Re: grubenv on md, Btrfs, LUKS, etc
Date: Tue, 18 Sep 2018 13:40:06 -0600

On Mon, Sep 17, 2018 at 10:59 PM, Chris Murphy <address@hidden> wrote:
> Hi,
> GRUB code can certainly read files that are on Btrfs, md devices,
> LUKS, LVM, and so on. But GRUB code can also write to the physical
> block for grubenv - but are there safe guards that prevent it from
> doing so if grubenv is on something like Btrfs, mdadm raid5, LUKS?
> And also what about XFS? This used to be safe, but now with reflink
> support, grubenv could be reflink copied, meaning any overwrite is
> disallowed and must be COW'd. How is that handled?
> I'm pretty sure on Btrfs GRUB knows is can't write to grubenv, I'm
> just curious about the other cases.

OK so it allows me to create a grubenv on Btrfs without any complaint.
Will the bootloader actually try to write to this if grub.cfg contains

$ sudo grub2-editenv --verbose grubenv create
[sudo] password for chris:
address@hidden ~]$ ll
-rw-r--r--. 1 root  root     1024 Sep 18 13:37 grubenv
address@hidden ~]$ stat -f grubenv
  File: "grubenv"
    ID: ac9ba8ecdce5b017 Namelen: 255     Type: btrfs
Block size: 4096       Fundamental block size: 4096
Blocks: Total: 46661632   Free: 37479747   Available: 37422535
Inodes: Total: 0          Free: 0
address@hidden ~]$

Chris Murphy

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