linux-ext4 - Re: Modification of block device by R/O mount

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Message-ID: <bdf2626f-580a-4af2-9fb0-5e3ebe944f95@spornkuller.de>
Date: Thu, 1 Aug 2024 08:18:23 +0200
From: Johannes Bauer <canjzymsaxyt@...rnkuller.de>
To: Dave Chinner <david@...morbit.com>
Cc: linux-ext4@...r.kernel.org
Subject: Re: Modification of block device by R/O mount

Hey Dave,

thanks for your response!

Am 01.08.24 um 03:53 schrieb Dave Chinner:

>> Is there a way to mitigate it?
> 
> If you want to stop the filesystem writing to the block device, you
> have to set the -block device- to be read only. At this point, the
> filesystem will refuse to mount if it needs to write to the block
> device during mount.

But my point is, that is what I am doing -- creating the losetup mapping 
R/O:

# losetup --read-only --show -f image.img
/dev/loop35

# echo foo >/dev/loop35
bash: echo: write error: Operation not permitted

I.e., the block device is write protected and *yet* it changes content. 
This is what I find so extremely puzzling, that the file system should 
not have the capability to change the underlying block device, yet it does.

Cheers,
Johannes

-- 
"A PC without Windows is like a chocolate cake without mustard."