linux-ext4 - [Bug 216714] Issue with file system image created with mke2fs parameter -E offset

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Message-ID: <bug-216714-13602-noe4b8eF4L@https.bugzilla.kernel.org/>
Date:   Mon, 21 Nov 2022 08:56:40 +0000
From:   bugzilla-daemon@...nel.org
To:     linux-ext4@...r.kernel.org
Subject: [Bug 216714] Issue with file system image created with mke2fs
 parameter -E offset

https://bugzilla.kernel.org/show_bug.cgi?id=216714

Lukas Czerner (lczerner@...hat.com) changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |lczerner@...hat.com

--- Comment #1 from Lukas Czerner (lczerner@...hat.com) ---
Hi,

the -E offset=10 creates a file system that is offset by 10 bytes from the
beginning of the device or a file (as is written in the man page). It is no
wonder then that the tools can't recognize the file system on the device or a
file because the super block is not where it should be - it is offset by 10
bytes.

If you want to use such a file system you have to present it to the other
tools, or even kernel, with the correct offset. It is not going to be
automatic.

So for example this works:

mke2fs -q -t ext4 -E offset=10 image 500M
sudo losetup -o 10 --show -f image
/dev/loop0
sudo e2fsck -f /dev/loop0
e2fsck 1.46.6-rc1 (12-Sep-2022)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/loop0: 11/128016 files (0.0% non-contiguous), 26684/512000 blocks

I hope it helps.

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