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

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Message-ID: <bug-216714-13602-UHEoF1jjyZ@https.bugzilla.kernel.org/>
Date:   Mon, 28 Nov 2022 15:51:17 +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

Theodore Tso (tytso@....edu) changed:

           What    |Removed                     |Added
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                 CC|                            |tytso@....edu

--- Comment #4 from Theodore Tso (tytso@....edu) ---
I'm curious --- *why* are you wanting to create file systems with an offset to
begin with?    The original reason why this feature was added was in a highly
specialized case where someone was creating a system image for some embedded
system or for a virtual machine.  In this use case, the image contained a
partition table, and the offset feature was used to create a filesystem at the
appropriate location as specified by the partition table.

A typical use case is as part of an automated build procedure where the system
image (say, for an Android mobile device, or some ARM development board, such
as a Beaglebone, Arduino, etc., or some Virtual machine), using the mke2fs -d
option to pre-populate the file system with the root file system, or some data
partition, etc.   Since Best Practices for such automated build systems involve
creating a reproducible build, there is nothing precious on the file system
that can't be replicated by re-running the the automated build.   So if the
offset is wrong (which is to say, inconsistent with the partition table which
was laid down using the same automated build system), the developer will just
curse to themselves, and can determine the offset by looking at the build image
creation script, and then adjust that offset to match with the offset that was
set in the partition table.

So I'm a bit perplexed about why you were using a random starting offset for
the file system, and why you can't seem to figure out the offset afterwards. 
The typical approach is to RTFS (Read The Fine Shellscript) to determine the
offset, and then to fix the perhaps not-so-fine shell script.  :-)

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