Bug 2140537

Summary: [RFE] dm-thin: allow supplying an offset to the table
Product: [Community] LVM and device-mapper Reporter: Demi Marie Obenour <demiobenour>
Component: device-mapperAssignee: Mikuláš Patočka <mpatocka>
Status: NEW --- QA Contact: cluster-qe <cluster-qe>
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: unspecifiedCC: agk, heinzm, jbrassow, msnitzer, prajnoha, thornber, zkabelac
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Hardware: All   
OS: Linux   
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Description Demi Marie Obenour 2022-11-07 05:26:30 UTC
Description of problem:
Unlike the linear and crypt targets, the thin target does not take an offset.

Version-Release number of selected component (if applicable):
6.0.7

How reproducible:
100%

Steps to Reproduce:
Try to overwrite the first part of a device (a partition table, say) with the following table

> 0 1 linear somedevice 0
> 1 100 thin 0 somepool / 1

Actual results:
There is no way to do this without a separate linear layer, which hurts performance.

Expected results:
It is possible.

Additional info:
“/” is used as a placeholder to indicate “no external origin device”.

Comment 1 Zdenek Kabelac 2023-02-07 16:35:17 UTC
Related to proposed patch: https://listman.redhat.com/archives/dm-devel/2023-February/053187.html
and developer's  NACK:  https://listman.redhat.com/archives/dm-devel/2023-February/053197.html

we really can't be adding 'linear' capabilities to every target.

Focus should go to optimize performance drop introduced by using 'extra' dm-layer on top of thin device.

Passing to Mikulas to consider what we can the to improve dm core logic here.