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Re: [Qemu-block] qemu-img: add seek option to dd


From: Richard W.M. Jones
Subject: Re: [Qemu-block] qemu-img: add seek option to dd
Date: Wed, 20 Feb 2019 05:54:25 +0000
User-agent: Mutt/1.5.21 (2010-09-15)

It seems like it's not easy to write to a place in a qcow2 file using
qemu-io or qemu-img.  For example suppose I want to overwrite blocks
100 and 101 with my own data:

$ qemu-img dd -f raw -O qcow2 bs=4096 skip=100 count=2 \
              if=/tmp/input.raw of=/tmp/disk.qcow2
qemu-img: /tmp/input.raw: cannot skip to specified offset

Skip is skipping the input, not the output.  Turning to qemu-io, it
doesn't look like you can control the data written (only write
patterns).

This patch looks good, but AFAICT it never went upstream:

  https://patchwork.kernel.org/patch/9273161/
  "qemu-img: add seek option to dd"

Is there anything I'm missing?  What is the status of that patch?

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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