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Verify the bug with below builds:
nbdkit-1.28.2-1.el9.x86_64
qemu-img-6.1.0-7.el9.x86_64
Steps:
1. Check the man page of nbdkit-cow-filter about qemu-img
# man nbdkit-cow-filter |grep qemu-img
Creating a diff with qemu-img
qemu-img(1). nbdkit must remain continuously running during the whole operation, otherwise all changes will be lost.
Run these "qemu-img" commands to construct a qcow2 file containing the differences:
qemu-img create -F raw -b nbd:localhost -f qcow2 diff.qcow2
qemu-img rebase -F raw -b disk.img -f qcow2 diff.qcow2
nbdkit-filter(3), nbdcopy(1), qemu-img(1).
2 Check if qemu-img command of nbdkit-cow-filter man page works
# nbdkit -p 10810 memory 1G
# qemu-img create -F raw -b nbd://localhost:10810 -f qcow2 diff.qcow2
Formatting 'diff.qcow2', fmt=qcow2 cluster_size=65536 extended_l2=off compression_type=zlib size=1073741824 backing_file=nbd://localhost:10810 backing_fmt=raw lazy_refcounts=off refcount_bits=16
# qemu-img rebase -F raw -b esx7.0-rhel8.5-x86_64-sda -f qcow2 diff.qcow2
# qemu-img info esx7.0-rhel8.5-x86_64-sda
image: esx7.0-rhel8.5-x86_64-sda
file format: raw
virtual size: 12 GiB (12884901888 bytes)
disk size: 1.99 GiB
# qemu-img info diff.qcow2
image: diff.qcow2
file format: qcow2
virtual size: 1 GiB (1073741824 bytes)
disk size: 177 MiB
cluster_size: 65536
backing file: esx7.0-rhel8.5-x86_64-sda
backing file format: raw
Format specific information:
compat: 1.1
compression type: zlib
lazy refcounts: false
refcount bits: 16
corrupt: false
extended l2: false
Result:
The qemu-img commands are correct in nbdkit-cow-filter man page, move the bug from ON_QA to VERIFIED
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory (new packages: nbdkit), and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHEA-2022:2408