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The bug is also reproduced on qemu-kvm-rhev-2.6.0-27.el7.x86_64.
+++ This bug was initially created as a clone of Bug #1379929 +++
Description of problem:
As subject
Version-Release number of selected component (if applicable):
nbdkit-1.1.12-1.fc25.x86_64
qemu-img-2.7.0-1.fc26.x86_64
How reproducible:
100%
Steps to Reproduce:
1. Create a qcow2 image:
# qemu-img create /tmp/xx.qcow2 -f qcow2 100M
Formatting '/tmp/xx.qcow2', fmt=qcow2 size=104857600 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
Export by qemu-nbd:
# qemu-nbd -t -p 30001 --format=qcow2 /tmp/xx.qcow2
2. Check the image local and via nbd
# qemu-img info /tmp/xx.qcow2
image: /tmp/xx.qcow2
file format: qcow2
virtual size: 100M (104857600 bytes)
disk size: 196K
cluster_size: 65536
Format specific information:
compat: 1.1
lazy refcounts: false
refcount bits: 16
corrupt: false
# qemu-img info nbd://localhost:30001
image: nbd://localhost:30001
file format: raw
virtual size: 100M (104857600 bytes)
disk size: unavailable
Actual results:
As step2
Expected results:
qemu-img info via nbd get right result.
Additional info:
Try to do above steps with nbdkit and the result is right.
# nbdkit -p 30000 file file=/tmp/xx.qcow2
# qemu-img info nbd://localhost:30000
image: nbd://localhost:30000
file format: qcow2
virtual size: 100M (104857600 bytes)
disk size: unavailable
cluster_size: 65536
Format specific information:
compat: 1.1
lazy refcounts: false
refcount bits: 16
corrupt: false
When you ran 'qemu-nbd' you gave it a --format=qcow2 argument, so it is exporting the *contents* of the qcow2 image, ie a *raw* volume. So the qemu-img info command is correct in reporting that it is raw.
(In reply to Daniel Berrange from comment #2)
> When you ran 'qemu-nbd' you gave it a --format=qcow2 argument, so it is
> exporting the *contents* of the qcow2 image, ie a *raw* volume. So the
> qemu-img info command is correct in reporting that it is raw.
I try to use 'qemu-nbd -t -p 30001 --format=raw' and get qcow2 format when using qemu-img info. Well, for the issue in comment0, it is not a bug.
But the manual of qemu-nbd is confusing:
-f, --format=fmt
Force the use of the block driver for format fmt instead of auto-detecting
I couldn't get the info of 'exporting the *contents* of the qcow2 image'. Maybe we should improve the manual page and give some examples.