[libvirt-users] mkfs fails on qemu-nbd device

Hi All, I am unable to figure out the issue here, when I try to create a filesystem (ext4) on a virtual disk using qemu-nbd. This happens intermittently. Following is the sequence of commands:- $> qemu-img create -f qcow2 test.qcow2 30G $> qemu-nbd --connect=/dev/nbd0 test.qcow2 $> *mkfs.ext4 /dev/nbd0* * mkfs.ext4: Device size reported to be zero. Invalid partition specified, or* *Thu Jun 13 14:44:24 2019 partition table wasn't reread after running fdisk, due to* *Thu Jun 13 14:44:24 2019 a modified partition being busy and in use. You may need to reboot* *Thu Jun 13 14:44:24 2019 to re-read your partition table.* Following is the version details: root@localhost:~# qemu-img --version qemu-img version 2.8.1(Debian 1:2.8+dfsg-6+deb9u7) Copyright (c) 2003-2016 Fabrice Bellard and the QEMU Project developers root@localhost:~# qemu-nbd --version qemu-nbd version 0.0.1 Written by Anthony Liguori. Copyright (C) 2006 Anthony Liguori <anthony(a)codemonkey.ws&gt;. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. root@localhost:~# uname -a Linux localhost 4.9.0-9-amd64 #1 SMP Debian 4.9.168-1+deb9u2 (2019-05-13) x86_64 GNU/Linux Regards Tanmoy Sinha