[Qemu-discuss] Permission denied when using block-dirty-bitmap on dynamically-mounted backup drive.

[Mike Lee]

I am using Qemu's block-dirty-bitmap features to perform full/incremental
backups of my qcow2 images.  Things are working great but when I go to
perform the initial full backup command to create the bitmap I get
"libvirt-49 Could not create file: Permission denied".  I'm issuing these
json-based commands to the qemu monitor via the virsh qemu-monitor-command
command.  Yes, the dest. dir is owned by libvirt-qemu.kvm user/group.

The only time I get this permission error is when I'm trying to write
backup qcow2 files to a dynamically-mounted external drive (USB, etc.).  If
I create a manual mount point for it and provide an entry in my fstab file,
things work great.

Any idea how I can do backups to destination disks that are auto-mounted
(mounted automatically when I plug-in the external USB disk?

The command I'm running is:

virsh qemu-monitor-command ubuntu16.04 --pretty \
'{"execute":
"transaction",' \
'    "arguments":' \
'    {' \
'        "actions":' \
'        [' \
'            {"type": "block-dirty-bitmap-add",' \
'             "data": {"node": "drive-virtio-disk1", "name": "bitmap0"}' \
'            },' \
'            {"type": "drive-backup",' \
'             "data": {"device": "drive-virtio-disk1",' \
'                      "target":
"/media/mike/Seagate2TB/backups/qemu/ubuntu16.04/2014-09-24/ubuntu16.04_full_backup_2017-09-24.qcow2",'
\
'                      "sync": "full", "format": "qcow2"' \
'                     }' \
'            }' \
'        ]' \
'    }' \
'}'

Thanks.


Mike