Install with virtio disk fails due to unknown serial

[Joshua Powers]

Description:
Using the daily live server ISO (subiquity), creating a VM with virt-manager and attaching a virt-io disk results in an install failure. Based on a conversation in #curtin this is because probert is not getting a serial number and uses a default value of "Unknown serial". Subiquity needs to supply the path to curtin instead.

Subiquity log:
https://paste.ubuntu.com/26399406/

Curtin log:
https://paste.ubuntu.com/26399408/

Error message:
ValueError: no disk with serial 'Unknown_Serial' found

[Ryan Harper (raharper)]

when installing with curtin, disks can be specified via the 'path' key or 'serial'.

When specifying 'serial', curtin will attempt to locate the target disk by glob;ing in /dev/disk/by-id/*serial* to find the disk that matches the specified serial number.

In this instance, the virtio disk was not provided with a serial number, probert appears to have provided a serial number of 'Unknown_Serial' which was not found in /dev/disk/by-id/ on the install source machine.

subiquity likely needs to determine if it can use 'serial' or 'path' based on the probert information. Probert may need to omit serial value, or use a 'none' value instead of 'Unknown_Serial'.

If we're feeling lucky, we could also file a qemu bug to see if upstream is interested in having virtio disks have a default serial number like IDE devices do (as well as network devices which get a default mac address).

[Michael Hudson-Doyle (mwhudson)]

Yeah, I think it's pretty lame that virtio disks don't get a default serial. Agree we should fall back to path in this case for now.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[daftykins (dbonham-gmail)]

I also ran into this failure, however within VMware workstation 12. I created a standard VM using a SCSI disk (as is recommended) and saw installation fail instantly after the partitioner step.

Interestingly, reconfiguring the disk as "IDE" allowed installation to complete. Here is my subiquity log confirming the same lack of serial number issue:

http://termbin.com/lqk4