On Mon, Mar 10, 2025 at 09:13:11 +0000, Daniel P. Berrangé wrote:
On Mon, Mar 10, 2025 at 10:10:53AM +0100, Peter Krempa wrote:
On Mon, Mar 10, 2025 at 09:05:28 +0000, Daniel P. Berrangé wrote:
On Sat, Mar 08, 2025 at 02:57:41PM +0900, Akihiko Odaki wrote:
usb-storage is a compound device that automatically creates a USB mass storage device and a SCSI device as its backend. Unfortunately it lacks some configuration options that are usually present with a SCSI device, and cannot represent CD-ROM in particular.
Replace usb-storage with usb-bot, which can be combined with a manually created SCSI device. libvirt will configure the SCSI device in a way identical with how QEMU does for usb-storage except that now it respects a configuration option to represent CD-ROM.
Is this change compatible for QEMU's VMState aka migration ABI compatible ?
Based on my tests so far it seems compatible in terms of VMstate and also guest ABI at least to the first glance (lsusb, lsscsi -v etc) seems identical at least for the default 'read-write'/non-cdrom disk.
I didn't yet test migrating with a cdrom to an older daemon though, which based on the above paragraph should have guest-visible difference.
Any such configuratin of the latter is arguably a bug though ? It was never presenting a cdrom, and that we allowed it was just a sign of missing XML validation surely ?
Yes that could be the case. Although it is possible that it's even a regression from switching to blockdev as I've seen claims that usb cdrom did behave correctly at that point; but I didn't care to validate that for myself given how long ago it was that we switched to blockdev.