Re: [Xen-devel] [PATCH v6] libxl: allow 'phy' backend to use empty files

["Alex Braunegg" <alex.braunegg@xxxxxxxxx>]

Hi George,

> I take it that if he used a phy backend for a cdrom, that "xl cd-eject" 
> failed?

No - I was always using ISO images for cd-rom devices. In the 4.4 configuration 
I was specifying it as a file.

In Xen 4.4 and 4.6 (before patching) whenever I attempted to perform an 'xl 
cd-eject' it always failed. I didn’t perform the triage of what commit broke 
the functionality - so I cant advise on if this is what broke it.

A sample of the configurations of what I used is below:

================

        # Xen 4.4
        builder='hvm'
        memory = 512
        name = 'CentOS_Test'
        disk = [ 
'phy:/dev/zvol/storage/xen/CentOS_Test/disk_sda,hda,w','file:/storage/samba/xeniso/CentOS-6.5-x86_64-minimal.iso,hdc:cdrom,r'
 ]
        # boot on floppy (a), hard disk (c) or CD-ROM (d)
        # default: hard disk, cd-rom, floppy
        boot='cd'


        # Xen 4.6
        builder='hvm'
        memory = 512
        name = 'CentOS_Test'
        disk = [ 
'/dev/zvol/storage/xen/CentOS_Test/disk_sda,,hda','/storage/samba/xeniso/CentOS-6.5-x86_64-minimal.iso,,hdc,cdrom'
 ]
        # boot on floppy (a), hard disk (c) or CD-ROM (d)
        # default: hard disk, cd-rom, floppy
        boot='cd'

================

After patching Xen 4.6, I can now perform the xl cd-eject and load an alternate 
ISO into the VM without issue. However if I just want to eject the ISO as per 
what you would normally do on a physical system after install, I have to 
'eject' but then insert a 'dummy' ISO file to keep the cd-rom device available 
to the VM through reboots / shutdowns:

        disk = [ 
'/dev/zvol/storage/xen/CentOS_Test/disk_sda,,hda','/storage/samba/xeniso/dummy.iso,,hdc,cdrom'
 ]

Without having some sort of valid 'dummy' ISO file that contains nothing, Xen 
has issues about creating the cd-rom device on creation and reboots, and 
certainly in the VM no cd-rom device is then available - meaning down the track 
if I want to load an ISO I cannot easily 'insert' another ISO file without 
powering off the VM, making the configuration change and powering the VM back 
on again.

It would be nice at some point to have the configuration where the cd-rom drive 
can presented to the VM without having a valid ISO / file loaded - which would 
then operate as per physical devices - cd-rom devices show up, but drive 
contents are empty:

        disk = [ 
'/dev/zvol/storage/xen/CentOS_Test/disk_sda,,hda',',,hdc,cdrom' ]

Best regards,

Alex



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