Re: [PATCH v2 1/3] libxl: Create empty file for Phy cdrom

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Thu, Feb 01, 2024 at 04:40:02PM -0500, Jason Andryuk wrote:
> With a device model stubdom, dom0 exports a PV disk to the stubdom.
> Inside the stubdom, QEMU emulates a cdrom to the guest with a
> host_device pointing at the PV frontend (/dev/xvdc)
> 
> An empty cdrom drive causes problems booting the stubdom.  The PV disk
> protocol isn't designed to support no media.  That can be partially
> hacked around, but the stubdom kernel waits for all block devices to
> transition to Connected.  Since the backend never connects empty media,
> stubdom launch times out and it is destroyed.
> 
> Empty media and the PV disks not connecting is fine at runtime since the
> stubdom keeps running irrespective of the disk state.
> 
> Empty media can be worked around my providing an empty file to the
> stubdom for the PV disk source.  This works as the disk is exposed as a
> zero-size disk.  Dynamically create the empty file as needed and remove
> in the stubdom cleanup.
> 
> libxl__device_disk_set_backend() needs to allow through these "empty"
> disks with a pdev_path.
> 
> Fixup the params writing since scripts have trouble with an empty params
> field.
> 
> This works for non-stubdom HVMs as well.
> 
> Signed-off-by: Jason Andryuk <jandryuk@xxxxxxxxx>

Reviewed-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>

Thanks,

-- 
Anthony PERARD