Greetings Peter, > Sent: Monday, November 02, 2020 at 4:20 PM > From: "Peter Krempa" <pkrempa@xxxxxxxxxx> > To: "daggs" <daggs@xxxxxxx> > Cc: libvirt-users@xxxxxxxxxx > Subject: Re: proper config for qemu's host_cdrom > > Note that all of the above is not "SCSI passthrough" but rather device > emulation backed with a real cdrom. This is fine if you want to use the > cdrom for block operations (reading) CDs. > > In that case qemu must use "host_cdrom" to provide functionality such as > eject. > > For true SCSI passtrhrough, when all commands are passed to the host > device (good also for other operations, e.g. writing CDs) > > For such operation the XML using <hostdev> ... > > ... as you've shown here is used. > > In such case we use 'host_device' even for cdroms. qemu only allows to > use the 'host_device' protocol backend. > > The main difference is that for the emulation interface (<disk>) we use > the block interface for the cdrom (/dev/sr0 for example). For hostdev we > open the SCSI-generic interface which is a character device and is used > to pass generic commads (/dev/sg0) > > I've originally attempted to change the way we open /dev/sg0 as you > might know since you were CC'd on that thread, but testing actually > proved that the above approach is correct, for scsi passthrough we don't > need to treat the cdrom differently. > > so host_device is the right way in this case? if so, any issues I see in the vm should be sent to qemu ml right? Dagg,
