scsi-block: always use SG_IO for MMC devices CD burning messes up the state of the host page cache and host block device. Just pass all operations down to the device, even though that might have slightly worse performance. Everything else just is not reliable in combination with burning. Reported-by: Thomas Schmitt <scdbackup@gmx.net> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>