Because opcode 0xA1 has a different meaning for CDROM/MMC devices. On such devices 0xA1 means BLANK, so it would collide if QEMU some day adds support for re-writeable mmc device.
On Wed, Aug 1, 2012 at 6:45 PM, Paolo Bonzini <pbonz...@redhat.com> wrote: > Il 01/08/2012 10:43, Cong Meng ha scritto: >>> >>> Please make this conditional on the type _not_ being TYPE_ROM. >> >> May I ask why cdrom device should be an exception? > > Because CD-ROM devices do not support ATA PASSTHROUGH (the SAT standard > only describes direct access devices---type=0x00). The 0xa1 command is > "BLANK" for CD-ROMs. > > Paolo >