Right now scsi-generic is parsing the CDB, in order to compute the expected number of bytes to be transferred. This is necessary if DMA is done by the HBA via scsi_req_data, but it prevents executing vendor-specific commands via scsi-generic because we don't know how to parse them.
If DMA is delegated to the SCSI layer via get_sg_list, we know in advance how many bytes the guest will want to receive and we can pass the information straight from the guest to SG_IO. In this case, it is unnecessary to parse the CDB to get the same information. scsi-disk needs it to detect underruns and overruns, but scsi-generic and scsi-block can just ask the HBA about the transfer direction and size. This series introduces a new parse_cdb callback in both the device and the HBA. The latter is called by scsi_bus_parse_cdb, which devices can call for passthrough requests in their implementation of parse_cdb. Tamuki-san, can you please test if these patches are okay for your usecase? Paolo Paolo Bonzini (5): scsi-bus: prepare scsi_req_new for introduction of parse_cdb scsi-bus: introduce parse_cdb in SCSIDeviceClass and SCSIBusInfo scsi-block: extract scsi_block_is_passthrough scsi-block, scsi-generic: implement parse_cdb virtio-scsi: implement parse_cdb hw/scsi/scsi-bus.c | 68 ++++++++++++++++++++++++++++++++++---------------- hw/scsi/scsi-disk.c | 52 +++++++++++++++++++++++++++++--------- hw/scsi/scsi-generic.c | 7 ++++++ hw/scsi/virtio-scsi.c | 24 ++++++++++++++++++ include/hw/scsi/scsi.h | 7 ++++++ 5 files changed, 124 insertions(+), 34 deletions(-) -- 1.9.3
