From: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>

During SCSI bus enumeration A/UX sends a MODE SENSE command to the CDROM with
the DBD bit unset and expects the response to include a block descriptor. As per
the latest SCSI documentation, QEMU currently force-disables the block
descriptor for CDROM devices but the A/UX driver expects the requested block
descriptor to be returned.

If the block descriptor is not returned in the response then A/UX becomes
confused, since the block descriptor returned in the MODE SENSE response is
used to generate a subsequent MODE SELECT command which is then invalid.

Add a new SCSI_DISK_QUIRK_MODE_SENSE_ROM_USE_DBD quirk to allow this behaviour
to be enabled as required. Note that an additional workaround is required for
the previous SCSI_DISK_QUIRK_MODE_PAGE_APPLE_VENDOR quirk which must never
return a block descriptor even though the DBD bit is left unset.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Message-Id: <20220622105314.802852-5-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/scsi/scsi-disk.c    | 27 +++++++++++++++++++++++----
 include/hw/scsi/scsi.h |  1 +
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
index 2672730eca..b1d08bfba5 100644
--- a/hw/scsi/scsi-disk.c
+++ b/hw/scsi/scsi-disk.c
@@ -1279,10 +1279,27 @@ static int scsi_disk_emulate_mode_sense(SCSIDiskReq *r, uint8_t *outbuf)
             dev_specific_param |= 0x80; /* Readonly.  */
         }
     } else {
-        /* MMC prescribes that CD/DVD drives have no block descriptors,
-         * and defines no device-specific parameter.  */
-        dev_specific_param = 0x00;
-        dbd = true;
+        if (s->quirks & (1 << SCSI_DISK_QUIRK_MODE_SENSE_ROM_USE_DBD)) {
+            /* Use DBD from the request... */
+            dev_specific_param = 0x00;
+
+            /*
+             * ... unless we receive a request for MODE_PAGE_APPLE_VENDOR
+             * which should never return a block descriptor even though DBD is
+             * not set, otherwise CDROM detection fails in MacOS
+             */
+            if (s->quirks & (1 << SCSI_DISK_QUIRK_MODE_PAGE_APPLE_VENDOR) &&
+                page == MODE_PAGE_APPLE_VENDOR) {
+                dbd = true;
+            }
+        } else {
+            /*
+             * MMC prescribes that CD/DVD drives have no block descriptors,
+             * and defines no device-specific parameter.
+             */
+            dev_specific_param = 0x00;
+            dbd = true;
+        }
     }
 
     if (r->req.cmd.buf[0] == MODE_SENSE) {
@@ -3102,6 +3119,8 @@ static Property scsi_cd_properties[] = {
                       5),
     DEFINE_PROP_BIT("quirk_mode_page_apple_vendor", SCSIDiskState, quirks,
                     SCSI_DISK_QUIRK_MODE_PAGE_APPLE_VENDOR, 0),
+    DEFINE_PROP_BIT("quirk_mode_sense_rom_use_dbd", SCSIDiskState, quirks,
+                    SCSI_DISK_QUIRK_MODE_SENSE_ROM_USE_DBD, 0),
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/include/hw/scsi/scsi.h b/include/hw/scsi/scsi.h
index e090ea1b40..845d05722b 100644
--- a/include/hw/scsi/scsi.h
+++ b/include/hw/scsi/scsi.h
@@ -228,5 +228,6 @@ extern const SCSIReqOps scsi_generic_req_ops;
 
 /* scsi-disk.c */
 #define SCSI_DISK_QUIRK_MODE_PAGE_APPLE_VENDOR             0
+#define SCSI_DISK_QUIRK_MODE_SENSE_ROM_USE_DBD             1
 
 #endif
-- 
2.36.1