[PATCH v2 07/11] scsi-disk: allow truncated MODE SELECT requests

[Mark Cave-Ayland]

When A/UX configures the CDROM device it sends a truncated MODE SELECT request
for page 1 (MODE_PAGE_R_W_ERROR) which is only 6 bytes in length rather than
10. This seems to be due to bug in Apple's code which calculates the CDB message
length incorrectly.

According to [1] this truncated request is accepted on real hardware whereas in
QEMU it generates an INVALID_PARAM_LEN sense code which causes A/UX to get stuck
in a loop retrying the command in an attempt to succeed.

Alter the mode page request length check so that truncated requests are allowed
as per real hardware, adding a trace event to enable the condition to be 
detected.

[1] 
https://68kmla.org/bb/index.php?threads/scsi2sd-project-anyone-interested.29040/page-7#post-316444

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
---
 hw/scsi/scsi-disk.c  | 2 +-
 hw/scsi/trace-events | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
index 71fdf132c1..c657e4f5da 100644
--- a/hw/scsi/scsi-disk.c
+++ b/hw/scsi/scsi-disk.c
@@ -1525,7 +1525,7 @@ static int mode_select_pages(SCSIDiskReq *r, uint8_t *p, 
int len, bool change)
             goto invalid_param;
         }
         if (page_len > len) {
-            goto invalid_param_len;
+            trace_scsi_disk_mode_select_page_truncated(page, page_len, len);
         }
 
         if (!change) {
diff --git a/hw/scsi/trace-events b/hw/scsi/trace-events
index e91b55a961..25eae9f307 100644
--- a/hw/scsi/trace-events
+++ b/hw/scsi/trace-events
@@ -339,6 +339,7 @@ scsi_disk_dma_command_READ(uint64_t lba, uint32_t len) 
"Read (sector %" PRId64 "
 scsi_disk_dma_command_WRITE(const char *cmd, uint64_t lba, int len) "Write 
%s(sector %" PRId64 ", count %u)"
 scsi_disk_new_request(uint32_t lun, uint32_t tag, const char *line) "Command: 
lun=%d tag=0x%x data=%s"
 scsi_disk_aio_sgio_command(uint32_t tag, uint8_t cmd, uint64_t lba, int len, 
uint32_t timeout) "disk aio sgio: tag=0x%x cmd=0x%x (sector %" PRId64 ", count 
%d) timeout=%u"
+scsi_disk_mode_select_page_truncated(int page, int len, int page_len) "page %d 
expected length %d but received length %d"
 
 # scsi-generic.c
 scsi_generic_command_complete_noio(void *req, uint32_t tag, int statuc) 
"Command complete %p tag=0x%x status=%d"
-- 
2.20.1