[PATCH] libata-scsi: be tolerant of 12-byte ATAPI commands in 16-byte CDBs

[Mark Lord <liml@rtr.ca>]

Sebastian Kemper reported that issuing CD/DVD commands under libata
is not fully compatible with ide-scsi.  In particular, the GPCMD_SET_STREAMING
was being rejected at the host level in some instances.

The reason is that libata-scsi insists upon the cmd_len field exactly matching
the SCSI opcode being issued, whereas ide-scsi tolerates 12-byte commands
contained within a 16-byte (cmd_len) CDB.

There doesn't seem to be a good reason for us to not be compatible there,
so here is a patch to fix libata-scsi to permit SCSI opcodes so long as
they fit within whatever size CDB is provided.

Signed-off-by: Mark Lord <mlord@pobox.com>
---

Patch is against 2.6.24-rc2-git4.
Sebastian, could you please re-test with this patch
and let us know that it works for you (or not).

--- old/drivers/ata/libata-scsi.c	2007-11-13 23:25:15.000000000 -0500
+++ linux/drivers/ata/libata-scsi.c	2007-11-14 12:32:16.000000000 -0500
@@ -2869,7 +2869,8 @@
 		xlat_func = NULL;
 		if (likely((scsi_op != ATA_16) || !atapi_passthru16)) {
 			/* relay SCSI command to ATAPI device */
-			if (unlikely(scmd->cmd_len > dev->cdb_len))
+			int len = COMMAND_SIZE(scsi_op);
+			if (unlikely(len > scmd->cmd_len || len > dev->cdb_len))
 				goto bad_cdb_len;
 
 			xlat_func = atapi_xlat;