SAM-3 status codes

The perverse CHECK_CONDITION in include/scsi/scsi.h seems to have struck again (see "Can't burn DVD under 2.5.59 with ide-cd" thread on the linux kernel list). Most users of CHECK_CONDITION found out to their surprise that it is shifted 1 bit (right) from those values found in the standards.

The attachment marks the orginal list of SCSI status codes as deprecated and supplies defines taken from the most recent SAM-3 draft.

The patch is against 2.5.59 but may also be suitable for the lk 2.4 tree.

Doug Gilbert

@@ -104,7 +104,26 @@
 
 
 /*
- *  Status codes
+ *  SCSI Architecture Model (SAM) Status codes. Taken from SAM-3 draft
+ *  T10/1561-D Revision 4 Draft dated 7th November 2002.
+ */
+#define SAM_STAT_GOOD            0x00
+#define SAM_STAT_CHECK_CONDITION 0x02
+#define SAM_STAT_CONDITION_MET   0x04
+#define SAM_STAT_BUSY            0x08
+#define SAM_STAT_IMMEDIATE       0x10
+#define SAM_STAT_IMMEDIATE_CONDITION_MET 0x14
+#define SAM_STAT_RESERVATION_CONFLICT 0x18
+#define SAM_STAT_COMMAND_TERMINATED 0x22	/* obsolete in SAM-3 */
+#define SAM_STAT_TASK_SET_FULL   0x28
+#define SAM_STAT_ACA_ACTIVE      0x30
+#define SAM_STAT_TASK_ABORTED    0x40
+
+/*
+ *  Status codes. These are deprecated as they are shifted 1 bit right
+ *  from those found in the SCSI standards. This causes confusion for
+ *  applications that are ported to several OSes. Prefer SAM Status codes
+ *  above.
  */
 
 #define GOOD                 0x00

WOOHOO !

Thank you sir!

Andre Hedrick
LAD Storage Consulting Group

Thanks Doug, the old defines were really sick, dunno who was smoking what. I not so sure I like the naming, though. The old ones still have the most obvious naming :(

Jens Axboe

Jens,

One of the problems is chasing down all the variations of SAM and pre SAM. I do not know, and maybe Doug can help, but did bit0 become obsoleted in the age of SASI's transformation to SCSI ?

I can not find anything about it, and my knowledge in the history of SCSI is vastly weaker then ATA during the X3 split.

The naming issue is what stopped me in the process of working on a bus-phase rewrite to convert scsi to a logical state machine. Dealing with all the issues related to the HBA's was more than any mad man could attempt, much less a sane one.

Comments on fixing 2.5 to use proper status values?

Cheers,

Andre Hedrick
LAD Storage Consulting Group

In SCSI-2 bits 0, 6 and 7 of the status byte were reserved for the _implementation_. Not sure if any SCSI devices every used them because that would make this code:
if (status == SCSI_CHECK_CONDITION) ....
problematic. [It should be:
if (status & SCSI_CHECK_CONDITION) ...
which also correctly picks up COMMAND_TERMINATED but you don't see code like that very often.]
BTW There is a '#define SCSI_MASK 0x3e' in
the scsi.h header allowing:
if ((status & SCSI_MASK) == SCSI_CHECK_CONDITION) ...

In SCSI 3 (or later) bits 0 and 7 are reserved (period) and bit 6 is in use. The masking that was (strictly speaking) required in SCSI-2 seems to be no longer required.

Well, the only problem is that CHECK_CONDITION in /usr/src/linux/include/scsi/scsi.h is visible to the user space (and is replicated in RH8.0's /usr/include/scsi/scsi.h by the glibc people). It would be surprising if Joerg Schilling (cdrecord) used it but I should check SANE and a few other long term sg users. scsiinfo + sg(3)_utils don't use it.

If we don't cause user space pain and we can change the kernel code that uses CHECK_CONDITION (and friends) then we could make the change in lk 2.5 . Some names are still not ideal (e.g. "GOOD") so prefixing them with SCSI_ or SAM_ still might be useful.
That is replace:

  #define GOOD                 0x00
  #define CHECK_CONDITION      0x01
  #define CONDITION_GOOD       0x02
  #define BUSY                 0x04
  #define INTERMEDIATE_GOOD    0x08
  #define INTERMEDIATE_C_GOOD  0x0a

#define RESERVATION_CONFLICT 0x0c
#define COMMAND_TERMINATED 0x11
#define QUEUE_FULL 0x14

  #define STATUS_MASK          0x3e

with:

  #define SAM_GOOD            0x00
  #define SAM_CHECK_CONDITION 0x02
  #define SAM_CONDITION_MET   0x04
  #define SAM_BUSY            0x08
  #define SAM_IMMEDIATE       0x10
  #define SAM_IMMEDIATE_CONDITION_MET 0x14
  #define SAM_RESERVATION_CONFLICT 0x18
  #define SAM_COMMAND_TERMINATED 0x22       /* obsolete in SAM-3 */
  #define SAM_TASK_SET_FULL   0x28
  #define SAM_ACA_ACTIVE      0x30
  #define SAM_TASK_ABORTED    0x40

  #define SCSI2_MASK          0x3e
  #define SAM3_MASK           0x7e

Doug Gilbert