The trusted environment question

Bob Snively Bob.Snively at eng.sun.com
Mon Apr 25 18:27:20 PDT 1994


	
Review of the FCP has shown the following problems in SAM 12A that
need to be reviewed.


Comment 1	Reserved Field (Technical)

Section 2.4, page 17, is excessively restrictive.  

a)	It makes the assumption that SCSI devices cannot to
	be treated as trusted partners.  In fact, it is impossible
	for any SCSI device to thoroughly analyze the possible
	invalidity of each nuance of protocol and data structure
	in a meaningful manner.  The SCSI devices have to be expected
	to obey the restrictions placed on them by the standards.
	Such analysis should be performed during the design, debug,
	and integration of a SCSI device into a system, not during 
	normal operation.

b)	It provides only one recovery mechanism for any data structure 
	defined in any SCSI-3 standard.  Data structures defined for
	software interfaces or messages use other notification
	mechanisms for indicating invalid values.

c)	The section disallows the use of compatible extensions
	that make use of data that is ignored by previous generations
	of devices. 

I would suggest that the wording similar to the convention of FC-PH 
regarding the word "shall" be used.  The added text would then indicate:

"The term "shall" is used to indicate a mandatory rule.  If such a rule
is not followed, the results are unpredictable unless indicated otherwise."

"For all SCSI-3 standards, the term "reserved" is used to indicate 
that a field or code value
within a data structure is set aside for future standardization.
A reserved field shall be set to zero or in accordance with a future
extension to the defining SCSI-3 standard.  A reserved code value
shall not be used except in accordance with a future extension to the
defining SCSI-3 standard.  If these rules are not
followed, the results are unpredictable unless indicated otherwise."




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