RE: iSCSI Boot: Technical Issues

[Luben Tuikov <ltuikov@yahoo.com>]

--- Black_David@emc.com wrote:
> Except that I think Luben got his left and right
> reversed ... how about:
> 
>       Within a group of 4 hexadecimal digits, leading
> 	zeros MAY be omitted, but at least one digit MUST
> 	be present if the group is not otherwise omitted.
> 	A trailing zero-valued group or groups MAY be omitted;
> 	the recipient MUST assume that omitted groups are zero
> 	and MUST suffix the zeroes to the right of the supplied
> 	groups.  A zero group that is to the left of any
> non-zero
> 	group MUST NOT be omitted.

With all due respect David, I do not have my left and right
reversed.

Your definition is more reminicent of _how_ to do it,
rather than the true formalizm of _what_ it is.
It is also too long, talks about recipient, etc,
which are NOT needed since the right/left rule can
be applied at either end to the same effect.

``Within each group of 4 hexacedimal digits zeros are
  filled to the right, and groups of zeros are filled
  to the left.''

This is a necessary and sufficient definition, the minimal
such, and one may derive all of the stipulations which
you've mentioned.

E.g. the fact that a leading 0000 group must not be
omitted,
is implicit in this definition. (else, the LUN
representation would be ambiguous, contrary to the
assumption that it is not.)

group: an ordered sequence of 4 hexadecimal digits.
      (ordered -- human brain assumes without question)

within each group ... filled to the right:
  4 --> 0004, and etc _recursively_ for as many groups
there'd be (max 4 groups in LUN), i.e. 4-4 -> 0004-0004

groups of zeros are filled to the left:
that is, this is done to complement to 4 groups,
e.g. from the previous example:
0004-0004 -> 0004-0004-0000-0000

The more challenging example 0-4-0-4 is left as
an exercise to the reader. :-)

Thus, one cannot assume that 4 can somehow be equivalent
to 0000-0004-0000-0000, because of the _left_ rule -- that
is groups of zeros are ONLY filled to the left!
(as the definition stipulates)

Nevertheless, the definition I gave is more mathematical,
and though clearer, succinct and straightforward, I can
see how the average reader could cough up reading it.

-- 
Luben





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