legal but rude
LAVARRE at iomega.com
Fri Feb 21 10:28:55 PST 2003
* From the T10 Reflector (t10 at t10.org), posted by:
* "Pat LaVarre" <LAVARRE at iomega.com>
By the way, I find a number of engineers find the "legal but rude" concept difficult to learn.
Anybody got a better way to explain it?
The kind of design I mean by this phrase includes choosing plug 'n play descriptors, such as op x12 Inquiry data, formed strictly in accord with the merely public merely standard paper specs ... that in fact don't interoperate well because they aren't normal. Of course I can't easily discuss any real & current examples, but here's an analogous hypothetical.
Suppose someone actually built a device with an op x12 Inquiry that returned x00 DASD as the byte 0 & x1F PDT (PeripheralDeviceType) but then responded to op x25 ReadCapacity with a blockLength larger than x1000 B = 4KiB.
All the paper specs say this is utterly legit. But if you actually go build such a thing, the host i/o chokes, because "everyone knows" that the block size of any HDD is supposed to be as small or smaller than a virtual memory page, and "almot everyone knows" that the block size of x00 DASD is supposed to be x200 B = 512 B = 0.5KiB.
I say the device and the host here are being "rude". This other engineer said only the host was "rude", because the paper spec covers the device, so the device is "legal", and there is no paper spec for the host. I say neither would have got caught being rude if the other had been polite. I say we know they are mutually rude because the system breaks, despite half of the system, the device, being completely legal by any reasonable reading of the merely public merely standard paper specs.
What can this engineer be thinking, to say only the host is rude?
How can I explain that the device here is equally rude?
Cluelessly, curiously, thankfully yours, and a Happy Friday to you, Pat LaVarre
P.S. If by chance I err and some paper spec does tell us that block size other than 0.5 KiB isn't legal for PDT = x00 DASD, that rather misses the point. The point is we can tell it's rude before we even ask if it's legal.
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