Decoding short sense buffers

Decoding short sense buffers

[Hannes Reinecke]

Hi all,

I've noticed that virtually everybody assumes that the length of the 
sense buffer is SCSI_SENSE_BUFFERSIZE.
And consequently every caller uses SCSI_SENSE_BUFFERSIZE when 
calling any of the sense processing functions like
scsi_normalize_sense() etc.

However, those processing functions to go into great detail handling 
_shorter_ buffersizes, which of course will never happen.

On the other hand, most LLDDs are capable of detecting the actually 
transmitted sense buffer sizes; there even is a field in struct 
request which would allow us to transmit the number of bytes in the 
sense buffer.
But this field is happily neglected, too.

So, questions here:
- Do we actually care for a sense buffer underflow?
We won't be able to detect it currently anyway;
plus we haven't received any error reports for it.
And the allocated sense buffer is _always_ SCSI_SENSE_BUFFERSIZE ...

- What is the intention of rq->sense_len?
 From what I gather it _should_ hold the size of the received sense 
buffer data. But that doesn't happen currently.
For short sense buffers that doesn't matter, but for sense buffer 
_overruns_ it would be quite good to know.

Which causes quite some confusion on how to probe for valid sense data:
- DRIVER_SENSE ?
- rq->sense_len?
- scsi_normalize_sense?

Thanks for clarification.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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