I am currently writing a low-level SCSI device driver which has the
requirement that the largest op that can be issued to it is 256k. It
appears as if there is not an architected way for the low level to
communicate this to the upper levels. I am currently limiting the number of
scatter/gather elements to 64 and relying that an element can not be larger
than 4k (this adapter is not going to run on hardware with anything other
than a 4k page size). There are comments in the scsi merging code that
there is a desire for this requirement to go away in the future and when it
does, scatter/gather elements could be > 4K. It appears to me that it would
be reasonable for the max op size (MAX_SECTORS) to be a parameter on the
host structure just like num_sg is today. I know I am not the first to
encounter this issue (The IBM ServeRAID card, I believe, recently added
some code in their device driver to split up ops, which seems like a very
distateful solution to me). Has this been discussed before?
Brian King
Advanced Function Storage Firmware Development
Dept. CC7/050-3 E209 T/L 8-553-8636
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