I'm wondering how to determine the correct IORequest size for a particular device driver? For eaxmple if one was opening a device that could be SCSI, IDE or USB how do you find out the correct IO block size? Is there a generic size? I've seen IOExtTD used but does this cover all bases?
On a related note I wonder how the filesystem figures this out? Since it is given device and unit only AFAIK. I see no mention of IO block size. Since it can differ between devices I wonder what a safe size would be. :-)