🚀 go-pugleaf

I have a driver for a SCSI-attached Epson 300C scanner working pretty well. The
code drives the scanner using /dev/sg0 using ioctl (opcodes C6OP_READ and
C6OP-WRITE). After much experimentation it appears there is a maximum number
of bytes of 256 I can read. When I issue an ioctl-read for > 256 bytes, I get a
error in sr_io_status (01x) and a sr_scsi_status of SENSE_NOTREADY.

Initially I tried to simply wait a little and retry, but I never get any other
status. I've tried clearing the attention with a sense and retry, but to no
avail. I have tried to break the read into several reads, but this too failed.
There is clearly something I do not understand and so far am unable to guess.
Everything works fine as along as the scanner generates <= 240 bytes per scan
line. As soon as the scanner tries to return > 240 bytes (I think the magic 
number of 256), the SENSE_NOTREADY begins to appear.

I'd appreciate some advice from you ioctl-gurus. Thanks!