HEADS UP: SCSI device specific timeouts

[Frank Kardel <kardel%netbsd.org@localhost>]

Hi!

I just committed fetching device specific timeout values from SCSI devices.

The benefit is that we do not abort a perfectly running SCSI commands 
with device reset before its device provided timeout and thus gain
more reliability with slower devices.

The timeout values are loaded at attachment time if the device supports 
them,
If the timeout information is available it shows up as "timeout-info" in 
dmesg like this:

st0 at scsibus0 target 9 lun 0: <IBM, ULTRIUM-HH7, J4D1> tape removable 
timeout-info
st0: density code 92, variable blocks, write-enabled

This mechanism is disabled for USB umass devices as some of these may 
get into strange
states when the SCSI command is sent.

The code has been tested with SCSI tapes, changers and disks. The newer 
tapes provide the timeout information and thus
some helpful longer timeouts like TUR 60 sec instead of our default of 
15 sec and WRITE ~1500 sec instead of 120 sec.

So, if anything gets now stuck at SCSI attachment time it might be the 
new MAINTENANCE_IN/REPORT_SUPPORTED_OPCODES
query and thus might just need a quirk. Hopefully there are not many of 
these devices.

Best regards,
  Frank