Pack of CAM improvements

Alexander Motin mav at
Sun Jan 24 16:49:15 UTC 2010

Gary Jennejohn wrote:
> I started seeing a problem a few days ago with one of my DVD drives (a
> burner at cd0) under 9-current, which makes it impossible to use it even
> to simply read a DVD.
> Here the (rather strange IMO) output in dmesg:
> cd0: <HL-DT-ST DVD-RAM GSA-H54N 1.00> Removable CD-ROM SCSI-0 device
> cd0: 66.700MB/s transfers (UDMA4, PIO size 65534bytes)
> cd0: Attempt to query device size failed: UNIT ATTENTION, Power on, reset,
> or bus device reset occurred
> cd1 at ata0 bus 0 scbus6 target 1 lun 0
> cd1: <TSSTcorp DVD-ROM SH-D162D SB01> Removable CD-ROM SCSI-0 device
> cd1: 33.300MB/s transfers (UDMA2, PIO size 65534bytes)
> cd1: Attempt to query device size failed: NOT READY, Medium not present -
> tray closed
> I haven't the foggiest why cd0 behaves diffrently from cd1, which is a
> vanilla DVD drive and just works.

I am not sure yet what triggered these changes. May be just some timing
issue. That UNIT ATTENTION seems reasonable, as reset indeed just
happened there. The real problem is that CAM had several limitations in
SCSI status handling, when working with ATAPI or USB devices. It made
request processing stop in some cases, where retries would be expected.

New patch version should handle this and some other problems:

Try it please. Thanks.

Alexander Motin

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