Re: Regarding ordered-tag support.

[Tejun <htejun@gmail.com>]

James Bottomley wrote:
> On Thu, 2006-02-09 at 01:57 +0900, Tejun wrote:
> 
>>I intentionally wrote 'driver' because if a SCSI device determines that 
>>it's busy, it would report via CHECK CONDITION.  Depending on QErr, the 
>>whole task set will be terminated, and such case falls into EH 
>>requeueing case (would require changes in scsi_softirq though).
> 
> No, it wouldn't.  BUSY is a SPI Message (deprecated on non-SPI
> transports) and QUEUE_FULL is a status return.  The device is entitled
> to think of the transaction as logically complete (and not impacting
> error recovery) after either of these returns.

I see.  I'll dig docs.

>>>You're making the assumption that you can set QErr... It's under device control. 
>>
>>Was it ro field?  Didn't know that.  I will check it tomorrow.  If a 
>>device doesn't abort whole taskset, we just can't use ordered-tag for 
>>barriers.
> 
> 
> His point is that it's a field in the mode page of a device.  Some
> devices only have read only mode pages ... still more may not act on
> this field correctly even if set.  Basically it's opening a can of
> worms.

Yeah, I kind of doubt whether hardware vendors would implement and test
all the options and features whene I read SCSI specs.  Considering how
many ATA drives have faulty firmware...

Anyways, it seems ordered-tag support should be left alone for the time
being.  Sad.  :-(

Thanks a lot.

-- 
tejun