Help - a question on scsi_debug and mid-layer

Help - a question on scsi_debug and mid-layer

[Lee Xing]

Hi,

I'm playing with scsi_debug (a low-level driver) of lk2.4 and notice that scsi_debug_queuecommand(...) defined in scsi_debug returns sometimes before the SCSI command completes (i.e. before done(cmd) is invoked), and sometimes after done(cmd) is invoked.  Can SCSI mid-layer really handle both cases without any problems, and why?

I assume that before scsi_debug_queuecommand() returns the control to mid-layer, mid-layer has no way to know whether that SCSI command has been successfully queued in low-level driver, therefore scsi_debug should not invoke done(cmd) before completing scsi_debug_queuecommand(...), correct?

Thanks,


T.

Lee Xing
Crossroads Systems, Inc.
(512) 928-7297

Re: Help - a question on scsi_debug and mid-layer

[James Bottomley]

On Mon, 2004-06-21 at 13:53, Lee Xing wrote:
> I'm playing with scsi_debug (a low-level driver) of lk2.4 and notice that scsi_debug_queuecommand(...) defined in scsi_debug returns sometimes before the SCSI command completes (i.e. before done(cmd) is invoked), and sometimes after done(cmd) is invoked.  Can SCSI mid-layer really handle both cases without any problems, and why?
> 
> I assume that before scsi_debug_queuecommand() returns the control to mid-layer, mid-layer has no way to know whether that SCSI command has been successfully queued in low-level driver, therefore scsi_debug should not invoke done(cmd) before completing scsi_debug_queuecommand(...), correct?

I think if you look in Documentation/scsi/scsi_mid_low_api.txt (on 2.6)
you'll find it explains all of this under the entry for queuecommand.

James