Re: [PATCH] allow drivers to hook into watchdog timeout

["Justin T. Gibbs" <gibbs@scsiguy.com>]

> On Tue, 2004-02-10 at 14:44, Justin T. Gibbs wrote:
>> > If you need to stall a command after you've accepted it by returning
>> > zero from queuecommand, you return it to the mid-layer with status
>> > either BUSY or QUEUE_FULL.
>> 
>> BUSY and QUEUE_FULL status have particular meanings when associated
>> with an SCSI peripheral.  Using them for this purpose will only confuse
>> the mid-layer into taking unwarranted action, like trying to throttle
>> the queue depth.  The times that I want to use this have nothing to
>> do with BUSY or QUEUE_FULL in their SCSI sense.
> 
> So if I give you an error code for this, like DID_REQEUEUE, you'll
> eliminate the driver queueing from your queucommand and from your done
> processing?

If I can freeze at per-device granularity and testing of the BUSY and
QUEUE_FULL paths in the mid-layer pan out, I believe the answer is yes.

>> They will only be issued up to their command retry count which may be zero
>> for certain commands.  This may also confuse the peripheral or mid-layer
>> drivers into believing that a unit attention condition is expected and
>> should be ignored.  The commands that were affected by the recovery action
>> should be marked accordingly, but marking the commands that are still waiting
>> on the sidelines is the equivalent of a drive-by-shooting.
> 
> No, they won't.  DID_RESET doesn't count against the retry count (the
> only things that affect the retry count are conditions that go through
> the maybe_retry label in scsi_device_disposition()).

This is only true if the peripheral driver calls scsi_io_completion().
The SG driver, for instance, does not.

> It will not cause any unit attention exception processing.  That only
> happens if the error handler knows it reset something, or the driver
> reports that it is resetting something.

That reminds me.  Reported bus/target resets do not cause a
bus/device-settle delay.  This is another one of the workarounds
in my driver.

--
Justin