linux-kernel - Re: [PATCH 11/9] firewire: fw-sbp2: enforce a retry of __scsi_add

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Message-ID: <47ACB449.3060200@s5r6.in-berlin.de>
Date:	Fri, 08 Feb 2008 20:58:01 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Jarod Wilson <jwilson@...hat.com>
CC:	linux1394-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: [PATCH 11/9] firewire: fw-sbp2: enforce a retry of __scsi_add_device
 if bus generation changed

(Adding Cc: LSML)

Jarod Wilson wrote:
> On Wednesday 06 February 2008 04:09:47 pm Stefan Richter wrote:
>> take care that __scsi_add_device does not return success
>> even though the SCSI high-level driver probing failed (sd READ_CAPACITY
>> and friends) due to bus reset.  The trick to do so is to use a different
>> error indicator in the command completion as long as __scsi_add_device
>> did not return.

Or so did I guess, and...

>> An actual failure of __scsi_add_device is easy to handle, but an
>> incomplete execution of __scsi_add_device with an sdev returned would
>> remain undetected and leave the SBP-2 target unusable.
>>
>> Signed-off-by: Stefan Richter <stefanr@...6.in-berlin.de>
>> ---
>>
>> Jarod, does this work like I assume and fixes your setup of two OXFW911
>> based disks?
> 
> Well, it results in the dmesg spew saying "sd 6:0:0:0: [sdc] Result: 
> hostbyte=DID_NO_CONNECT driverbyte=DRIVER_OK,SUGGEST_OK" -- i.e., 
> DID_NO_CONNECT instead of DID_BUS_BUSY, but other than that, no change in 
> behavior, sdc remains unusable just as before.

...my guess was wrong then.

Either I misunderstood the semantics of the various hostbyte codes in
the command completion return (and then these semantics are
insufficient) --- or SCSI mid layer or high-level implements them wrong.

But before we dive into the SCSI stack or implement parellelism of SBP-2
reconnect and SCSI probing in fw-sbp2, there is another simple and in
hindsight obvious trick we can try.  Stay tuned.

Background for LSML:

In case of unrecoverable transport failures during the execution of
__scsi_add_device, I would like to send appropriate error indicators
from the LLD up to SCSI midlayer so that __scsi_add_device ends in
failure (i.e. returns an error pointer rather than a scsi_device pointer).

Sometimes SCSI core decides to let __scsi_add_device fail, sometimes it
takes the scsi_device offline, sometimes it doesn't do either but
pretends to the LLD that __scsi_add_device was an utter success.  Except
that userspace can't do anything with the scsi_device because e.g. READ
CAPACITY couldn't be executed.
-- 
Stefan Richter
-=====-==--- --=- -=---
http://arcgraph.de/sr/
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