Re: [PATCH RFC 0/9] [SCSI] Enhanced sense and Unit Attention handling

From: Hannes Reinecke <hare@suse.de>
To: Bart Van Assche <bart.vanassche@gmail.com>
Cc: "Ewan D. Milne" <emilne@redhat.com>, linux-scsi@vger.kernel.org
Subject: Re: [PATCH RFC 0/9] [SCSI] Enhanced sense and Unit Attention handling
Date: Thu, 24 Jan 2013 12:38:22 +0100	[thread overview]
Message-ID: <51011D2E.305@suse.de> (raw)
In-Reply-To: <CAO+b5-oKyPoSdKJPcyaf4FkDUNH25Cwwz=_C4WiwvpfauNqStQ@mail.gmail.com>

On 01/24/2013 01:19 AM, Bart Van Assche wrote:
> On Fri, Jan 18, 2013 at 9:27 AM, Ewan D. Milne <emilne@redhat.com> wrote:
>> This patch set adds changes to the SCSI mid-layer, sysfs and scsi_debug
>> to provide enhanced support for Unit Attention conditions, as well as
>> detection of reported sense data overflow conditions and some changes
>> to sense data processing.  It also adds a uevent when the reported
>> capacity changes on an sd device.
>>
>> There was some discussion about this a couple of years ago on the linux-scsi
>> mailing list:  http://marc.info/?l=linux-scsi&m=129702506514742&w=2
>> Although one approach is to send all SCSI sense data to a userspace daemon
>> for processing, this patch set does not take that approach due to the
>> difficulty in reliably delivering all of the data.  An interesting UA
>> condition might not be delivered due to a flood of media errors, for example.
>>
>> The mechanism used is to flag when certain UA ASC/ASCQ codes are received
>> that report asynchronous changes to the storage device configuration.
>> An appropriate uevent is then generated for the scsi_device or scsi_target
>> object.  An aggregation mechanism is used to avoid generating uevents at
>> too high a rate, and to coalesce multiple UAs reported by LUNs on the
>> same target for a REPORTED LUNS DATA HAS CHANGED sense code.
>
> Does this patch series add a function that allows SCSI LLDs to report
> AEN data to the SCSI core ? What if a SCSI target reports a LUN
> inventory change via AER to e.g. the iSCSI initiator and that
> initiator ignores the AEN data ? Will that result in AEN data being
> ignored and no automatic LUN rescanning ?
>
Well, first and foremost we _don't_ have automatic LUN rescanning.
This patchset just puts in the infrastructure that userspace can 
know _when_ a LUN rescan might be in order.

As for AEN, does iSCSI _do_ AEN? I thought it got removed ...

If it does, though, it should schedule an event on its own whenever 
an AER is received. The same goes for LLDDs with vendor-specific 
AENs; thinking of megaraid_sas here ...

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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