Re: [PATCH][RFC] scsi: Use W_LUN for scanning

[Douglas Gilbert <dgilbert@interlog.com>]

On 13-03-15 05:46 AM, Hannes Reinecke wrote:
> SAM advertises the use of a Well-known LUN (W_LUN) for scanning.
> As this avoids exposing LUN 0 (which might be a valid LUN) for
> all initiators it is the preferred method for LUN scanning on
> some arrays.
> So we should be using W_LUN for scanning, too. If the W_LUN is
> not supported we'll fall back to use LUN 0.
> For broken W_LUN implementations a new blacklist flag
> 'BLIST_NO_WLUN' is added.

There are proposals at T10 for feature sets to be added to
SCSI (similar to what ATA devices have). Perhaps we could
have something similar at the OS level: an opaque call
that makes some general decisions based on what we know
about the transport, HBA and possibly target/LU. So if
we are looking at a USB transport not doing UASP, then
prefer to probe LUN 0 rather than the to probe via
REPORT LUNS W_LUN. Many other (somewhat) advanced SCSI
techniques could be filtered in a similar way (e.g. if
it's a USB device assume badly implemented SCSI-2
compliance).

We could still keep the blacklist and, if we don't already
have it, add whitelist logic (e.g. for 0.001% of well-behaved
USB devices).

Doug Gilbert