Re: [PATCH 2/3] Add EVPD page 0x83 to sysfs

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Fri, 2014-03-07 at 02:43 -0800, Christoph Hellwig wrote:
> On Fri, Mar 07, 2014 at 02:40:00PM +0400, James Bottomley wrote:
> > On Thu, 2014-03-06 at 10:01 +0100, Hannes Reinecke wrote:
> > > So the only 'proper' solution would be to add a bitmap of supported
> > > pages; however, this would be 256 bits = 32 bytes of additional
> > > space required for struct sdev.
> > > Which I'm a bit reluctant do to, as it'll be a sparse array in most
> > > cases, adding to quite some wasted space.
> > 
> > Why per sdev?  Isn't it per target?  The supported EVPD page list
> > shouldn't really vary for luns of the same target unless something very
> > strange is happening in the array.
> 
> It might very well vary.  For one difference device types support
> different EVPD patches and a target might mix and match device types for
> LUNs.

Yes, cardreaders can do this, I suppose, but they're not a usual case

>   Also software targets might use individual LUNs as passthrough
> to physical devices, in which case they might support different EVPD
> pages even for the same device type.  E.g. the pscsi backend for the
> in-kernel target might behave like that.

This is a bit of a stretch too.  However, I can't see an easy way of
supporting the common case (same EVPD array per lun) simply and allowing
for the more complex one, so I suppose if we do it it will have to be
per sdev.

James