Re: [PATCH 3/4] scsi: move target device list to xarray

[Matthew Wilcox <willy@infradead.org>]

On Thu, May 28, 2020 at 10:58:31PM +0200, Hannes Reinecke wrote:
> On 5/28/20 8:54 PM, Matthew Wilcox wrote:
> > On Thu, May 28, 2020 at 01:50:02PM -0400, Douglas Gilbert wrote:
> > > On 2020-05-28 12:36 p.m., Hannes Reinecke wrote:
> > > > Use xarray for device lookup by target. LUNs below 256 are linear,
> > > > and can be used directly as the index into the xarray.
> > > > LUNs above 256 have a distinct LUN format, and are not necessarily
> > > > linear. They'll be stored in indices above 256 in the xarray, with
> > > > the next free index in the xarray.
> > 
> > I don't understand why you think this is an improvement over just
> > using an allocating XArray for all LUNs.  It seems like more code,
> > and doesn't actually save you any storage space ... ?
> > 
> The LUN range is 64 bit.
> I was under the impression that xarray can only handle up to unsigned long;
> which probably would work for 64bit systems, but there _are_ users running
> on 32 bit, and they get patently unhappy when we have to tell them 'sorry,
> not for you'.

I meant just use xa_alloc() for everything instead of using xa_insert for
0-255.