Re: [RFC] SAS domain layout for Linux sysfs

[Christoph Hellwig <hch@infradead.org>]

On Mon, Apr 25, 2005 at 12:06:10PM -0400, Luben Tuikov wrote:
> On 04/24/05 07:19, Christoph Hellwig wrote:
> > 
> > This is contrary to any sysfs topology I know about, especially any
> > existing transport class (SPI, FC, iSCSI).
> 
> This RFC is about SAS.

But our SAS transport class should be consistant with the other transport
classes.

> >  We only ever care about what's seen from a HA,
> 
> Imagine you could connect to the same device via two
> different PCI controllers on the same host.

Which is exactly the case in the examples I've mentioned.

> 
> > e.g. if you have muliple SPI cards that are
> > on a single parallel bus you'll have the same bus represented twice,
> > similarly if you have two fibre channel HBAs connected to the same
> > SAN you'll have the SAN topology duplicated in both sub-topologies.
> 
> Hmm, this proposal is for SAS only, Christoph.
> 
> If you have multiple SAS host adapters connected to the same
> SAS domain, the _path_ they connect to a SAS device may be _different_.
> But what is the same is the SAS domain (topology) itself *regardless of
> how you connect to it.*
> 
> In order to eliminate duplication of sysfs entries (directories
> and files) to describe the same SAS device, we split up the
> representation into a "flat" directory with just a bunch
> of SAS devices, this is /sys/bus/sas/.  And the way you _connect_
> to those SAS devices is represented in sys/class/sas_ha/.

Please read the previous mail again, you're not getting it at all.

If you don't understand the problems it's not worth talking about more.