Re: ioctls, etc. (was Re: [PATCH 1/4] sas: add flag for locally attached PHYs)

Douglas Gilbert
2005-10-22T02:29:34Z

Matthew Wilcox wrote:
> On Fri, Oct 21, 2005 at 02:12:49PM -0400, Luben Tuikov wrote:
>
>>>That beeing said I tried this approach. It looks pretty cool when you
>>>think about it, but the block layer is quite a bit too heavyweight for
>>>queueing up a few SMP requests, and we need to carry too much useless
>>>code around for it.
>>
>>That's the last reason not to implement SMP as a block device.
>>But this is good that you tried it and it "flopped". This way
>>people will stop repeating "SMP... block device".
>
>
> Block layer != Block device.
>
> Nobody wants to implement SMP as a block device.
>
> The question is whether the SMP interface should be implemented as part
> of the block layer.

However, the block layer is used in the context of a
block device (and in some cases a char device).
If SAS domain discovery is done from the user space, and
the root file system is the far side of a SAS expander,
there are no suitable devices, just the SAS initiator
(HBA) which currently we cannot address via the block layer.

Doug Gilbert