Re: [PATCH] SCSI driver for VMware's virtual HBA.

From: James Bottomley
Date: Tue Sep 01 2009 - 10:23:51 EST

On Mon, 2009-08-31 at 14:53 -0700, Alok Kataria wrote:
> Hi James,
> Thanks for your comments.
> On Mon, 2009-08-31 at 11:00 -0700, James Bottomley wrote:
> > On Mon, 2009-08-31 at 10:28 -0700, Alok Kataria wrote:
> > > VMware PVSCSI driver - v2.
> >
> > OK, so the first thing that springs to mind is that we already have one
> > of these things: the ibmvscsi ... is there no way we can share code
> > between this and the other PV drivers?
> I took a quick look at the ibmvscsi driver, and there are lot of
> differences between the two, mainly the ABI that is shared between the
> hypervisor and driver differ.

Well, that's pretty abstractable, surely? However, there is an
interesting question of what the best hypervisor interface actually is.

> Also the ibmvscsi driver seems to offer a
> lot of other features as well, like the SRP.

SRP is the protocol transfer abstraction. It's just a way of packaging
up SCSI commands for transfer over a DMA protocol (OK, so it was
envisaged that the DMA protocol would be RDMA, but a hypervisor
interface is also a DMA protocol).

> The pvscsi driver is a simple SCSI adapter driver and is basically no
> different than any other SCSI driver written for a particular HBA.

Well, it is really ... hopefully all the hypervisor interfaces won't
decide to be completely incompatible, so there's a good chance of code
sharing between them.


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