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

From: Ric Wheeler
Date: Thu Sep 03 2009 - 17:27:53 EST

On 09/03/2009 04:31 PM, Dmitry Torokhov wrote:
On Thursday 03 September 2009 01:03:02 pm James Bottomley wrote:
I'm not really asking you to standardise anything (yet). I was more
probing for why you hadn't included any of the SCSI control plane
interfaces and what lead you do produce a different design from the
current patterns in virtual I/O. I think what I'm hearing is "Because
we didn't look at how modern SCSI drivers are constructed" and "Because
we didn't look at how virtual I/O is currently done in Linux". That's
OK (it's depressingly familiar in drivers),
I am sorry that's not the case, the reason we have different design as I
have mentioned above is because we want a generic mechanism which works
for all/most of the GOS's out their and doesn't need to be specific to
Slightly confused now ... you're saying you did look at the transport
class and virtio? But you chose not to do a virtio like interface (for
reasons which I'm still not clear on) ...
Virtio is Linux-specific and is not available on older kernels which
our hypervisor/PVSCSI combination does support. Even if we were to use
virtio-like schema in the hypervisor code we would have to re-implement
much of the virtio code for kernels earlier than those shipped in '07
and do the same for other operating systems for no apparent benefit.
The PCI device abstraction is self-contained and works well on Windows,
Linux and other guest operating systems and so it was chosen.

Several arguments have a history of never winning when you try to get a new bit of code in linux.

Number one in the bad justifications is that your design is good because it avoids being "linux specific" closely followed by needing to backport :-)


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