Messages in this thread |  | | Date | Wed, 30 Nov 2011 17:36:52 +0100 | | From | Paolo Bonzini <> | | Subject | Re: virtio-scsi spec (was Re: [PATCH] Add virtio-scsi to the virtio spec) |
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On 11/30/2011 03:17 PM, Hannes Reinecke wrote: >> seg_max is the maximum number of segments that can be in a >> command. A bidirectional command can include seg_max input >> segments and seg_max output segments. >> > I would like to have the other request_queue limitations exposed > here, too. > Most notably we're missing the maximum size of an individual segment > and the maximum size of the overall I/O request.
The virtio transport does not put any limit, as far as I know.
> As this is the host specification I really would like to see an host > identifier somewhere in there. > Otherwise we won't be able to reliably identify a virtio SCSI host.
I thought about it, but I couldn't figure out exactly how to use it. If it's just allocating 64 bits in the configuration space (with the stipulation that they could be zero), let's do it now. Otherwise a controlq command is indeed better, and it can come later.
But even if it's just a 64-bit value, then: 1) where would you place it in sysfs for userspace? I can make up a random name, but existing user tools won't find it and that's against the design of virtio-scsi. 2) How would it be encoded as a transport ID? Is it FC, or firewire, or SAS, or what?
> Plus you can't calculate the ITL nexus information, making > Persistent Reservations impossible.
They are not impossible, only some features such as SPEC_I_PT. If you use NPIV or iSCSI in the host, then the persistent reservations will already get the correct initiator port. If not, much more work is needed.
> We should be adding > > VIRTIO_SCSI_S_BUSY > > for a temporary failure, indicating that a command retry > might be sufficient to clear this situation. > Equivalent to VIRTIO_SCSI_S_NEXUS_FAILURE, but issuing a retry on > the same path.
... and equivalent to DID_BUS_BUSY. Assuming no other major objections, I will add and resubmit in a few days.
Paolo
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