Messages in this thread | | | Date | Thu, 01 Dec 2011 10:52:20 +0100 | From | Hannes Reinecke <> | Subject | Re: virtio-scsi spec (was Re: [PATCH] Add virtio-scsi to the virtio spec) |
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On 11/30/2011 05:36 PM, Paolo Bonzini wrote: > 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. > Virtio doesn't, but the underlying device/driver might. And if we don't expose these values we cannot format the request correctly.
>> 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? > I was thinking of something along the lines of the TransportID as defined in SPC. Main idea is to have a unique ID by which we can identify a given virtio-scsi host. Admittedly it might not be useful in general, so it might be an idea to delegate this to another controlq command.
>> 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. > Yes, for a a shared (physical) SCSI host persistent reservations will be tricky.
Cheers,
Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@suse.de +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: Markus Rex, HRB 16746 (AG Nürnberg)
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