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xen-devel
[Xen-devel] Re: [RFC PATCH 35/35] Add Xen virtual block device driver.
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To: |
Jeff Garzik <jeff@xxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: [RFC PATCH 35/35] Add Xen virtual block device driver. |
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From: |
Peter Chubb <peterc@xxxxxxxxxxxxxxxxxx> |
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Date: |
Mon, 27 Mar 2006 21:14:23 +1100 |
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Cc: |
Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, SCSI Mailing List <linux-scsi@xxxxxxxxxxxxxxx>, Ian Pratt <ian.pratt@xxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, Chris Wright <chrisw@xxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx |
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Hyperbole mail buttons accepted, v04.18. |
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>>>>> "Jeff" == Jeff Garzik <jeff@xxxxxxxxxx> writes:
Jeff> Ian Pratt wrote:
>>
>> We certainly should be pushing everyone toward using the 'xdX' etc
>> devices that are allocated to us. However, the installers of
>> certain older distros and other user space tools won't except
>> anything other than hdX/sdX, so its useful from a compatibility POV
>> even if it never goes into mainline, which I agree it probably
>> shouldn't.
Jeff> Yes, this is true. Red Hat installer guys grumbled at me when I
Jeff> wrote the 'sx8' block driver: since it wasn't hda/sda, they had
Jeff> to write special code for it, as they apparently must do for any
Jeff> new block driver "class". SuSE and other distros are probably
Jeff> similar, since each block driver provides its own special
Jeff> behaviors and feature exports.
Jeff> I should have spoken up a long time ago about this, but anyway:
Jeff> An IBM hypervisor on ppc64 communicates uses SCSI RPC messages.
Jeff> I think this would be quite nice for Xen, because SCSI (a) is a
Jeff> message-based model, and (b) implementing block using SCSI has a
Jeff> very high Just Works(tm) value which cannot be ignored. And
Jeff> perhaps (c) SCSI target code already exists, so implementing the
Jeff> server side doesn't require starting from scratch, but rather
Jeff> simply connecting the Legos.
The IA64 virtualisation work (Xen and Linux-on-Linux) uses the SKI
simulator virtual scsi device --- which looks just like any other scsi
disk, but uses hypervisor calls to do read/write/open/close calls like
a user-mode process. For performance, it needs to be extended a bit
to do asynchronous I/O and interrupt on completion. As a halfway
house, the ski simscsi driver would be fairly easy to port, I think.
--
Dr Peter Chubb http://www.gelato.unsw.edu.au peterc AT gelato.unsw.edu.au
http://www.ertos.nicta.com.au ERTOS within National ICT Australia
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