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xen-devel
[Xen-devel] Re: [kvm-devel] [PATCH RFC 3/3] virtio infrastructure: examp
 
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To:  | 
Rusty Russell <rusty@xxxxxxxxxxxxxxx> | 
 
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Subject:  | 
[Xen-devel] Re: [kvm-devel] [PATCH RFC 3/3] virtio infrastructure: example block driver | 
 
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From:  | 
Carsten Otte <cotte@xxxxxxxxxx> | 
 
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Date:  | 
Thu, 31 May 2007 14:57:27 +0200 | 
 
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Cc:  | 
Jimi Xenidis <jimix@xxxxxxxxxxxxxx>,	Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>,	Xen Mailing List <xen-devel@xxxxxxxxxxxxxxxxxxx>,	"jmk@xxxxxxxxxxxxxxxxxxx" <jmk@xxxxxxxxxxxxxxxxxxx>,	Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>,	kvm-devel <kvm-devel@xxxxxxxxxxxxxxxxxxxxx>, mschwid2@xxxxxxxxxxxxxxxxxx,	virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>,	Christian Borntraeger <cborntra@xxxxxxxxxx>,	Suzanne McIntosh <skranjac@xxxxxxxxxx> | 
 
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Thu, 31 May 2007 10:28:33 -0700 | 
 
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Rusty Russell wrote:
 
Example block driver using virtio.
The block driver uses outbufs with sg[0] being the request information
(struct virtio_blk_outhdr) with the type, sector and inbuf id.  For a
write, the rest of the sg will contain the data to be written.
The first segment of the inbuf is a result code (struct
virtio_blk_inhdr).  For a read, the rest of the sg points to the input
buffer.
TODO:
        1) Ordered tag support.
 Implementing a do_request function has quite a few disadvantages over 
hooking into q->make_request_fn. This way, we have the device plug 
(latency), request merging, and I/O scheduling inside the guest.
It seems preferable to do that in the host, especially when requests 
of multiple guests end up on the same physical media (shared access, 
or partitioned).
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