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[Xen-devel] Re: [kvm-devel] [PATCH RFC 3/3] virtio infrastructure: examp

To: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [kvm-devel] [PATCH RFC 3/3] virtio infrastructure: example block driver
From: Carsten Otte <cotte@xxxxxxxxxx>
Date: Thu, 31 May 2007 14:57:27 +0200
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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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

        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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