Re: [PATCH] virtio-blk: add SGI_IO passthru support

From: Avi Kivity <avi@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>,
	Rusty Russell <rusty@rustcorp.com.au>,
	qemu-devel@nongnu.org, kvm@vger.kernel.org,
	Hannes Reinecke <hare@suse.de>
Subject: Re: [PATCH] virtio-blk: add SGI_IO passthru support
Date: Mon, 27 Apr 2009 12:15:31 +0300	[thread overview]
Message-ID: <49F577B3.5050706@redhat.com> (raw)
In-Reply-To: <20090427082914.GA383@lst.de>

Christoph Hellwig wrote:
> [had the qemu list address wrong the first time, reply to this message,
>  not the previous if you were on Cc]
>
>
> Add support for SG_IO passthru (packet commands) to the virtio-blk
> backend.  Conceptually based on an older patch from Hannes Reinecke
> but largely rewritten to match the code structure and layering in
> virtio-blk.
>
> Note that currently we issue the hose SG_IO synchronously.  We could
> easily switch to async I/O, but that would required either bloating
> the VirtIOBlockReq by the size of struct sg_io_hdr or an additional
> memory allocation for each SG_IO request.
>   

I think that's worthwhile.  The extra bloat is trivial (especially as 
the number of inflight virtio requests is tightly bounded), and stalling 
the vcpu for requests is a pain.

-- 
error compiling committee.c: too many arguments to function