Re: [Qemu-devel] Re: [PATCH 13/21] dma-helpers: replace bdrv_aio_writev() with bdrv_aio_writev_proxy().

Kevin Wolf
2010-11-29T09:52:37Z

Am 28.11.2010 12:55, schrieb Yoshiaki Tamura:
> 2010/11/28 Michael S. Tsirkin <mst@redhat.com>:
>> On Thu, Nov 25, 2010 at 03:06:52PM +0900, Yoshiaki Tamura wrote:
>>> Replace bdrv_aio_writev() with bdrv_aio_writev_proxy() to let
>>> event-tap capture events from dma-helpers.
>>>
>>> Signed-off-by: Yoshiaki Tamura <tamura.yoshiaki@lab.ntt.co.jp>
>>
>> Same comment as -net here: it's not clear when should
>> a device use bdrv_aio_writev_proxy and when bdrv_aio_writev.
>> If all devices should just use _proxy, let's
>> just make bdrv_aio_writev DTRT instead.
>
> Same as I replied to the net layer question. However, I had
> troubles with inserting event-tap functions into block.c before.
> block.c gets linked with utils like qemu-img, but they don't get
> linked with emulators code which event-tap uses in it. So I want
> to avoid linking block and event-tap for utils, but I guess we
> don't want to use ifdefs for this. I'm wondering how I can solve
> this problem cleanly.
>
> Kevin, do you have suggestions here?

Michael's stubs (probably in qemu-tool.c) seem to be the right solution.

Which requests do you actually want to intercept? I assume you're aware
that for example qcow2 internally calls another bdrv_aio_readv/writev
that accesses the image file.

So if you only want to have the requests that come directly from
devices, maybe you'll have to restrict it to BlockDriverStates that
belongs to a drive. I think this is the case if it has a non-empty
device name.

Kevin