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Date: Sat, 07 Jun 2014 21:27:26 +0200
From: Max Reitz <mreitz@redhat.com>
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Subject: Re: [Qemu-devel] [RFC 3/5] nbd: Use aio_set_fd_handler2()
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To: Paolo Bonzini <pbonzini@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <famz@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

On 06.06.2014 09:44, Paolo Bonzini wrote:
> Il 05/06/2014 20:18, Max Reitz ha scritto:
>>>
>>> Why is this design cleaner?  Because NBD code doesn't have to worry
>>> about fd handlers.  It uses straightforward coroutine send/recv for
>>> socket I/O inside nbd_read_req() and nbd_write_resp().  It's easy to 
>>> see
>>> that only one coroutine receives from the socket and that only one
>>> coroutine writes to the socket.
>>
>> Yes, this sounds better. I'll take a look into it and see how far I can
>> get.
>
> But it doesn't solve any problem, and requires rethinking the 
> aio_set_fd_handler API.

It might clean things up. :-)

On the other hand, you are right, it's probably too complicated right now.

> I suggest you just refactor all calls to qemu_set_fd_handler2 into a 
> function like
>
>     qemu_set_fd_handler2(fd, NULL,
>                  nbd_can_read(client) ? nbd_read : NULL,
>                  client->send_coroutine ?
>                     nbd_restart_write : NULL,
>                  opaque);
>
> and call this function every time the result of nbd_can_read() 
> changes.  Then you can switch to aio_set_fd_handler easily.

Seems good, I'll do that.

Max