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Date: Fri, 06 Jun 2014 09:44:51 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [RFC 3/5] nbd: Use aio_set_fd_handler2()
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To: Max Reitz <mreitz@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>

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.  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.

Paolo