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Date: Thu, 13 Jan 2011 15:08:51 +0100
From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: [Qemu-devel] Re: [PATCH 3/5] iohandlers: Allow each iohandler to be
 enabled/disabled individually
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To: Amit Shah <amit.shah@redhat.com>
Cc: qemu list <qemu-devel@nongnu.org>, Paul Brook <paul@codesourcery.com>

On 01/13/11 15:00, Amit Shah wrote:
> On (Thu) Jan 13 2011 [14:55:25], Gerd Hoffmann wrote:
>> On 01/13/11 14:00, Amit Shah wrote:
>>>   {
>>> -    return assign_fd_handlers(fd, fd_read_poll, fd_read, fd_write, opaque);
>>> +    assign_fd_handlers(fd, fd_read_poll, fd_read, fd_write, opaque);
>>> +    set_read_poll_fd_action(fd, true);
>>> +    set_read_fd_action(fd, true);
>>> +    set_write_fd_action(fd, true);
>>> +    return 0;
>>>   }
>>
>> I'd suggest to move the *action calls into assign_fd_handlers() so
>> the handlers default to being enabled in all cases.  This should
>> match what most users need and thus minimize the number of *_action
>> calls needed.
>
> What may happen with that is the fd may get select()-ed for an operation
> that it didn't want to be put on the queue for.

I can't see such a race window given that most qemu code runs serialized 
anyway.  If you call assign_fd_handlers() + set_write_fd_action(false) 
in sequence I can't see how a select call can happen inbetween ...

cheers,
   Gerd