Re: [PATCH 5/9] KVM: Adds ability to signal userspace using a file-descriptor

["Gregory Haskins" <ghaskins-Et1tbQHTxzrQT0dZR+AlfA@public.gmane.org>]

>>> On Tue, May 15, 2007 at 11:40 AM, in message
<Pine.LNX.4.64.0705150832130.30085-GPJ85BhbkB8RepQJljzAVbITYcZ0+W3JAL8bYrjMMd8@public.gmane.org>, Davide Libenzi
<davidel-AhlLAIvw+VEjIGhXcJzhZg@public.gmane.org> wrote: 
>
> I don't know how critical is the path where you will be doing check. The 
> eventfd_fget() is pretty fast, so if you're not looking at a performance 
> critical path, I'd suggest that. Otherwise you can do an early 
> eventfd_get, and keep the file*. If you have no the ways to know if the 
> userspace disconnected, an atomic_read(&file- >f_count)==1 will tell you 
> that you're the only owner of the file* (that is, userspace closed the 
> eventfd descriptor). I'd give preference to the former option though.

Thanks for the insight, Davide.  It sounds like we can probably stay with the way I have it for now, and keep the file->f_count idea in our back pocket should a performance problem arise.

> Avi, as you may have read from lkml, Andrew prefers the eventfd symbols 
> export to come through the kvm tree, since they do not want to export 
> symbols that so far has no module users.

I can create a patch and add it to my series for this work.

Thanks again,
-Greg


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