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Re: [Qemu-devel] eventfd_signal()

From: Paolo Bonzini
Subject: Re: [Qemu-devel] eventfd_signal()
Date: Fri, 08 May 2015 13:24:59 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0

On 08/05/2015 12:58, Catalin Vasile wrote:
> Is eventfd blocking? By that I mean: If I signal the guest for
> something, will that thread remain blocked till the guest clears the
> interrupt?

No.  If you want that, write 2^64-2 to the eventfd and do a

   pfd.fd = ...
   pfd.events = POLLOUT;
   poll(&pfd, 1, -1);

after the write.

With this algorithm, a write will fail with EINVAL if there is already
another pending write somewhere.  The "poll" will still work after the
failed write.


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