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Date: Wed, 10 Dec 2008 12:50:17 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [RFC] Replace posix-aio with custom thread pool
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To: Gerd Hoffmann <kraxel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>, qemu-devel@nongnu.org, kvm-devel <kvm@vger.kernel.org>

Gerd Hoffmann wrote:
>>> To solve this in userland without kernel aio we'd need to open (not
>>> just dup)
>>>       
>> Why not just dup?  I've implemented this and it seems to work.
>>     
>
> unix keeps the file pointer in the (global) file table.  The
> (per-process) file descriptor table references the file table.
>
> opening twice gives you two file descriptor table entries referencing
> two file table entries.  duping gives you two file descriptors
> referencing the *same* file table entry.  Thus the two fds share the
> file pointer.
>   

But opening twice means that you lose coherency with NFS.

I hate Unix.

Regards,

Anthony Liguori

> HTH,
>   Gerd
>
>
>