From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1Nwu2M-0003MU-6Q
	for qemu-devel@nongnu.org; Wed, 31 Mar 2010 05:16:34 -0400
Received: from [140.186.70.92] (port=57653 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1Nwu2I-0003Kx-Dj
	for qemu-devel@nongnu.org; Wed, 31 Mar 2010 05:16:33 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69)
	(envelope-from <mst@redhat.com>) id 1Nwu2G-0000Qo-BG
	for qemu-devel@nongnu.org; Wed, 31 Mar 2010 05:16:30 -0400
Received: from mx1.redhat.com ([209.132.183.28]:18424)
	by eggs.gnu.org with esmtp (Exim 4.69)
	(envelope-from <mst@redhat.com>) id 1Nwu2G-0000QH-2I
	for qemu-devel@nongnu.org; Wed, 31 Mar 2010 05:16:28 -0400
Date: Wed, 31 Mar 2010 12:12:50 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
Message-ID: <20100331091250.GA31085@redhat.com>
References: <1269497376-21903-1-git-send-email-cam@cs.ualberta.ca>
	<4BAB30EE.4020509@redhat.com>
	<8286e4ee1003250924q7cca5e71u8b8b7c6d8b785eb8@mail.gmail.com>
	<4BAB90BB.5030401@redhat.com>
	<8286e4ee1003260914u5e6ceee2pf0c00590de182fb6@mail.gmail.com>
	<4BAE44F2.20801@redhat.com>
	<8286e4ee1003281248k204a5bd4tc48e6ccc755918b@mail.gmail.com>
	<4BB114AC.9040902@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <4BB114AC.9040902@redhat.com>
Subject: [Qemu-devel] Re: [PATCH v3 1/1] Shared memory uio_pci driver
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Avi Kivity <avi@redhat.com>
Cc: Cam Macdonell <cam@cs.ualberta.ca>, qemu-devel@nongnu.org, kvm@vger.kernel.org

On Mon, Mar 29, 2010 at 11:59:24PM +0300, Avi Kivity wrote:
> On 03/28/2010 10:48 PM, Cam Macdonell wrote:
>> On Sat, Mar 27, 2010 at 11:48 AM, Avi Kivity<avi@redhat.com>  wrote:
>>    
>>> On 03/26/2010 07:14 PM, Cam Macdonell wrote:
>>>      
>>>>        
>>>>> I'm not familiar with the uio internals, but for the interface, an
>>>>> ioctl()
>>>>> on the fd to assign an eventfd to an MSI vector.  Similar to ioeventfd,
>>>>> but
>>>>> instead of mapping a doorbell to an eventfd, it maps a real MSI to an
>>>>> eventfd.
>>>>>
>>>>>          
>>>> uio will never support ioctls.
>>>>        
>>> Why not?
>>>      
>> Perhaps I spoke too strongly, but it was rejected before
>>
>> http://thread.gmane.org/gmane.linux.kernel/756481
>>
>> With a compelling case perhaps it could be added.
>>    
>
> Ah, the usual "ioctls are ugly, go away".
>
> It could be done via sysfs:
>
>   $ cat /sys/.../msix/max-interrupts
>   256

This one can be discovered with existing sysfs.

>   $ echo 4 > /sys/.../msix/allocate
>   $ # subdirectories 0 1 2 3 magically appear
>   $ # bind fd 13 to msix

There's no way to know, when qemu starts, how many vectors will be used
by driver.  So I think we can just go ahead and allocate as many vectors
as supported by device at the moment when the first eventfd is bound.

>   $ echo 13 > /sys/.../msix/2/bind-fd

I think that this one can't work, both fd 13 and sysfs file will get
closed when /bin/echo process exits.

>   $ # from now on, msix interrupt 2 will call eventfd_signal() on fd 13
>
> Call me old fashioned, but I prefer ioctls.

I think we will have to use ioctl or irqcontrol because of lifetime
issues outlines above.

> -- 
> Do not meddle in the internals of kernels, for they are subtle and quick to panic.