From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1MrsSm-0000Iw-Hw
	for qemu-devel@nongnu.org; Sun, 27 Sep 2009 08:02:48 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1MrsSi-0000IZ-5q
	for qemu-devel@nongnu.org; Sun, 27 Sep 2009 08:02:48 -0400
Received: from [199.232.76.173] (port=52363 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1MrsSh-0000IW-VW
	for qemu-devel@nongnu.org; Sun, 27 Sep 2009 08:02:43 -0400
Received: from mx1.redhat.com ([209.132.183.28]:38534)
	by monty-python.gnu.org with esmtp (Exim 4.60)
	(envelope-from <mst@redhat.com>) id 1MrsSh-0004Pn-27
	for qemu-devel@nongnu.org; Sun, 27 Sep 2009 08:02:43 -0400
Date: Sun, 27 Sep 2009 14:00:41 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [Qemu-devel] Re: [PATCHv2] qemu: target library, use it in msix
Message-ID: <20090927120041.GB24031@redhat.com>
References: <20090923200635.GA21246@redhat.com>
	<f43fc5580909241050jc8b82fbsb25eef096f8105eb@mail.gmail.com>
	<20090927082020.GA23513@redhat.com> <4ABF4110.80300@redhat.com>
	<20090927114459.GA24031@redhat.com> <4ABF52A5.5080409@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <4ABF52A5.5080409@redhat.com>
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: Blue Swirl <blauwirbel@gmail.com>, qemu-devel@nongnu.org

On Sun, Sep 27, 2009 at 01:55:17PM +0200, Avi Kivity wrote:
> On 09/27/2009 01:45 PM, Michael S. Tsirkin wrote:
>>
>>    
>>>> Thinking about this some more, this function just says "align a value to
>>>> page size". The value might not be a bus address at all, and indeed with
>>>> msix use, it is not. Makes sense?
>>>>
>>>>        
>>> In any case restricting it to unsigned invites truncation.
>>>      
>> If the value we are aligning fits in 32 bit, so does the aligned value.
>>    
>
> It's perfectly reasonable to call a such a function with a  
> target_ulong_t 

[mst@tuck qemu]$ grep -rIi target_ulong_t .
[mst@tuck qemu]$

?

> or target_phys_addr_t input and expect it to work.

Not if it's called target_page_align32 :)

>>>   We can have
>>>
>>>     target_phys_addr_t target_phys_page_align();
>>>     target_ulong_t target_virt_page_align();
>>>      
>> Right. And also
>>     target_page_align32();
>>     target_page_align64();
>>
>> We only use a 32 bit version now (passed value is a constant),
>> so I think I'll only implement it, and we'll add more when
>> they are used.
>>    
>
> How would the caller know what size argument they have?  They usually  
> have a target_phys_addr_t or a target_ulong_t.

In practice, the only user is now msix and it does not.  It has 0x1000
as a constant parameter.  For target_phys_addr_t users if we ever have
them, we'll just add target_phys_page_align. Generally it's unusual for
devices to care about size of target physical page.

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