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Date: Sun, 27 Sep 2009 14:19:41 +0200
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [Qemu-devel] Re: [PATCHv2] qemu: target library, use it in msix
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Blue Swirl <blauwirbel@gmail.com>, qemu-devel@nongnu.org

On 09/27/2009 02:00 PM, Michael S. Tsirkin wrote:
> 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]$
>
> ?
>
>    

target_ulong.

>> or target_phys_addr_t input and expect it to work.
>>      
> Not if it's called target_page_align32 :)
>    

You generally don't know the size of quantities you align.

>> 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.
>    

I'd fill better with uint64_t, at least that won't truncate.

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