Re: [Qemu-devel] Re: [PATCHv2] qemu: target library, use it in msix

[Avi Kivity]

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
> >      
> address@hidden qemu]$ grep -rIi target_ulong_t .
> address@hidden 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.