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

[Blue Swirl <blauwirbel@gmail.com>]

On Sun, Sep 27, 2009 at 5:24 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> On Sun, Sep 27, 2009 at 04:21:29PM +0200, Michael S. Tsirkin wrote:
>> On Sun, Sep 27, 2009 at 04:14:49PM +0200, Avi Kivity wrote:
>> > On 09/27/2009 04:08 PM, Michael S. Tsirkin wrote:
>> >>
>> >>
>> >>>> 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.
>> >>>
>> >> Doesn't naming it target_page_align32 address this concern?
>> >>
>> >
>> > How can the caller (except in your special case) know if it has a
>> > quantity that will fit in 32 bits?
>>
>> It's actually not unusual for devices to limit addressing to 32 bit, whatever
>> the bus supports.
>
> I would say that devices normally have a specific addressing, and should
> not be using target specific types at all.  This alignment to target
> page size is actually an unusual thing.

Actually, AFAICT MSI-X spec (6.8.2, from the MSI entry in Wikipedia)
only requires a QWORD alignment. There is some blurb about 4k
alignment, but I think it only describes how software should use the
structure. If this is the case, we could drop the whole target page
stuff.