Re: [Qemu-devel] [PATCH 10/17] s390x: keep hint on virtio managing size

[Aurelien Jarno <aurelien@aurel32.net>]

On Mon, Apr 18, 2011 at 11:03:59PM +0200, Alexander Graf wrote:
> 
> On 18.04.2011, at 21:06, Aurelien Jarno wrote:
> 
> > On Fri, Apr 15, 2011 at 05:32:51PM +0200, Alexander Graf wrote:
> >> The s390x virtio bus keeps management information on virtio after the top
> >> of the guest's RAM. We need to be able to tell the guest the size of its
> >> RAM (without virtio stuff), but also be able to trap when the guest accesses
> >> RAM outside of its scope (including virtio stuff).
> >> 
> >> So we need a variable telling us the size of the virtio stuff, so we can
> >> calculate the highest available RAM address from that.
> >> 
> >> While at it, also increase the maximum number of virtio pages, so we play
> >> along well with more recent kernels that spawn a ridiculous number of virtio
> >> console adapters.
> >> 
> >> Signed-off-by: Alexander Graf <agraf@suse.de>
> >> ---
> >> hw/s390-virtio-bus.c |    3 +++
> >> hw/s390-virtio-bus.h |    2 +-
> >> target-s390x/cpu.h   |    3 +++
> >> 3 files changed, 7 insertions(+), 1 deletions(-)
> >> 
> >> diff --git a/hw/s390-virtio-bus.c b/hw/s390-virtio-bus.c
> >> index bb49e39..a90963b 100644
> >> --- a/hw/s390-virtio-bus.c
> >> +++ b/hw/s390-virtio-bus.c
> >> @@ -60,6 +60,9 @@ static const VirtIOBindings virtio_s390_bindings;
> >> 
> >> static ram_addr_t s390_virtio_device_num_vq(VirtIOS390Device *dev);
> >> 
> >> +/* length of VirtIO device pages */
> >> +target_phys_addr_t virtio_size = S390_DEVICE_PAGES * TARGET_PAGE_SIZE;
> >> +
> > 
> > If this variable is never written, can it be declared const?
> 
> Does that improve anything for exported variables? Do they get put into a ro section then?
> 

Unfortunately, that will still be an exported variable, and it's a pitty
to use that just because we can't have a #define in hw/* included in
target-*/* . That said I just realized that a lot of target are actually
doing that, maybe it's the solution here.

Adding a const here will clearly show to people reading the code that
it's nothing more than advanced #define.


-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net