osdep: Change default value of qemu_hw_version() to "2.5+"

There are two issues with qemu_hw_version() today:

1) If a machine has hw_version set, the value returned by it is
   not very useful, because it is not the actual QEMU version.
2) If a machine does't set hw_version, the return value of
   qemu_hw_version() is broken, because it will change when
   upgrading QEMU.

For those reasons, using qemu_hw_version() is strongly
discouraged, and should be used only in code that used
QEMU_VERSION in the past and needs to keep compatibility.

To fix (2), instead of making every machine broken by default
unless they set hw_version, make qemu_hw_version() simply return
"2.5+" if qemu_set_hw_version() is not called.

Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/hw/boards.h b/include/hw/boards.h
index 24eb6f0e77..5da4fb00ee 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -51,6 +51,11 @@ bool machine_mem_merge(MachineState *machine);
  *    used to provide @cpu_index to socket number mapping, allowing
  *    a machine to group CPU threads belonging to the same socket/package
  *    Returns: socket number given cpu_index belongs to.
+ * @hw_version:
+ *    Value of QEMU_VERSION when the machine was added to QEMU.
+ *    Set only by old machines because they need to keep
+ *    compatibility on code that exposed QEMU_VERSION to guests in
+ *    the past (and now use qemu_hw_version()).
  */
 struct MachineClass {
     /*< private >*/