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, 8 insertions, 1 deletions

diff --git a/util/osdep.c b/util/osdep.c
index 80c6bfe..534b511 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -52,7 +52,14 @@ extern int madvise(caddr_t, size_t, int);
 
 static bool fips_enabled = false;
 
-static const char *hw_version = QEMU_VERSION;
+/* Starting on QEMU 2.5, qemu_hw_version() returns "2.5+" by default
+ * instead of QEMU_VERSION, so setting hw_version on MachineClass
+ * is no longer mandatory.
+ *
+ * Do NOT change this string, or it will break compatibility on all
+ * machine classes that don't set hw_version.
+ */
+static const char *hw_version = "2.5+";
 
 int socket_set_cork(int fd, int v)
 {