virtio-blk: advertise F_WCE (F_FLUSH) if F_CONFIG_WCE is advertised

Virtio spec 1.1 (and earlier), 5.2.5.2 Driver Requirements: Device
Initialization:

"Devices SHOULD always offer VIRTIO_BLK_F_FLUSH, and MUST offer it if
they offer VIRTIO_BLK_F_CONFIG_WCE"

Currently F_CONFIG_WCE and F_WCE are not connected to each other.
Qemu will advertise F_CONFIG_WCE if config-wce argument is
set for virtio-blk device. And F_WCE is advertised only if
underlying block backend actually has it's caching enabled.

Fix this by advertising F_WCE if F_CONFIG_WCE is also advertised.

To preserve backwards compatibility with newer machine types make this
behaviour governed by "x-enable-wce-if-config-wce" virtio-blk-device
property and introduce hw_compat_4_2 with new property being off by
default for all machine types <= 4.2 (but don't introduce 4.3
machine type itself yet).

Signed-off-by: Evgeny Yakovlev <wrfsh@yandex-team.ru>
Message-Id: <1572978137-189218-1-git-send-email-wrfsh@yandex-team.ru>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/hw/core/machine.c b/hw/core/machine.c
index 1689ad3bf8..023548b4f3 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -27,6 +27,11 @@
 #include "hw/pci/pci.h"
 #include "hw/mem/nvdimm.h"
 
+GlobalProperty hw_compat_4_2[] = {
+    { "virtio-blk-device", "x-enable-wce-if-config-wce", "off" },
+};
+const size_t hw_compat_4_2_len = G_N_ELEMENTS(hw_compat_4_2);
+
 GlobalProperty hw_compat_4_1[] = {
     { "virtio-pci", "x-pcie-flr-init", "off" },
 };