[PATCH-for-6.0 1/3] hw/virtio: Add configure switch to disable legacy VIRTIO

[Philippe Mathieu-Daudé]

Per [1] (Terminology):

  Legacy interfaces are not required; ie. don’t implement them
  unless you have a need for backwards compatibility!

[2] (Version 1.0):

  The device configuration space uses the little-endian format
  for multi-byte fields.

and [3] (Legacy Interface):

  for legacy interfaces, device configuration space is generally
  the guest’s native endian, rather than PCI’s little-endian.
  The correct endian-ness is documented for each device.

Add the --disable-virtio-legacy configure flag to produce builds
with VIRTIO 1.0 only, and the --enable-virtio-legacy to include
legacy VIRTIO support (supporting legacy VIRTIO is the default).

[1] 
http://docs.oasis-open.org/virtio/virtio/v1.0/cs04/virtio-v1.0-cs04.html#x1-60001
[2] 
http://docs.oasis-open.org/virtio/virtio/v1.0/cs04/virtio-v1.0-cs04.html#x1-170003
[3] 
http://docs.oasis-open.org/virtio/virtio/v1.0/cs04/virtio-v1.0-cs04.html#x1-200003

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 configure                         | 10 ++++++++++
 meson.build                       |  1 +
 include/hw/virtio/virtio-access.h | 19 +++++--------------
 hw/virtio/virtio-legacy.c         | 29 +++++++++++++++++++++++++++++
 hw/virtio/meson.build             |  1 +
 5 files changed, 46 insertions(+), 14 deletions(-)
 create mode 100644 hw/virtio/virtio-legacy.c

diff --git a/configure b/configure
index 2c3c69f1188..f46216b3788 100755
--- a/configure
+++ b/configure
@@ -302,6 +302,7 @@ fdt="auto"
 netmap="no"
 sdl="auto"
 sdl_image="auto"
+virtio_legacy="enabled"
 virtiofsd="auto"
 virtfs=""
 libudev="auto"
@@ -1001,6 +1002,10 @@ for opt do
   ;;
   --enable-libudev) libudev="enabled"
   ;;
+  --disable-virtio-legacy) virtio_legacy="disabled"
+  ;;
+  --enable-virtio-legacy) virtio_legacy="enabled"
+  ;;
   --disable-virtiofsd) virtiofsd="disabled"
   ;;
   --enable-virtiofsd) virtiofsd="enabled"
@@ -1764,6 +1769,7 @@ disabled with --disable-FEATURE, default is enabled if 
available:
   vnc-png         PNG compression for VNC server
   cocoa           Cocoa UI (Mac OS X only)
   virtfs          VirtFS
+  virtio-legacy   enable support for legacy virtio (before VIRTIO 1.0)
   virtiofsd       build virtiofs daemon (virtiofsd)
   libudev         Use libudev to enumerate host devices
   mpath           Multipath persistent reservation passthrough
@@ -6816,6 +6822,10 @@ if test "$safe_stack" = "yes"; then
   echo "CONFIG_SAFESTACK=y" >> $config_host_mak
 fi
 
+if test "$virtio_legacy" = "enabled"; then
+  echo "CONFIG_VIRTIO_LEGACY=y" >> $config_host_mak
+fi
+
 # If we're using a separate build tree, set it up now.
 # DIRS are directories which we simply mkdir in the build tree;
 # LINKS are things to symlink back into the source tree
diff --git a/meson.build b/meson.build
index 39ac5cf6d8a..51406c28c6e 100644
--- a/meson.build
+++ b/meson.build
@@ -2061,6 +2061,7 @@
 summary_info += {'Block whitelist (rw)': 
config_host['CONFIG_BDRV_RW_WHITELIST']}
 summary_info += {'Block whitelist (ro)': 
config_host['CONFIG_BDRV_RO_WHITELIST']}
 summary_info += {'VirtFS support':    config_host.has_key('CONFIG_VIRTFS')}
+summary_info += {'Legacy VIRTIO support': 
config_host.has_key('CONFIG_VIRTIO_LEGACY')}
 summary_info += {'build virtiofs daemon': have_virtiofsd}
 summary_info += {'Multipath support': mpathpersist.found()}
 summary_info += {'VNC support':       vnc.found()}
diff --git a/include/hw/virtio/virtio-access.h 
b/include/hw/virtio/virtio-access.h
index 6818a23a2d3..b6c060f8cc6 100644
--- a/include/hw/virtio/virtio-access.h
+++ b/include/hw/virtio/virtio-access.h
@@ -20,24 +20,15 @@
 #include "hw/virtio/virtio.h"
 #include "hw/virtio/virtio-bus.h"
 
-#if defined(TARGET_PPC64) || defined(TARGET_ARM)
-#define LEGACY_VIRTIO_IS_BIENDIAN 1
-#endif
-
+#ifdef CONFIG_VIRTIO_LEGACY
+bool virtio_access_is_big_endian(VirtIODevice *vdev);
+#else
 static inline bool virtio_access_is_big_endian(VirtIODevice *vdev)
 {
-#if defined(LEGACY_VIRTIO_IS_BIENDIAN)
-    return virtio_is_big_endian(vdev);
-#elif defined(TARGET_WORDS_BIGENDIAN)
-    if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) {
-        /* Devices conforming to VIRTIO 1.0 or later are always LE. */
-        return false;
-    }
-    return true;
-#else
+    /* Devices conforming to VIRTIO 1.0 or later are always LE. */
     return false;
-#endif
 }
+#endif
 
 static inline uint16_t virtio_lduw_phys(VirtIODevice *vdev, hwaddr pa)
 {
diff --git a/hw/virtio/virtio-legacy.c b/hw/virtio/virtio-legacy.c
new file mode 100644
index 00000000000..bf28c824a25
--- /dev/null
+++ b/hw/virtio/virtio-legacy.c
@@ -0,0 +1,29 @@
+/*
+ * Legacy virtio endian helpers.
+ *
+ * Copyright Red Hat, Inc. 2020
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+#include "qemu/osdep.h"
+#include "hw/virtio/virtio.h"
+#include "hw/virtio/virtio-access.h"
+
+#if defined(TARGET_PPC64) || defined(TARGET_ARM)
+# define LEGACY_VIRTIO_IS_BIENDIAN 1
+#endif
+
+bool virtio_access_is_big_endian(VirtIODevice *vdev)
+{
+#if defined(LEGACY_VIRTIO_IS_BIENDIAN)
+    return virtio_is_big_endian(vdev);
+#elif defined(TARGET_WORDS_BIGENDIAN)
+    if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) {
+        /* Devices conforming to VIRTIO 1.0 or later are always LE. */
+        return false;
+    }
+    return true;
+#else
+    return false;
+#endif
+}
diff --git a/hw/virtio/meson.build b/hw/virtio/meson.build
index fbff9bc9d4d..95415913a9a 100644
--- a/hw/virtio/meson.build
+++ b/hw/virtio/meson.build
@@ -11,6 +11,7 @@
 
 virtio_ss = ss.source_set()
 virtio_ss.add(files('virtio.c'))
+virtio_ss.add(when: 'CONFIG_VIRTIO_LEGACY', if_true: files('virtio-legacy.c'))
 virtio_ss.add(when: 'CONFIG_VHOST', if_true: files('vhost.c', 
'vhost-backend.c'))
 virtio_ss.add(when: 'CONFIG_VHOST_USER', if_true: files('vhost-user.c'))
 virtio_ss.add(when: 'CONFIG_VHOST_VDPA', if_true: files('vhost-vdpa.c'))
-- 
2.26.2