Linux Virtualization - Nov 2009 - [PATCHv4 1/6] qemu/virtio: move features to an inline function

devices should have the final say over which virtio features they
support. E.g. indirect entries may or may not make sense in the context
of virtio-console. In particular, for vhost, we do not want to report to
guest bits not supported by kernel backend.  Move the common bits from
virtio-pci to an inline function and let each device call it.

No functional changes.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 hw/virtio-balloon.c |    2 +-
 hw/virtio-blk.c     |    2 +-
 hw/virtio-console.c |    2 +-
 hw/virtio-net.c     |    2 +-
 hw/virtio-pci.c     |    3 ---
 hw/virtio.h         |   10 ++++++++++
 6 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/hw/virtio-balloon.c b/hw/virtio-balloon.c
index 7ca783e..15b50bb 100644
--- a/hw/virtio-balloon.c
+++ b/hw/virtio-balloon.c
@@ -127,7 +127,7 @@ static void virtio_balloon_set_config(VirtIODevice *vdev,
 
 static uint32_t virtio_balloon_get_features(VirtIODevice *vdev)
 {
-    return 0;
+    return virtio_common_features();
 }
 
 static ram_addr_t virtio_balloon_to_target(void *opaque, ram_addr_t target)
diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
index 2630b99..db727b9 100644
--- a/hw/virtio-blk.c
+++ b/hw/virtio-blk.c
@@ -445,7 +445,7 @@ static uint32_t virtio_blk_get_features(VirtIODevice *vdev)
     if (strcmp(s->serial_str, "0"))
         features |= 1 << VIRTIO_BLK_F_IDENTIFY;
 
-    return features;
+    return features | virtio_common_features();
 }
 
 static void virtio_blk_save(QEMUFile *f, void *opaque)
diff --git a/hw/virtio-console.c b/hw/virtio-console.c
index 92c953c..79544bb 100644
--- a/hw/virtio-console.c
+++ b/hw/virtio-console.c
@@ -53,7 +53,7 @@ static void virtio_console_handle_input(VirtIODevice *vdev,
VirtQueue *vq)
 
 static uint32_t virtio_console_get_features(VirtIODevice *vdev)
 {
-    return 0;
+    return virtio_common_features();
 }
 
 static int vcon_can_read(void *opaque)
diff --git a/hw/virtio-net.c b/hw/virtio-net.c
index ce8e6cb..469c6e3 100644
--- a/hw/virtio-net.c
+++ b/hw/virtio-net.c
@@ -154,7 +154,7 @@ static uint32_t virtio_net_get_features(VirtIODevice *vdev)
     }
 #endif
 
-    return features;
+    return features | virtio_common_features();
 }
 
 static uint32_t virtio_net_bad_features(VirtIODevice *vdev)
diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
index 01782e5..0716f6f 100644
--- a/hw/virtio-pci.c
+++ b/hw/virtio-pci.c
@@ -230,9 +230,6 @@ static uint32_t virtio_ioport_read(VirtIOPCIProxy *proxy,
uint32_t addr)
     switch (addr) {
     case VIRTIO_PCI_HOST_FEATURES:
         ret = vdev->get_features(vdev);
-        ret |= (1 << VIRTIO_F_NOTIFY_ON_EMPTY);
-        ret |= (1 << VIRTIO_RING_F_INDIRECT_DESC);
-        ret |= (1 << VIRTIO_F_BAD_FEATURE);
         break;
     case VIRTIO_PCI_GUEST_FEATURES:
         ret = vdev->features;
diff --git a/hw/virtio.h b/hw/virtio.h
index 0f9be7d..799e608 100644
--- a/hw/virtio.h
+++ b/hw/virtio.h
@@ -167,4 +167,14 @@ VirtIODevice *virtio_net_init(DeviceState *dev);
 VirtIODevice *virtio_console_init(DeviceState *dev);
 VirtIODevice *virtio_balloon_init(DeviceState *dev);
 
+static inline uint32_t virtio_common_features(void)
+{
+    uint32_t features = 0;
+    features |= (1 << VIRTIO_F_NOTIFY_ON_EMPTY);
+    features |= (1 << VIRTIO_RING_F_INDIRECT_DESC);
+    features |= (1 << VIRTIO_F_BAD_FEATURE);
+
+    return features;
+}
+
 #endif
-- 
1.6.5.2.143.g8cc62

Michael S. Tsirkin wrote:
> devices should have the final say over which virtio features they
> support. E.g. indirect entries may or may not make sense in the context
> of virtio-console. In particular, for vhost, we do not want to report to
> guest bits not supported by kernel backend.  Move the common bits from
> virtio-pci to an inline function and let each device call it.
>
> No functional changes.
>   
This is a layering violation.  There are transport specific features and 
device specific features.  The virtio-net device should have no 
knowledge or nack'ing ability for transport features.

If you need to change transport features, it suggests you're modeling 
things incorrectly and should be supplying an alternative transport 
implementation.

Regards,

Anthony Liguori