virtio: introduce VirtIOConfigSizeParams & virtio_get_config_size

This is the first step towards moving all device config size calculation
logic into the virtio core code. In particular, this adds a struct that
contains all the necessary information for common virtio code to be able
to calculate the final config size for a device. This is expected to be
used with the new virtio_get_config_size helper, which calculates the
final length based on the provided host features.

This builds on top of already existing code like VirtIOFeature and
virtio_feature_get_config_size(), but adds additional fields, as well as
sanity checking so that device-specifc code doesn't have to duplicate it.

An example usage would be:

    static const VirtIOFeature dev_features[] = {
        {.flags = 1ULL << FEATURE_1_BIT,
         .end = endof(struct virtio_dev_config, feature_1)},
        {.flags = 1ULL << FEATURE_2_BIT,
         .end = endof(struct virtio_dev_config, feature_2)},
        {}
    };

    static const VirtIOConfigSizeParams dev_cfg_size_params = {
        .min_size = DEV_BASE_CONFIG_SIZE,
        .max_size = sizeof(struct virtio_dev_config),
        .feature_sizes = dev_features
    };

    // code inside my_dev_device_realize()
    size_t config_size = virtio_get_config_size(&dev_cfg_size_params,
                                                host_features);
    virtio_init(vdev, VIRTIO_ID_MYDEV, config_size);

Currently every device is expected to write its own boilerplate from the
example above in device_realize(), however, the next step of this
transition is moving VirtIOConfigSizeParams into VirtioDeviceClass,
so that it can be done automatically by the virtio initialization code.

All of the users of virtio_feature_get_config_size have been converted
to use virtio_get_config_size so it's no longer needed and is removed
with this commit.

Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
Message-Id: <20220906073111.353245-2-d-tatianin@yandex-team.ru>
Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/block/virtio-blk.c

@@ -49,13 +49,11 @@ static const VirtIOFeature feature_sizes[] = {
     {}
 };
 
-static void virtio_blk_set_config_size(VirtIOBlock *s, uint64_t host_features)
-{
-    s->config_size = MAX(VIRTIO_BLK_CFG_SIZE,
-        virtio_feature_get_config_size(feature_sizes, host_features));
-
-    assert(s->config_size <= sizeof(struct virtio_blk_config));
-}
+static const VirtIOConfigSizeParams cfg_size_params = {
+    .min_size = VIRTIO_BLK_CFG_SIZE,
+    .max_size = sizeof(struct virtio_blk_config),
+    .feature_sizes = feature_sizes
+};
 
 static void virtio_blk_init_request(VirtIOBlock *s, VirtQueue *vq,
                                     VirtIOBlockReq *req)
@@ -1204,8 +1202,8 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
         return;
     }
 
-    virtio_blk_set_config_size(s, s->host_features);
-
+    s->config_size = virtio_get_config_size(&cfg_size_params,
+                                            s->host_features);
     virtio_init(vdev, VIRTIO_ID_BLOCK, s->config_size);
 
     s->blk = conf->conf.blk;

hw/net/virtio-net.c

@@ -106,6 +106,12 @@ static const VirtIOFeature feature_sizes[] = {
     {}
 };
 
+static const VirtIOConfigSizeParams cfg_size_params = {
+    .min_size = endof(struct virtio_net_config, mac),
+    .max_size = sizeof(struct virtio_net_config),
+    .feature_sizes = feature_sizes
+};
+
 static VirtIONetQueue *virtio_net_get_subqueue(NetClientState *nc)
 {
     VirtIONet *n = qemu_get_nic_opaque(nc);
@@ -3241,8 +3247,7 @@ static void virtio_net_set_config_size(VirtIONet *n, uint64_t host_features)
 {
     virtio_add_feature(&host_features, VIRTIO_NET_F_MAC);
 
-    n->config_size = virtio_feature_get_config_size(feature_sizes,
-                                                    host_features);
+    n->config_size = virtio_get_config_size(&cfg_size_params, host_features);
 }
 
 void virtio_net_set_netclient_name(VirtIONet *n, const char *name,

hw/virtio/virtio.c

@@ -3006,11 +3006,12 @@ int virtio_set_features(VirtIODevice *vdev, uint64_t val)
     return ret;
 }
 
-size_t virtio_feature_get_config_size(const VirtIOFeature *feature_sizes,
-                                      uint64_t host_features)
+size_t virtio_get_config_size(const VirtIOConfigSizeParams *params,
+                              uint64_t host_features)
 {
-    size_t config_size = 0;
-    int i;
+    size_t config_size = params->min_size;
+    const VirtIOFeature *feature_sizes = params->feature_sizes;
+    size_t i;
 
     for (i = 0; feature_sizes[i].flags != 0; i++) {
         if (host_features & feature_sizes[i].flags) {
@@ -3018,6 +3019,7 @@ size_t virtio_feature_get_config_size(const VirtIOFeature *feature_sizes,
         }
     }
 
+    assert(config_size <= params->max_size);
     return config_size;
 }
 

include/hw/virtio/virtio.h

@@ -49,8 +49,14 @@ typedef struct VirtIOFeature {
     size_t end;
 } VirtIOFeature;
 
-size_t virtio_feature_get_config_size(const VirtIOFeature *features,
-                                      uint64_t host_features);
+typedef struct VirtIOConfigSizeParams {
+    size_t min_size;
+    size_t max_size;
+    const VirtIOFeature *feature_sizes;
+} VirtIOConfigSizeParams;
+
+size_t virtio_get_config_size(const VirtIOConfigSizeParams *params,
+                              uint64_t host_features);
 
 typedef struct VirtQueue VirtQueue;