virtio: core support for config generation
virtio 1.0 spec says:
Drivers MUST NOT assume reads from fields greater than 32 bits wide are
atomic, nor are reads from multiple fields: drivers SHOULD read device
configuration space fields like so:
u32 before, after;
do {
before = get_config_generation(device);
// read config entry/entries.
after = get_config_generation(device);
} while (after != before);
Do exactly this, for transports that support it.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index a61cd37..ca3ed78 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -19,6 +19,9 @@
* offset: the offset of the configuration field
* buf: the buffer to read the field value from.
* len: the length of the buffer
+ * @generation: config generation counter
+ * vdev: the virtio_device
+ * Returns the config generation counter
* @get_status: read the status byte
* vdev: the virtio_device
* Returns the status byte
@@ -60,6 +63,7 @@
void *buf, unsigned len);
void (*set)(struct virtio_device *vdev, unsigned offset,
const void *buf, unsigned len);
+ u32 (*generation)(struct virtio_device *vdev);
u8 (*get_status)(struct virtio_device *vdev);
void (*set_status)(struct virtio_device *vdev, u8 status);
void (*reset)(struct virtio_device *vdev);
@@ -301,14 +305,33 @@
return ret;
}
+/* Read @count fields, @bytes each. */
+static inline void __virtio_cread_many(struct virtio_device *vdev,
+ unsigned int offset,
+ void *buf, size_t count, size_t bytes)
+{
+ u32 old, gen = vdev->config->generation ?
+ vdev->config->generation(vdev) : 0;
+ int i;
+
+ do {
+ old = gen;
+
+ for (i = 0; i < count; i++)
+ vdev->config->get(vdev, offset + bytes * i,
+ buf + i * bytes, bytes);
+
+ gen = vdev->config->generation ?
+ vdev->config->generation(vdev) : 0;
+ } while (gen != old);
+}
+
+
static inline void virtio_cread_bytes(struct virtio_device *vdev,
unsigned int offset,
void *buf, size_t len)
{
- int i;
-
- for (i = 0; i < len; i++)
- vdev->config->get(vdev, offset + i, buf + i, 1);
+ __virtio_cread_many(vdev, offset, buf, len, 1);
}
static inline void virtio_cwrite8(struct virtio_device *vdev,
@@ -352,6 +375,7 @@
{
u64 ret;
vdev->config->get(vdev, offset, &ret, sizeof(ret));
+ __virtio_cread_many(vdev, offset, &ret, 1, sizeof(ret));
return virtio64_to_cpu(vdev, (__force __virtio64)ret);
}