hwrng: virtio-rng - Convert to new API

This patch converts virtio-rng to the new hw_rng API.

In the process it fixes a previously untriggered buffering bug where the
buffer is not drained correctly if it has a non-multiple-of-4 length.

Performance has improved under qemu-kvm testing also.

Signed-off-by: Ian Molton <ian.molton@collabora.co.uk>
Acked-by: Matt Mackall <mpm@selenic.com>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 27 insertions, 51 deletions

diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
index 915157fcff98..bdaef8e94021 100644
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -16,6 +16,7 @@
  *  along with this program; if not, write to the Free Software
  *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
  */
+
 #include <linux/err.h>
 #include <linux/hw_random.h>
 #include <linux/scatterlist.h>
@@ -23,78 +24,64 @@
 #include <linux/virtio.h>
 #include <linux/virtio_rng.h>
 
-/* The host will fill any buffer we give it with sweet, sweet randomness.  We
- * give it 64 bytes at a time, and the hwrng framework takes it 4 bytes at a
- * time. */
-#define RANDOM_DATA_SIZE 64
-
 static struct virtqueue *vq;
-static u32 *random_data;
-static unsigned int data_left;
+static unsigned int data_avail;
 static DECLARE_COMPLETION(have_data);
+static bool busy;
 
 static void random_recv_done(struct virtqueue *vq)
 {
-        unsigned int len;
-
         /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
-        if (!vq->vq_ops->get_buf(vq, &len))
+        if (!vq->vq_ops->get_buf(vq, &data_avail))
                 return;
 
-        data_left += len;
         complete(&have_data);
 }
 
-static void register_buffer(void)
+/* The host will fill any buffer we give it with sweet, sweet randomness. */
+static void register_buffer(u8 *buf, size_t size)
 {
         struct scatterlist sg;
 
-        sg_init_one(&sg, random_data+data_left, RANDOM_DATA_SIZE-data_left);
+        sg_init_one(&sg, buf, size);
+
         /* There should always be room for one buffer. */
-        if (vq->vq_ops->add_buf(vq, &sg, 0, 1, random_data) < 0)
+        if (vq->vq_ops->add_buf(vq, &sg, 0, 1, buf) < 0)
                 BUG();
+
         vq->vq_ops->kick(vq);
 }
 
-/* At least we don't udelay() in a loop like some other drivers. */
-static int virtio_data_present(struct hwrng *rng, int wait)
+static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
 {
-        if (data_left >= sizeof(u32))
-                return 1;
 
-again:
+        if (!busy) {
+                busy = true;
+                init_completion(&have_data);
+                register_buffer(buf, size);
+        }
+
         if (!wait)
                 return 0;
 
         wait_for_completion(&have_data);
 
-        /* Not enough?  Re-register. */
-        if (unlikely(data_left < sizeof(u32))) {
-                register_buffer();
-                goto again;
-        }
+        busy = false;
 
-        return 1;
+        return data_avail;
 }
 
-/* virtio_data_present() must have succeeded before this is called. */
-static int virtio_data_read(struct hwrng *rng, u32 *data)
+static void virtio_cleanup(struct hwrng *rng)
 {
-        BUG_ON(data_left < sizeof(u32));
-        data_left -= sizeof(u32);
-        *data = random_data[data_left / 4];
-
-        if (data_left < sizeof(u32)) {
-                init_completion(&have_data);
-                register_buffer();
-        }
-        return sizeof(*data);
+        if (busy)
+                wait_for_completion(&have_data);
 }
 
+
 static struct hwrng virtio_hwrng = {
-        .name = "virtio",
-        .data_present = virtio_data_present,
-        .data_read = virtio_data_read,
+        .name           = "virtio",
+        .cleanup        = virtio_cleanup,
+        .read           = virtio_read,
 };
 
 static int virtrng_probe(struct virtio_device *vdev)
@@ -112,7 +99,6 @@ static int virtrng_probe(struct virtio_device *vdev)
                 return err;
         }
 
-        register_buffer();
         return 0;
 }
 
@@ -138,21 +124,11 @@ static struct virtio_driver virtio_rng = {
 
 static int __init init(void)
 {
-        int err;
-
-        random_data = kmalloc(RANDOM_DATA_SIZE, GFP_KERNEL);
-        if (!random_data)
-                return -ENOMEM;
-
-        err = register_virtio_driver(&virtio_rng);
-        if (err)
-                kfree(random_data);
-        return err;
+        return register_virtio_driver(&virtio_rng);
 }
 
 static void __exit fini(void)
 {
-        kfree(random_data);
         unregister_virtio_driver(&virtio_rng);
 }
 module_init(init);