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Subject[PATCH 2/2] virtio: Convert virtio-rng to the new API
Date
	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>
---
drivers/char/hw_random/virtio-rng.c | 79 ++++++++++++----------------------
1 files changed, 28 insertions(+), 51 deletions(-)
diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
index 915157f..76d00c4 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 +24,65 @@
#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 int busy;
+
+/* The host will fill any buffer we give it with sweet, sweet randomness. */

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)
+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 = 1;
+ 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 = 0;

- 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 +100,6 @@ static int virtrng_probe(struct virtio_device *vdev)
return err;
}

- register_buffer();
return 0;
}

@@ -138,21 +125,11 @@ 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);
--
1.6.5


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