[PATCH 08/16] virtio_ring: virtqueue_add_outbuf / virtqueue_add_inbuf.

[Rusty Russell]

These are specialized versions of virtqueue_add_buf(), which cover
over 50% of cases and are far clearer.

In particular, the scatterlists passed to these functions don't have
to be clean (ie. we ignore end markers).

FIXME: I'm not sure about the unclean sglist bit.  I had a more
ambitious one which conditionally ignored end markers in the iterator,
but it was ugly and I suspect this is just as fast.  Maybe we should
just fix all the drivers?

Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
---
 drivers/virtio/virtio_ring.c |   58 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/virtio.h       |   10 ++++++++
 2 files changed, 68 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index c537385..fb282b5 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -345,6 +345,64 @@ int virtqueue_add_sgs(struct virtqueue *_vq,
 EXPORT_SYMBOL_GPL(virtqueue_add_sgs);
 
 /**
+ * virtqueue_add_outbuf - expose output buffers to other end
+ * @vq: the struct virtqueue we're talking about.
+ * @sgs: array of scatterlists (need not be terminated!)
+ * @num: the number of scatterlists readable by other side
+ * @data: the token identifying the buffer.
+ * @gfp: how to do memory allocations (if necessary).
+ *
+ * Caller must ensure we don't call this with other virtqueue operations
+ * at the same time (except where noted).
+ *
+ * Returns zero or a negative error (ie. ENOSPC, ENOMEM).
+ */
+int virtqueue_add_outbuf(struct virtqueue *vq,
+			 struct scatterlist sg[], unsigned int num,
+			 void *data,
+			 gfp_t gfp)
+{
+	unsigned int i;
+
+	/* We're about to iterate, so this is pretty cheap. */
+	for (i = 0; i < num - 1; i++)
+		sg_unmark_end(sg + i);
+	sg_mark_end(sg + i);
+
+	return virtqueue_add(vq, &sg, num, 1, 0, data, gfp);
+}
+EXPORT_SYMBOL_GPL(virtqueue_add_outbuf);
+
+/**
+ * virtqueue_add_inbuf - expose input buffers to other end
+ * @vq: the struct virtqueue we're talking about.
+ * @sgs: array of scatterlists (need not be terminated!)
+ * @num: the number of scatterlists writable by other side
+ * @data: the token identifying the buffer.
+ * @gfp: how to do memory allocations (if necessary).
+ *
+ * Caller must ensure we don't call this with other virtqueue operations
+ * at the same time (except where noted).
+ *
+ * Returns zero or a negative error (ie. ENOSPC, ENOMEM).
+ */
+int virtqueue_add_inbuf(struct virtqueue *vq,
+			struct scatterlist sg[], unsigned int num,
+			void *data,
+			gfp_t gfp)
+{
+	unsigned int i;
+
+	/* We're about to iterate, so this is pretty cheap. */
+	for (i = 0; i < num - 1; i++)
+		sg_unmark_end(sg + i);
+	sg_mark_end(sg + i);
+
+	return virtqueue_add(vq, &sg, num, 0, 1, data, gfp);
+}
+EXPORT_SYMBOL_GPL(virtqueue_add_inbuf);
+
+/**
  * virtqueue_kick_prepare - first half of split virtqueue_kick call.
  * @vq: the struct virtqueue
  *
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 6eff15b..b442500 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -40,6 +40,16 @@ int virtqueue_add_buf(struct virtqueue *vq,
 		      void *data,
 		      gfp_t gfp);
 
+int virtqueue_add_outbuf(struct virtqueue *vq,
+			 struct scatterlist sg[], unsigned int num,
+			 void *data,
+			 gfp_t gfp);
+
+int virtqueue_add_inbuf(struct virtqueue *vq,
+			struct scatterlist sg[], unsigned int num,
+			void *data,
+			gfp_t gfp);
+
 int virtqueue_add_sgs(struct virtqueue *vq,
 		      struct scatterlist *sgs[],
 		      unsigned int out_sgs,
-- 
1.7.10.4

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