[PATCH 19/31] virtio: console: Introduce a send_buf function for a common path for sending data to host

[Amit Shah <amit.shah@xxxxxxxxxx>]

Adding support for generic ports that will write to userspace will need
some code changes.

Consolidate the write routine into send_buf() and put_chars() now just
calls into the new function.

Signed-off-by: Amit Shah <amit.shah@xxxxxxxxxx>
---
 drivers/char/virtio_console.c |   79 +++++++++++++++++++++++++++++++---------
 1 files changed, 61 insertions(+), 18 deletions(-)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 5096d92..9400b96 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -107,6 +107,9 @@ struct port {
 	 */
 	spinlock_t inbuf_lock;
 
+	/* Buffer that's used to pass data from the guest to the host */
+	struct port_buffer *outbuf;
+
 	/* The IO vqs for this port */
 	struct virtqueue *in_vq, *out_vq;
 
@@ -233,6 +236,55 @@ static bool port_has_data(struct port *port)
 	return ret;
 }
 
+static ssize_t send_buf(struct port *port, const char *in_buf, size_t in_count)
+{
+	struct scatterlist sg[1];
+	struct virtqueue *out_vq;
+	struct port_buffer *buf;
+	ssize_t ret;
+	unsigned int tmplen;
+
+	out_vq = port->out_vq;
+	buf = port->outbuf;
+
+	if (in_count > buf->size)
+		in_count = buf->size;
+
+	/*
+	 * Since we're not sure when the host will actually
+	 * consume the data and tell us about it, we have to
+	 * copy the data here in case the caller frees the
+	 * in_buf.
+	 */
+	memcpy(buf->buf, in_buf, in_count);
+
+	buf->len = in_count;
+
+	sg_init_one(sg, buf->buf, buf->len);
+	ret = out_vq->vq_ops->add_buf(out_vq, sg, 1, 0, buf);
+
+	/* Tell Host to go! */
+	out_vq->vq_ops->kick(out_vq);
+
+	if (ret < 0) {
+		buf->len = 0;
+		goto fail;
+	}
+
+	/*
+	 * Wait till the host acknowledges it pushed out the data we
+	 * sent. Also ensure we return to userspace the number of
+	 * bytes that were successfully consumed by the host.
+	 */
+	while (!out_vq->vq_ops->get_buf(out_vq, &tmplen))
+		cpu_relax();
+
+	buf->len = tmplen;
+fail:
+	/* We're expected to return the amount of data we wrote */
+	return buf->len;
+}
+
 /*
  * Give out the data that's requested from the buffer that we have
  * queued up.
@@ -280,10 +332,7 @@ static ssize_t fill_readbuf(struct port *port, char *out_buf, size_t out_count)
  */
 static int put_chars(u32 vtermno, const char *buf, int count)
 {
-	struct scatterlist sg[1];
 	struct port *port;
-	struct virtqueue *out_vq;
-	unsigned int len;
 
 	port = find_port_by_vtermno(vtermno);
 	if (!port)
@@ -292,20 +341,7 @@ static int put_chars(u32 vtermno, const char *buf, int count)
 	if (unlikely(early_put_chars))
 		return early_put_chars(vtermno, buf, count);
 
-	out_vq = port->out_vq;
-	/* This is a convenient routine to initialize a single-elem sg list */
-	sg_init_one(sg, buf, count);
-
-	/* This shouldn't fail: if it does, we lose chars. */
-	if (out_vq->vq_ops->add_buf(out_vq, sg, 1, 0, port) >= 0) {
-		/* Tell Host to go! */
-		out_vq->vq_ops->kick(out_vq);
-		while (!out_vq->vq_ops->get_buf(out_vq, &len))
-			cpu_relax();
-	}
-
-	/* We're expected to return the amount of data we wrote: all of it. */
-	return count;
+	return send_buf(port, buf, count);
 }
 
 /*
@@ -475,16 +511,23 @@ static int __devinit add_port(struct ports_device *portdev)
 		err = -ENOMEM;
 		goto free_port;
 	}
+	port->outbuf = alloc_buf(PAGE_SIZE);
+	if (!port->outbuf) {
+		err = -ENOMEM;
+		goto free_inbuf;
+	}
 
 	/* Register the input buffer the first time. */
 	add_inbuf(port->in_vq, inbuf);
 
 	err = init_port_console(port);
 	if (err)
-		goto free_inbuf;
+		goto free_outbuf;
 
 	return 0;
 
+free_outbuf:
+	free_buf(port->outbuf);
 free_inbuf:
 	free_buf(inbuf);
 free_port:
-- 
1.6.2.5

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