virtio: console: Introduce a send_buf function for a common path for sending data to host

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@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 33 insertions, 17 deletions

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 5096d92f5b89..d01051060be3 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -233,6 +233,38 @@ static bool port_has_data(struct port *port)
         return ret;
 }
 
+static ssize_t send_buf(struct port *port, void *in_buf, size_t in_count)
+{
+        struct scatterlist sg[1];
+        struct virtqueue *out_vq;
+        ssize_t ret;
+        unsigned int len;
+
+        out_vq = port->out_vq;
+
+        sg_init_one(sg, in_buf, in_count);
+        ret = out_vq->vq_ops->add_buf(out_vq, sg, 1, 0, in_buf);
+
+        /* Tell Host to go! */
+        out_vq->vq_ops->kick(out_vq);
+
+        if (ret < 0) {
+                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, &len))
+                cpu_relax();
+fail:
+        /* We're expected to return the amount of data we wrote */
+        return len;
+}
+
 /*
  * Give out the data that's requested from the buffer that we have
  * queued up.
@@ -280,10 +312,7 @@ 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 +321,7 @@ 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, (void *)buf, count);
 }
 
 /*