On 2012/2/1,星期三 16:12, Amit Shah wrote:

Hi,

Sorry for the late reply.

On (Thu) 12 Jan 2012 [09:20:07], zanghongyong@huawei.com wrote:

quoted

From: Hongyong Zang<redacted>

Add setup_port_vq(). Create the io ports' vqs when add_port.

Can you describe the changes in more detail, please?

The motivation of this patch is as follows. When we use virtio-serial
for communication between guest and host, we usually use only a few
ports (for example 1 or 2 ports), so there's no need to create max ports
when build a virtio-serial. The patch does the port hot-plug thing without
port hot-unplug.

quoted

Signed-off-by: Hongyong Zang<redacted>
---
  drivers/char/virtio_console.c |   65 ++++++++++++++++++++++++++++++++++++++--
  1 files changed, 61 insertions(+), 4 deletions(-)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 8e3c46d..2e5187e 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c

@@ -1132,6 +1132,55 @@ static void send_sigio_to_port(struct port *port)
  		kill_fasync(&port->async_queue, SIGIO, POLL_OUT);
  }

+static void in_intr(struct virtqueue *vq);
+static void out_intr(struct virtqueue *vq);
+
+static int setup_port_vq(struct ports_device *portdev,  u32 id)
+{
+	int err, vq_num;
+	vq_callback_t **io_callbacks;
+	char **io_names;
+	struct virtqueue **vqs;
+	u32 i,j,nr_ports,nr_queues;
+
+	err = 0;
+	vq_num = (id + 1) * 2;
+	nr_ports = portdev->config.max_nr_ports;
+	nr_queues = use_multiport(portdev) ? (nr_ports + 1) * 2 : 2;
+
+	vqs = kmalloc(nr_queues * sizeof(struct virtqueue *), GFP_KERNEL);
+	io_callbacks = kmalloc(nr_queues * sizeof(vq_callback_t *), GFP_KERNEL);
+	io_names = kmalloc(nr_queues * sizeof(char *), GFP_KERNEL);
+	if (!vqs || !io_callbacks || !io_names) {
+		err = -ENOMEM;
+		goto free;
+	}
+
+	for (i = 0, j = 0; i<= nr_ports; i++) {
+		io_callbacks[j] = in_intr;
+		io_callbacks[j + 1] = out_intr;
+		io_names[j] = NULL;
+		io_names[j + 1] = NULL;
+		j += 2;
+	}
+	io_names[vq_num] = "serial-input";
+	io_names[vq_num + 1] = "serial-output";
+	err = portdev->vdev->config->find_vqs(portdev->vdev, nr_queues, vqs,
+				io_callbacks,
+				(const char **)io_names);
+	if (err)
+		goto free;
+	portdev->in_vqs[id] = vqs[vq_num];
+	portdev->out_vqs[id] = vqs[vq_num + 1];

I don't think this approach will work fine for port hot-plug /
hot-unplug cases at all.  For example, I first start qemu with one
port, at id 1.  Then I add a port at id 5, then at 2, then at 10.
Will that be fine?

yes.
In this case, the virtio-serial will create id 1's queue when probe the
device. Then, add port id 5, it will create the id 5's queue and the queues
of id 2-4 still be null.
we find the right ioport by vq_num, and only the io_name[vq_num] and
io_name[vq_num+1] are not null. So after portdev->vdev->config->find_vqs(),
the id 5's queues are created(see the changes in virtio-pci), the others 
are
still null.

quoted

+
+free:
+	kfree(io_names);
+	kfree(io_callbacks);
+	kfree(vqs);
+
+	return err;
+}
+
  static int add_port(struct ports_device *portdev, u32 id)
  {
  	char debugfs_name[16];

@@ -1163,6 +1212,14 @@ static int add_port(struct ports_device *portdev, u32 id)

  	port->outvq_full = false;

+	if (!portdev->in_vqs[port->id]&&  !portdev->out_vqs[port->id]) {
+		spin_lock(&portdev->ports_lock);
+		err = setup_port_vq(portdev, port->id);
+		spin_unlock(&portdev->ports_lock);
+		if (err)
+			goto free_port;
+	}
+
  	port->in_vq = portdev->in_vqs[port->id];
  	port->out_vq = portdev->out_vqs[port->id];

@@ -1614,8 +1671,8 @@ static int init_vqs(struct ports_device *portdev)
  			j += 2;
  			io_callbacks[j] = in_intr;
  			io_callbacks[j + 1] = out_intr;
-			io_names[j] = "input";
-			io_names[j + 1] = "output";
+			io_names[j] = NULL;
+			io_names[j + 1] = NULL;
  		}
  	}
  	/* Find the queues. */

@@ -1635,8 +1692,8 @@ static int init_vqs(struct ports_device *portdev)

  		for (i = 1; i<  nr_ports; i++) {
  			j += 2;
-			portdev->in_vqs[i] = vqs[j];
-			portdev->out_vqs[i] = vqs[j + 1];
+			portdev->in_vqs[i] = NULL;
+			portdev->out_vqs[i] = NULL;
  		}
  	}
  	kfree(io_names);

So a queue once created will not be removed unless the module is
removed or the device is removed.  That seems reasonable, port
hot-unplug will keep queues around, as is the case now.

As we use the virtio-serial with only a few io-ports, the maxport queues 
may
waste more memory. So we try to create queues when port hot-plug, as for
port hot-unplug there's no change.

		Amit

.

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