net/9p: Add multi channel support.

This is needed for supporting multiple mount points.

We can find out the device names to be used with mount by checking

/sys/devices/virtio-pci/virtio*/device file

if the device file have value 9 then the specific virtio device can
be used for mounting.

ex:
 #cat /sys/devices/virtio-pci/virtio1/device
 9

now we can mount using
# mount -t 9p -o trans=virtio virtio1  /mnt/
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

include/linux/virtio_9p.h

@@ -6,6 +6,6 @@
 #include <linux/virtio_config.h>
 
 /* Maximum number of virtio channels per partition (1 for now) */
-#define MAX_9P_CHAN	1
+#define MAX_9P_CHAN	10
 
 #endif /* _LINUX_VIRTIO_9P_H */

net/9p/trans_virtio.c

@@ -296,13 +296,15 @@ p9_virtio_create(struct p9_client *client, const char *devname, char *args)
 
 	mutex_lock(&virtio_9p_lock);
 	while (index < MAX_9P_CHAN) {
-		if (chan->initialized && !chan->inuse) {
-			chan->inuse = true;
-			break;
-		} else {
-			index++;
-			chan = &channels[index];
+		if (chan->initialized &&
+			!strcmp(devname, dev_name(&chan->vdev->dev))) {
+			if (!chan->inuse) {
+				chan->inuse = true;
+				break;
+			}
 		}
+		index++;
+		chan = &channels[index];
 	}
 	mutex_unlock(&virtio_9p_lock);