net/9p: Add sysfs mount_tag file for virtio 9P device

This adds a new file for virtio 9P device. The file
contain details of the mount device name that should
be used to mount the 9P file system.

Ex: /sys/devices/virtio-pci/virtio1/mount_tag  file now
contian the tag name to be used to mount the 9P file system.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

2 files changed, 21 insertions, 0 deletions

diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index f508c651e53d..40d1709bdbf4 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -98,6 +98,7 @@ struct virtio_device {
         void *priv;
 };
 
+#define dev_to_virtio(dev) container_of(dev, struct virtio_device, dev)
 int register_virtio_device(struct virtio_device *dev);
 void unregister_virtio_device(struct virtio_device *dev);
 
diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 026775ad391a..afde1a89fbb3 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -220,6 +220,20 @@ p9_virtio_request(struct p9_client *client, struct p9_req_t *req)
         return 0;
 }
 
+static ssize_t p9_mount_tag_show(struct device *dev,
+                                struct device_attribute *attr, char *buf)
+{
+        struct virtio_chan *chan;
+        struct virtio_device *vdev;
+
+        vdev = dev_to_virtio(dev);
+        chan = vdev->priv;
+
+        return snprintf(buf, chan->tag_len + 1, "%s", chan->tag);
+}
+
+static DEVICE_ATTR(mount_tag, 0444, p9_mount_tag_show, NULL);
+
 /**
  * p9_virtio_probe - probe for existence of 9P virtio channels
  * @vdev: virtio device to probe
@@ -273,6 +287,11 @@ static int p9_virtio_probe(struct virtio_device *vdev)
                         tag, tag_len);
         chan->tag = tag;
         chan->tag_len = tag_len;
+        err = sysfs_create_file(&(vdev->dev.kobj), &dev_attr_mount_tag.attr);
+        if (err) {
+                kfree(tag);
+                goto out_free_vq;
+        }
         mutex_lock(&virtio_9p_lock);
         list_add_tail(&chan->chan_list, &virtio_chan_list);
         mutex_unlock(&virtio_9p_lock);
@@ -348,6 +367,7 @@ static void p9_virtio_remove(struct virtio_device *vdev)
         mutex_lock(&virtio_9p_lock);
         list_del(&chan->chan_list);
         mutex_unlock(&virtio_9p_lock);
+        sysfs_remove_file(&(vdev->dev.kobj), &dev_attr_mount_tag.attr);
         kfree(chan->tag);
         kfree(chan);