1 files changed, 51 insertions, 13 deletions

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 258bc2ae2885..23b7c48df843 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -225,16 +225,6 @@ static int virtblk_ioctl(struct block_device *bdev, fmode_t mode,
         struct gendisk *disk = bdev->bd_disk;
         struct virtio_blk *vblk = disk->private_data;
 
-        if (cmd == 0x56424944) { /* 'VBID' */
-                void __user *usr_data = (void __user *)data;
-                char id_str[VIRTIO_BLK_ID_BYTES];
-                int err;
-
-                err = virtblk_get_id(disk, id_str);
-                if (!err && copy_to_user(usr_data, id_str, VIRTIO_BLK_ID_BYTES))
-                        err = -EFAULT;
-                return err;
-        }
         /*
          * Only allow the generic SCSI ioctls if the host can support it.
          */
@@ -281,6 +271,27 @@ static int index_to_minor(int index)
         return index << PART_BITS;
 }
 
+static ssize_t virtblk_serial_show(struct device *dev,
+                                struct device_attribute *attr, char *buf)
+{
+        struct gendisk *disk = dev_to_disk(dev);
+        int err;
+
+        /* sysfs gives us a PAGE_SIZE buffer */
+        BUILD_BUG_ON(PAGE_SIZE < VIRTIO_BLK_ID_BYTES);
+
+        buf[VIRTIO_BLK_ID_BYTES] = '\0';
+        err = virtblk_get_id(disk, buf);
+        if (!err)
+                return strlen(buf);
+
+        if (err == -EIO) /* Unsupported? Make it empty. */
+                return 0;
+
+        return err;
+}
+DEVICE_ATTR(serial, S_IRUGO, virtblk_serial_show, NULL);
+
 static int __devinit virtblk_probe(struct virtio_device *vdev)
 {
         struct virtio_blk *vblk;
@@ -366,12 +377,32 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
         vblk->disk->driverfs_dev = &vdev->dev;
         index++;
 
-        /* If barriers are supported, tell block layer that queue is ordered */
-        if (virtio_has_feature(vdev, VIRTIO_BLK_F_FLUSH))
+        if (virtio_has_feature(vdev, VIRTIO_BLK_F_FLUSH)) {
+                /*
+                 * If the FLUSH feature is supported we do have support for
+                 * flushing a volatile write cache on the host.  Use that
+                 * to implement write barrier support.
+                 */
                 blk_queue_ordered(q, QUEUE_ORDERED_DRAIN_FLUSH,
                                   virtblk_prepare_flush);
-        else if (virtio_has_feature(vdev, VIRTIO_BLK_F_BARRIER))
+        } else if (virtio_has_feature(vdev, VIRTIO_BLK_F_BARRIER)) {
+                /*
+                 * If the BARRIER feature is supported the host expects us
+                 * to order request by tags.  This implies there is not
+                 * volatile write cache on the host, and that the host
+                 * never re-orders outstanding I/O.  This feature is not
+                 * useful for real life scenarious and deprecated.
+                 */
                 blk_queue_ordered(q, QUEUE_ORDERED_TAG, NULL);
+        } else {
+                /*
+                 * If the FLUSH feature is not supported we must assume that
+                 * the host does not perform any kind of volatile write
+                 * caching. We still need to drain the queue to provider
+                 * proper barrier semantics.
+                 */
+                blk_queue_ordered(q, QUEUE_ORDERED_DRAIN, NULL);
+        }
 
         /* If disk is read-only in the host, the guest should obey */
         if (virtio_has_feature(vdev, VIRTIO_BLK_F_RO))
@@ -445,8 +476,15 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
 
 
         add_disk(vblk->disk);
+        err = device_create_file(disk_to_dev(vblk->disk), &dev_attr_serial);
+        if (err)
+                goto out_del_disk;
+
         return 0;
 
+out_del_disk:
+        del_gendisk(vblk->disk);
+        blk_cleanup_queue(vblk->disk->queue);
 out_put_disk:
         put_disk(vblk->disk);
 out_mempool: