[PATCH 1/1] [virt] virtio-blk: Use ida to allocate disk index

[Mark Wu <dwu@redhat.com>]

Current index allocation in virtio-blk is based on a monotonically
increasing variable "index". It could cause some confusion about disk
name in the case of hot-plugging disks. And it's impossible to find the
lowest available index by just maintaining a simple index. So it's
changed to use ida to allocate index via referring to the index
allocation in scsi disk.

Signed-off-by: Mark Wu <dwu@redhat.com>
---
 drivers/block/virtio_blk.c |   37 ++++++++++++++++++++++++++++++++-----
 1 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 079c088..ba734b3 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -8,10 +8,14 @@
 #include <linux/scatterlist.h>
 #include <linux/string_helpers.h>
 #include <scsi/scsi_cmnd.h>
+#include <linux/idr.h>
 
 #define PART_BITS 4
 
-static int major, index;
+static int major;
+static DEFINE_SPINLOCK(vd_index_lock);
+static DEFINE_IDA(vd_index_ida);
+
 struct workqueue_struct *virtblk_wq;
 
 struct virtio_blk
@@ -23,6 +27,7 @@ struct virtio_blk
 
 	/* The disk structure for the kernel. */
 	struct gendisk *disk;
+	u32 index;
 
 	/* Request tracking. */
 	struct list_head reqs;
@@ -343,12 +348,26 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
 	struct request_queue *q;
 	int err;
 	u64 cap;
-	u32 v, blk_size, sg_elems, opt_io_size;
+	u32 v, blk_size, sg_elems, opt_io_size, index;
 	u16 min_io_size;
 	u8 physical_block_exp, alignment_offset;
 
-	if (index_to_minor(index) >= 1 << MINORBITS)
-		return -ENOSPC;
+	do {
+		if (!ida_pre_get(&vd_index_ida, GFP_KERNEL))
+			return err;
+
+		spin_lock(&vd_index_lock);
+		err = ida_get_new(&vd_index_ida, &index);
+		spin_unlock(&vd_index_lock);
+	} while (err == -EAGAIN);
+
+	if (err)
+		return err;
+
+	if (index_to_minor(index) >= 1 << MINORBITS) {
+		err =  -ENOSPC;
+		goto out_free_index;
+	}
 
 	/* We need to know how many segments before we allocate. */
 	err = virtio_config_val(vdev, VIRTIO_BLK_F_SEG_MAX,
@@ -421,7 +440,7 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
 	vblk->disk->private_data = vblk;
 	vblk->disk->fops = &virtblk_fops;
 	vblk->disk->driverfs_dev = &vdev->dev;
-	index++;
+	vblk->index = index;
 
 	/* configure queue flush support */
 	if (virtio_has_feature(vdev, VIRTIO_BLK_F_FLUSH))
@@ -516,6 +535,10 @@ out_free_vq:
 	vdev->config->del_vqs(vdev);
 out_free_vblk:
 	kfree(vblk);
+out_free_index:
+	spin_lock(&vd_index_lock);
+	ida_remove(&vd_index_ida, index);
+	spin_unlock(&vd_index_lock);
 out:
 	return err;
 }
@@ -529,6 +552,10 @@ static void __devexit virtblk_remove(struct virtio_device *vdev)
 	/* Nothing should be pending. */
 	BUG_ON(!list_empty(&vblk->reqs));
 
+	spin_lock(&vd_index_lock);
+	ida_remove(&vd_index_ida, vblk->index);
+	spin_unlock(&vd_index_lock);
+
 	/* Stop all the virtqueues. */
 	vdev->config->reset(vdev);
 
-- 
1.7.1