virtio-blk: use ida to allocate disk index

Based on a patch by Mark Wu <dwu@redhat.com>

Current index allocation in virtio-blk is based on a monotonically
increasing variable "index". This means we'll run out of numbers
after a while.  It also could cause confusion about the disk
name in the case of hot-plugging disks.
Change virtio-blk to use ida to allocate index, instead.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 24 insertions, 6 deletions

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 079c08808d8a..e7a5750a93d9 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -8,10 +8,13 @@
 #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_IDA(vd_index_ida);
+
 struct workqueue_struct *virtblk_wq;
 
 struct virtio_blk
@@ -35,6 +38,9 @@ struct virtio_blk
         /* What host tells us, plus 2 for header & tailer. */
         unsigned int sg_elems;
 
+        /* Ida index - used to track minor number allocations. */
+        int index;
+
         /* Scatterlist: can be too big for stack. */
         struct scatterlist sg[/*sg_elems*/];
 };
@@ -276,6 +282,11 @@ static int index_to_minor(int index)
         return index << PART_BITS;
 }
 
+static int minor_to_index(int minor)
+{
+        return minor >> PART_BITS;
+}
+
 static ssize_t virtblk_serial_show(struct device *dev,
                                 struct device_attribute *attr, char *buf)
 {
@@ -341,14 +352,17 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
 {
         struct virtio_blk *vblk;
         struct request_queue *q;
-        int err;
+        int err, index;
         u64 cap;
         u32 v, blk_size, sg_elems, opt_io_size;
         u16 min_io_size;
         u8 physical_block_exp, alignment_offset;
 
-        if (index_to_minor(index) >= 1 << MINORBITS)
-                return -ENOSPC;
+        err = ida_simple_get(&vd_index_ida, 0, minor_to_index(1 << MINORBITS),
+                             GFP_KERNEL);
+        if (err < 0)
+                goto out;
+        index = err;
 
         /* We need to know how many segments before we allocate. */
         err = virtio_config_val(vdev, VIRTIO_BLK_F_SEG_MAX,
@@ -365,7 +379,7 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
                                     sizeof(vblk->sg[0]) * sg_elems, GFP_KERNEL);
         if (!vblk) {
                 err = -ENOMEM;
-                goto out;
+                goto out_free_index;
         }
 
         INIT_LIST_HEAD(&vblk->reqs);
@@ -421,7 +435,7 @@ 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 +530,8 @@ out_free_vq:
         vdev->config->del_vqs(vdev);
 out_free_vblk:
         kfree(vblk);
+out_free_index:
+        ida_simple_remove(&vd_index_ida, index);
 out:
         return err;
 }
@@ -523,6 +539,7 @@ out:
 static void __devexit virtblk_remove(struct virtio_device *vdev)
 {
         struct virtio_blk *vblk = vdev->priv;
+        int index = vblk->index;
 
         flush_work(&vblk->config_work);
 
@@ -538,6 +555,7 @@ static void __devexit virtblk_remove(struct virtio_device *vdev)
         mempool_destroy(vblk->pool);
         vdev->config->del_vqs(vdev);
         kfree(vblk);
+        ida_simple_remove(&vd_index_ida, index);
 }
 
 static const struct virtio_device_id id_table[] = {