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SubjectRe: [PATCH 1/1] [virt] virtio-blk: Use ida to allocate disk index
On Wed, Jun 01, 2011 at 03:24:29AM -0400, Mark Wu wrote:
> 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);

As we get index first thing in _probe, let's remove last thing
in _remove.

I'm not sure violating the rule of cleanup
in the reverse order of initialization can lead
to problems here, but it's better to stick to this rule regardless,
IMO.

> --
> 1.7.1


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