Linux Virtualization - Jun 2011 - [PATCH 1/1] [virt] virtio-blk: Use ida to allocate disk index

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 at 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

On 06/01/2011 03:24 AM, Mark Wu wrote:
> -	if (index_to_minor(index)>= 1<<  MINORBITS)
> -		return -ENOSPC;
> +	do {
> +		if (!ida_pre_get(&vd_index_ida, GFP_KERNEL))
> +			return err;
> +
There's a problem in above code: err is not initialized before using, so 
change it to return -1;
+       do {
+               if (!ida_pre_get(&vd_index_ida, GFP_KERNEL))
+                       return -1;

On Wed,  1 Jun 2011 03:24:29 -0400, Mark Wu <dwu at redhat.com>
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 at redhat.com>
Hi Mark,

   I don't believe that we do disk probes in parallel, so the spinlock
is unnecessary.  Otherwise, this looks good.

Thanks,
Rusty.

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 at 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

On Wed, Jun 01, 2011 at 04:25:48AM -0400, Mark Wu wrote:
> On 06/01/2011 03:24 AM, Mark Wu wrote:
> >-	if (index_to_minor(index)>= 1<<  MINORBITS)
> >-		return -ENOSPC;
> >+	do {
> >+		if (!ida_pre_get(&vd_index_ida, GFP_KERNEL))
> >+			return err;
> >+
> There's a problem in above code: err is not initialized before
> using, so change it to return -1;
> +       do {
> +               if (!ida_pre_get(&vd_index_ida, GFP_KERNEL))
> +                       return -1;
Not -1. Pls return -ENOMEM.

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 at 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..f13b758 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 -ENOMEM;
+
+		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;
 }
@@ -538,6 +561,10 @@ static void __devexit virtblk_remove(struct virtio_device
*vdev)
 	mempool_destroy(vblk->pool);
 	vdev->config->del_vqs(vdev);
 	kfree(vblk);
+
+	spin_lock(&vd_index_lock);
+	ida_remove(&vd_index_ida, vblk->index);
+	spin_unlock(&vd_index_lock);
 }
 
 static const struct virtio_device_id id_table[] = {
-- 
1.7.1

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 at redhat.com>
---
 drivers/block/virtio_blk.c |   28 +++++++++++++++++++++++-----
 1 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 079c088..bf81ab6 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
@@ -23,6 +26,7 @@ struct virtio_blk
 
 	/* The disk structure for the kernel. */
 	struct gendisk *disk;
+	u32 index;
 
 	/* Request tracking. */
 	struct list_head reqs;
@@ -343,12 +347,23 @@ 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 -ENOMEM;
+		err = ida_get_new(&vd_index_ida, &index);
+	} 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 +436,7 @@ 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 +531,8 @@ out_free_vq:
 	vdev->config->del_vqs(vdev);
 out_free_vblk:
 	kfree(vblk);
+out_free_index:
+	ida_remove(&vd_index_ida, index);
 out:
 	return err;
 }
@@ -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_remove(&vd_index_ida, vblk->index);
 }
 
 static const struct virtio_device_id id_table[] = {
-- 
1.7.1