[v3,1/4] dax: introduce a fs_dax_get_by_bdev() helper

Add a helper that can replace the following common pattern:

	if (blk_queue_dax(bdev->bd_queue))
		fs_dax_get_by_host(bdev->bd_disk->disk_name);

This will be used to move dax_device lookup from iomap-operation time to
fs-mount time.

Cc: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 drivers/dax/super.c |   10 ++++++++++
 include/linux/dax.h |    6 ++++++
 2 files changed, 16 insertions(+)

On Wed, Aug 30, 2017 at 12:43:52PM -0700, Dan Williams wrote:
> Add a helper that can replace the following common pattern:
> 
> 	if (blk_queue_dax(bdev->bd_queue))
> 		fs_dax_get_by_host(bdev->bd_disk->disk_name);
> 
> This will be used to move dax_device lookup from iomap-operation time to
> fs-mount time.
> 
> Cc: Jan Kara <jack@suse.cz>
> Cc: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

> ---
>  drivers/dax/super.c |   10 ++++++++++
>  include/linux/dax.h |    6 ++++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index 938eb4868f7f..b699aac268a6 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -46,6 +46,8 @@ void dax_read_unlock(int id)
>  EXPORT_SYMBOL_GPL(dax_read_unlock);
>  
>  #ifdef CONFIG_BLOCK
> +#include <linux/blkdev.h>
> +
>  int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
>  		pgoff_t *pgoff)
>  {
> @@ -59,6 +61,14 @@ int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
>  }
>  EXPORT_SYMBOL(bdev_dax_pgoff);
>  
> +struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
> +{
> +	if (!blk_queue_dax(bdev->bd_queue))
> +		return NULL;
> +	return fs_dax_get_by_host(bdev->bd_disk->disk_name);
> +}
> +EXPORT_SYMBOL_GPL(fs_dax_get_by_bdev);
> +
>  /**
>   * __bdev_dax_supported() - Check if the device supports dax for filesystem
>   * @sb: The superblock of the device
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index df97b7af7e2c..ac8afa18f707 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -57,6 +57,7 @@ static inline void fs_put_dax(struct dax_device *dax_dev)
>  	put_dax(dax_dev);
>  }
>  
> +struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev);
>  #else
>  static inline int bdev_dax_supported(struct super_block *sb, int blocksize)
>  {
> @@ -71,6 +72,11 @@ static inline struct dax_device *fs_dax_get_by_host(const char *host)
>  static inline void fs_put_dax(struct dax_device *dax_dev)
>  {
>  }
> +
> +static inline struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
> +{
> +	return NULL;
> +}
>  #endif
>  
>  int dax_read_lock(void);
> 
> --
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On Wed 30-08-17 12:43:52, Dan Williams wrote:
> Add a helper that can replace the following common pattern:
> 
> 	if (blk_queue_dax(bdev->bd_queue))
> 		fs_dax_get_by_host(bdev->bd_disk->disk_name);
> 
> This will be used to move dax_device lookup from iomap-operation time to
> fs-mount time.
> 
> Cc: Jan Kara <jack@suse.cz>
> Cc: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

Looks fine,

Reviewed-by: Christoph Hellwig <hch@lst.de>