Re: [PATCH 5/5] dax,iomap: Add helper dax_iomap_zero() to zero a range

[Christoph Hellwig <hch@infradead.org>]

> +int dax_iomap_zero(loff_t pos, unsigned offset, unsigned size,
> +			      struct iomap *iomap)
>  {
>  	pgoff_t pgoff;
>  	long rc, id;
> +	sector_t sector = iomap_sector(iomap, pos & PAGE_MASK);
>  
> -	rc = bdev_dax_pgoff(bdev, sector, PAGE_SIZE, &pgoff);
> +	rc = bdev_dax_pgoff(iomap->bdev, sector, PAGE_SIZE, &pgoff);
>  	if (rc)
>  		return rc;
>  
>  	id = dax_read_lock();
> -	rc = dax_zero_page_range(dax_dev, pgoff, offset, size);
> +	rc = dax_zero_page_range(iomap->dax_dev, pgoff, offset, size);
>  	dax_read_unlock(id);
>  	return rc;
>  }
> -EXPORT_SYMBOL_GPL(__dax_zero_page_range);
> +EXPORT_SYMBOL_GPL(dax_iomap_zero);

This function is only used by fs/iomap/buffered-io.c, so no need to
export it.

>  #ifdef CONFIG_FS_DAX
> -int __dax_zero_page_range(struct block_device *bdev,
> -		struct dax_device *dax_dev, sector_t sector,
> -		unsigned int offset, unsigned int length);
> +int dax_iomap_zero(loff_t pos, unsigned offset, unsigned size,
> +			      struct iomap *iomap);
>  #else
> -static inline int __dax_zero_page_range(struct block_device *bdev,
> -		struct dax_device *dax_dev, sector_t sector,
> -		unsigned int offset, unsigned int length)
> +static inline int dax_iomap_zero(loff_t pos, unsigned offset, unsigned size,
> +				 struct iomap *iomap)
>  {
>  	return -ENXIO;
>  }

Given that the only caller is under an IS_DAX() check you could just
declare the function unconditionally and let the compiler optimize
away the guaranteed dead call for the !CONFIG_FS_DAX case, like we
do with various other functions.