Re: [PATCH 14/29] fsdax: simplify the pgoff calculation

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Nov 09, 2021 at 09:32:54AM +0100, Christoph Hellwig wrote:
> Replace the two steps of dax_iomap_sector and bdev_dax_pgoff with a
> single dax_iomap_pgoff helper that avoids lots of cumbersome sector
> conversions.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  drivers/dax/super.c | 14 --------------
>  fs/dax.c            | 35 ++++++++++-------------------------
>  include/linux/dax.h |  1 -
>  3 files changed, 10 insertions(+), 40 deletions(-)
> 
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index 803942586d1b6..c0910687fbcb2 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -67,20 +67,6 @@ void dax_remove_host(struct gendisk *disk)
>  }
>  EXPORT_SYMBOL_GPL(dax_remove_host);
>  
> -int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
> -		pgoff_t *pgoff)
> -{
> -	sector_t start_sect = bdev ? get_start_sect(bdev) : 0;
> -	phys_addr_t phys_off = (start_sect + sector) * 512;
> -
> -	if (pgoff)
> -		*pgoff = PHYS_PFN(phys_off);
> -	if (phys_off % PAGE_SIZE || size % PAGE_SIZE)

AFAICT, we're relying on fs_dax_get_by_bdev to have validated this
previously, which is why the error return stuff goes away?

If so,
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D


> -		return -EINVAL;
> -	return 0;
> -}
> -EXPORT_SYMBOL(bdev_dax_pgoff);
> -
>  /**
>   * dax_get_by_host() - temporary lookup mechanism for filesystem-dax
>   * @bdev: block device to find a dax_device for
> diff --git a/fs/dax.c b/fs/dax.c
> index e51b4129d1b65..5364549d67a48 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -709,23 +709,22 @@ int dax_invalidate_mapping_entry_sync(struct address_space *mapping,
>  	return __dax_invalidate_entry(mapping, index, false);
>  }
>  
> -static sector_t dax_iomap_sector(const struct iomap *iomap, loff_t pos)
> +static pgoff_t dax_iomap_pgoff(const struct iomap *iomap, loff_t pos)
>  {
> -	return (iomap->addr + (pos & PAGE_MASK) - iomap->offset) >> 9;
> +	phys_addr_t paddr = iomap->addr + (pos & PAGE_MASK) - iomap->offset;
> +
> +	if (iomap->bdev)
> +		paddr += (get_start_sect(iomap->bdev) << SECTOR_SHIFT);
> +	return PHYS_PFN(paddr);
>  }
>  
>  static int copy_cow_page_dax(struct vm_fault *vmf, const struct iomap_iter *iter)
>  {
> -	sector_t sector = dax_iomap_sector(&iter->iomap, iter->pos);
> +	pgoff_t pgoff = dax_iomap_pgoff(&iter->iomap, iter->pos);
>  	void *vto, *kaddr;
> -	pgoff_t pgoff;
>  	long rc;
>  	int id;
>  
> -	rc = bdev_dax_pgoff(iter->iomap.bdev, sector, PAGE_SIZE, &pgoff);
> -	if (rc)
> -		return rc;
> -
>  	id = dax_read_lock();
>  	rc = dax_direct_access(iter->iomap.dax_dev, pgoff, 1, &kaddr, NULL);
>  	if (rc < 0) {
> @@ -1013,14 +1012,10 @@ EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);
>  static int dax_iomap_pfn(const struct iomap *iomap, loff_t pos, size_t size,
>  			 pfn_t *pfnp)
>  {
> -	const sector_t sector = dax_iomap_sector(iomap, pos);
> -	pgoff_t pgoff;
> +	pgoff_t pgoff = dax_iomap_pgoff(iomap, pos);
>  	int id, rc;
>  	long length;
>  
> -	rc = bdev_dax_pgoff(iomap->bdev, sector, size, &pgoff);
> -	if (rc)
> -		return rc;
>  	id = dax_read_lock();
>  	length = dax_direct_access(iomap->dax_dev, pgoff, PHYS_PFN(size),
>  				   NULL, pfnp);
> @@ -1129,7 +1124,7 @@ static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
>  s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
>  {
>  	sector_t sector = iomap_sector(iomap, pos & PAGE_MASK);
> -	pgoff_t pgoff;
> +	pgoff_t pgoff = dax_iomap_pgoff(iomap, pos);
>  	long rc, id;
>  	void *kaddr;
>  	bool page_aligned = false;
> @@ -1140,10 +1135,6 @@ s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
>  	    (size == PAGE_SIZE))
>  		page_aligned = true;
>  
> -	rc = bdev_dax_pgoff(iomap->bdev, sector, PAGE_SIZE, &pgoff);
> -	if (rc)
> -		return rc;
> -
>  	id = dax_read_lock();
>  
>  	if (page_aligned)
> @@ -1169,7 +1160,6 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
>  	const struct iomap *iomap = &iomi->iomap;
>  	loff_t length = iomap_length(iomi);
>  	loff_t pos = iomi->pos;
> -	struct block_device *bdev = iomap->bdev;
>  	struct dax_device *dax_dev = iomap->dax_dev;
>  	loff_t end = pos + length, done = 0;
>  	ssize_t ret = 0;
> @@ -1203,9 +1193,8 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
>  	while (pos < end) {
>  		unsigned offset = pos & (PAGE_SIZE - 1);
>  		const size_t size = ALIGN(length + offset, PAGE_SIZE);
> -		const sector_t sector = dax_iomap_sector(iomap, pos);
> +		pgoff_t pgoff = dax_iomap_pgoff(iomap, pos);
>  		ssize_t map_len;
> -		pgoff_t pgoff;
>  		void *kaddr;
>  
>  		if (fatal_signal_pending(current)) {
> @@ -1213,10 +1202,6 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
>  			break;
>  		}
>  
> -		ret = bdev_dax_pgoff(bdev, sector, size, &pgoff);
> -		if (ret)
> -			break;
> -
>  		map_len = dax_direct_access(dax_dev, pgoff, PHYS_PFN(size),
>  				&kaddr, NULL);
>  		if (map_len < 0) {
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index 439c3c70e347b..324363b798ecd 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -107,7 +107,6 @@ static inline bool daxdev_mapping_supported(struct vm_area_struct *vma,
>  #endif
>  
>  struct writeback_control;
> -int bdev_dax_pgoff(struct block_device *, sector_t, size_t, pgoff_t *pgoff);
>  #if IS_ENABLED(CONFIG_FS_DAX)
>  int dax_add_host(struct dax_device *dax_dev, struct gendisk *disk);
>  void dax_remove_host(struct gendisk *disk);
> -- 
> 2.30.2
>