Re: [PATCH] dax: fix build warnings with FS_DAX and !FS_IOMAP

[Jan Kara <jack@suse.cz>]

On Tue 10-01-17 15:29:43, Ross Zwisler wrote:
> As reported by Arnd:
> 
> https://lkml.org/lkml/2017/1/10/756
> 
> Compiling with the following configuration:
> 
>   # CONFIG_EXT2_FS is not set
>   # CONFIG_EXT4_FS is not set
>   # CONFIG_XFS_FS is not set
>   # CONFIG_FS_IOMAP depends on the above filesystems, as is not set
>   CONFIG_FS_DAX=y
> 
> generates build warnings about unused functions in fs/dax.c:
> 
> fs/dax.c:878:12: warning: ‘dax_insert_mapping’ defined but not used [-Wunused-function]
>  static int dax_insert_mapping(struct address_space *mapping,
>             ^~~~~~~~~~~~~~~~~~
> fs/dax.c:572:12: warning: ‘copy_user_dax’ defined but not used [-Wunused-function]
>  static int copy_user_dax(struct block_device *bdev, sector_t sector, size_t size,
>             ^~~~~~~~~~~~~
> fs/dax.c:542:12: warning: ‘dax_load_hole’ defined but not used [-Wunused-function]
>  static int dax_load_hole(struct address_space *mapping, void **entry,
>             ^~~~~~~~~~~~~
> fs/dax.c:312:14: warning: ‘grab_mapping_entry’ defined but not used [-Wunused-function]
>  static void *grab_mapping_entry(struct address_space *mapping, pgoff_t index,
>               ^~~~~~~~~~~~~~~~~~
> 
> Now that the struct buffer_head based DAX fault paths and I/O path have
> been removed we really depend on iomap support being present for DAX.  Make
> this explicit by selecting FS_IOMAP if we compile in DAX support.
> 
> This allows us to remove conditional selections of FS_IOMAP when FS_DAX was
> present for ext2 and ext4, and to remove an #ifdef in fs/dax.c.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> Reported-by: Arnd Bergmann <arnd@arndb.de>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Christoph Hellwig <hch@lst.de>

Looks good. I agree that DAX without FS_IOMAP does not make sense. You can
add:

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

								Honza
> ---
>  fs/Kconfig      | 1 +
>  fs/dax.c        | 2 --
>  fs/ext2/Kconfig | 1 -
>  fs/ext4/Kconfig | 1 -
>  4 files changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/fs/Kconfig b/fs/Kconfig
> index c2a377c..83eab52 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -38,6 +38,7 @@ config FS_DAX
>  	bool "Direct Access (DAX) support"
>  	depends on MMU
>  	depends on !(ARM || MIPS || SPARC)
> +	select FS_IOMAP
>  	help
>  	  Direct Access (DAX) can be used on memory-backed block devices.
>  	  If the block device supports DAX and the filesystem supports DAX,
> diff --git a/fs/dax.c b/fs/dax.c
> index 5c74f60..083b950 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -969,7 +969,6 @@ int __dax_zero_page_range(struct block_device *bdev, sector_t sector,
>  }
>  EXPORT_SYMBOL_GPL(__dax_zero_page_range);
>  
> -#ifdef CONFIG_FS_IOMAP
>  static sector_t dax_iomap_sector(struct iomap *iomap, loff_t pos)
>  {
>  	return iomap->blkno + (((pos & PAGE_MASK) - iomap->offset) >> 9);
> @@ -1407,4 +1406,3 @@ int dax_iomap_pmd_fault(struct vm_area_struct *vma, unsigned long address,
>  }
>  EXPORT_SYMBOL_GPL(dax_iomap_pmd_fault);
>  #endif /* CONFIG_FS_DAX_PMD */
> -#endif /* CONFIG_FS_IOMAP */
> diff --git a/fs/ext2/Kconfig b/fs/ext2/Kconfig
> index 36bea5a..c634874e 100644
> --- a/fs/ext2/Kconfig
> +++ b/fs/ext2/Kconfig
> @@ -1,6 +1,5 @@
>  config EXT2_FS
>  	tristate "Second extended fs support"
> -	select FS_IOMAP if FS_DAX
>  	help
>  	  Ext2 is a standard Linux file system for hard disks.
>  
> diff --git a/fs/ext4/Kconfig b/fs/ext4/Kconfig
> index 7b90691..e38039f 100644
> --- a/fs/ext4/Kconfig
> +++ b/fs/ext4/Kconfig
> @@ -37,7 +37,6 @@ config EXT4_FS
>  	select CRC16
>  	select CRYPTO
>  	select CRYPTO_CRC32C
> -	select FS_IOMAP if FS_DAX
>  	help
>  	  This is the next generation of the ext3 filesystem.
>  
> -- 
> 2.7.4
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR