Re: [RFC][PATCH 01/11] fs: common implementation of file type conversions

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Mon, Dec 19, 2016 at 10:10:58PM +0200, Amir Goldstein wrote:
> Many file systems use a copy&paste implementation
> of dirent to on-disk file type conversions.
> 
> Create a common implementation to be used by file systems
> with some useful conversion helpers to reduce open coded
> file type conversions in file system code.
> 
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> ---
>  include/linux/file_type.h | 107 ++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/fs.h        |  17 +-------
>  2 files changed, 108 insertions(+), 16 deletions(-)
>  create mode 100644 include/linux/file_type.h
> 
> diff --git a/include/linux/file_type.h b/include/linux/file_type.h
> new file mode 100644
> index 0000000..03ee1a1
> --- /dev/null
> +++ b/include/linux/file_type.h
> @@ -0,0 +1,107 @@
> +#ifndef _LINUX_FILE_TYPE_H
> +#define _LINUX_FILE_TYPE_H
> +
> +/*
> + * This is a common implementation of dirent to fs on-disk
> + * file type conversion.  Although the fs on-disk bits are
> + * specific to every file system, in practice, many file systems
> + * use the exact same on-disk format to describe the lower 3
> + * file type bits that represent the 7 POSIX file types.
> + * All those file systems can use this generic code for the
> + * conversions:
> + *  i_mode -> fs on-disk file type (ftype)
> + *  fs on-disk file type (ftype) -> dirent file type (dtype)
> + *  i_mode -> dirent file type (dtype)
> + */
> +
> +/*
> + * struct dirent file types
> + * exposed to user via getdents(2), readdir(3)
> + *
> + * These match bits 12..15 of stat.st_mode
> + * (ie "(i_mode >> 12) & 15").
> + */
> +#define S_DT_SHIFT	12
> +#define S_DT(mode)	(((mode) & S_IFMT) >> S_DT_SHIFT)
> +#define DT_MASK		(S_IFMT >> S_DT_SHIFT)
> +
> +#define DT_UNKNOWN	0
> +#define DT_FIFO		S_DT(S_IFIFO) /* 1 */
> +#define DT_CHR		S_DT(S_IFCHR) /* 2 */
> +#define DT_DIR		S_DT(S_IFDIR) /* 4 */
> +#define DT_BLK		S_DT(S_IFBLK) /* 6 */
> +#define DT_REG		S_DT(S_IFREG) /* 8 */
> +#define DT_LNK		S_DT(S_IFLNK) /* 10 */
> +#define DT_SOCK		S_DT(S_IFSOCK) /* 12 */
> +#define DT_WHT		14
> +
> +#define DT_MAX		(DT_MASK + 1) /* 16 */
> +
> +/*
> + * fs on-disk file types.
> + * Only the low 3 bits are used for the POSIX file types.
> + * Other bits are reserved for fs private use.
> + *
> + * Note that no fs currently stores the whiteout type on-disk,
> + * so whiteout dirents are exposed to user as DT_CHR.
> + */
> +#define FT_UNKNOWN	0
> +#define FT_REG_FILE	1
> +#define FT_DIR		2
> +#define FT_CHRDEV	3
> +#define FT_BLKDEV	4
> +#define FT_FIFO		5
> +#define FT_SOCK		6
> +#define FT_SYMLINK	7
> +
> +#define FT_MAX		8
> +
> +/*
> + * fs on-disk file type to dirent file type conversion
> + */
> +static unsigned char fs_dtype_by_ftype[] = {
> +	DT_UNKNOWN,

[FT_UNKNOWN] = DT_UNKNOWN, etc?

It's not strictly necessary but it makes the mapping more explicit.

--D

> +	DT_REG,
> +	DT_DIR,
> +	DT_CHR,
> +	DT_BLK,
> +	DT_FIFO,
> +	DT_SOCK,
> +	DT_LNK
> +};
> +
> +static inline unsigned char fs_dtype(int filetype)
> +{
> +	if (filetype >= FT_MAX)
> +		return DT_UNKNOWN;
> +
> +	return fs_dtype_by_ftype[filetype];
> +}
> +
> +/*
> + * dirent file type to fs on-disk file type conversion
> + * Values not initialized explicitly are FT_UNKNOWN (0).
> + */
> +static unsigned char fs_ftype_by_dtype[DT_MAX] = {
> +	[DT_REG]	= FT_REG_FILE,
> +	[DT_DIR]	= FT_DIR,
> +	[DT_LNK]	= FT_SYMLINK,
> +	[DT_CHR]	= FT_CHRDEV,
> +	[DT_BLK]	= FT_BLKDEV,
> +	[DT_FIFO]	= FT_FIFO,
> +	[DT_SOCK]	= FT_SOCK,
> +};
> +
> +/* st_mode to fs on-disk file type conversion */
> +static inline unsigned char fs_umode_to_ftype(umode_t mode)
> +{
> +	return fs_ftype_by_dtype[S_DT(mode)];
> +}
> +
> +/* st_mode to dirent file type conversion */
> +static inline unsigned char fs_umode_to_dtype(umode_t mode)
> +{
> +	return fs_dtype(fs_umode_to_ftype(mode));
> +}
> +
> +#endif
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index e6e4146..8f1580d 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -31,6 +31,7 @@
>  #include <linux/workqueue.h>
>  #include <linux/percpu-rwsem.h>
>  #include <linux/delayed_call.h>
> +#include <linux/file_type.h>
>  
>  #include <asm/byteorder.h>
>  #include <uapi/linux/fs.h>
> @@ -1582,22 +1583,6 @@ int fiemap_fill_next_extent(struct fiemap_extent_info *info, u64 logical,
>  int fiemap_check_flags(struct fiemap_extent_info *fieinfo, u32 fs_flags);
>  
>  /*
> - * File types
> - *
> - * NOTE! These match bits 12..15 of stat.st_mode
> - * (ie "(i_mode >> 12) & 15").
> - */
> -#define DT_UNKNOWN	0
> -#define DT_FIFO		1
> -#define DT_CHR		2
> -#define DT_DIR		4
> -#define DT_BLK		6
> -#define DT_REG		8
> -#define DT_LNK		10
> -#define DT_SOCK		12
> -#define DT_WHT		14
> -
> -/*
>   * This is the "filldir" function type, used by readdir() to let
>   * the kernel specify what kind of dirent layout it wants to have.
>   * This allows the kernel to read directories into kernel space or
> -- 
> 2.7.4
>