[RFC][PATCH v2 01/11] fs: common implementation of file type conversions

[Amir Goldstein <amir73il@gmail.com>]

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


Fixed a comment by Darrick and a build warning reported by kbuild robot.

These changes are local to the common implementation, so not re-spamming
with all the non changed fs patches.

v2:
- s/DT_MASK/S_DT_MASK to fix redefinition in drivers/scsi/qla2xxx/qla_def.h
- explicit initialization of fs_dtype_by_ftype[] using [FT_*] = DT_*

v1:
- initial implementation

diff --git a/include/linux/file_type.h b/include/linux/file_type.h
new file mode 100644
index 0000000..bb218f4
--- /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 S_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		(S_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[FT_MAX] = {
+	[FT_UNKNOWN]	= DT_UNKNOWN,
+	[FT_REG_FILE]	= DT_REG,
+	[FT_DIR]	= DT_DIR,
+	[FT_CHRDEV]	= DT_CHR,
+	[FT_BLKDEV]	= DT_BLK,
+	[FT_FIFO]	= DT_FIFO,
+	[FT_SOCK]	= DT_SOCK,
+	[FT_SYMLINK]	= 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