fs: common implementation of file type

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>
Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Signed-off-by: Jan Kara <jack@suse.cz>

2 files changed, 107 insertions, 1 deletions

diff --git a/fs/Makefile b/fs/Makefile
index 293733f61594..23fcd8c164a3 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -12,7 +12,8 @@ obj-y :=	open.o read_write.o file_table.o super.o \
 		attr.o bad_inode.o file.o filesystems.o namespace.o \
 		seq_file.o xattr.o libfs.o fs-writeback.o \
 		pnode.o splice.o sync.o utimes.o d_path.o \
-		stack.o fs_struct.o statfs.o fs_pin.o nsfs.o
+		stack.o fs_struct.o statfs.o fs_pin.o nsfs.o \
+		fs_types.o
 
 ifeq ($(CONFIG_BLOCK),y)
 obj-y +=	buffer.o block_dev.o direct-io.o mpage.o
diff --git a/fs/fs_types.c b/fs/fs_types.c
new file mode 100644
index 000000000000..78365e5dc08c
--- /dev/null
+++ b/fs/fs_types.c
@@ -0,0 +1,105 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/fs.h>
+#include <linux/export.h>
+
+/*
+ * fs on-disk file type to dirent file type conversion
+ */
+static const 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
+};
+
+/**
+ * fs_ftype_to_dtype() - fs on-disk file type to dirent type.
+ * @filetype: The on-disk file type to convert.
+ *
+ * This function converts the on-disk file type value (FT_*) to the directory
+ * entry type (DT_*).
+ *
+ * Context: Any context.
+ * Return:
+ * * DT_UNKNOWN		- Unknown type
+ * * DT_FIFO		- FIFO
+ * * DT_CHR		- Character device
+ * * DT_DIR		- Directory
+ * * DT_BLK		- Block device
+ * * DT_REG		- Regular file
+ * * DT_LNK		- Symbolic link
+ * * DT_SOCK		- Local-domain socket
+ */
+unsigned char fs_ftype_to_dtype(unsigned int filetype)
+{
+	if (filetype >= FT_MAX)
+		return DT_UNKNOWN;
+
+	return fs_dtype_by_ftype[filetype];
+}
+EXPORT_SYMBOL_GPL(fs_ftype_to_dtype);
+
+/*
+ * dirent file type to fs on-disk file type conversion
+ * Values not initialized explicitly are FT_UNKNOWN (0).
+ */
+static const 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,
+};
+
+/**
+ * fs_umode_to_ftype() - file mode to on-disk file type.
+ * @mode: The file mode to convert.
+ *
+ * This function converts the file mode value to the on-disk file type (FT_*).
+ *
+ * Context: Any context.
+ * Return:
+ * * FT_UNKNOWN		- Unknown type
+ * * FT_REG_FILE	- Regular file
+ * * FT_DIR		- Directory
+ * * FT_CHRDEV		- Character device
+ * * FT_BLKDEV		- Block device
+ * * FT_FIFO		- FIFO
+ * * FT_SOCK		- Local-domain socket
+ * * FT_SYMLINK		- Symbolic link
+ */
+unsigned char fs_umode_to_ftype(umode_t mode)
+{
+	return fs_ftype_by_dtype[S_DT(mode)];
+}
+EXPORT_SYMBOL_GPL(fs_umode_to_ftype);
+
+/**
+ * fs_umode_to_dtype() - file mode to dirent file type.
+ * @mode: The file mode to convert.
+ *
+ * This function converts the file mode value to the directory
+ * entry type (DT_*).
+ *
+ * Context: Any context.
+ * Return:
+ * * DT_UNKNOWN		- Unknown type
+ * * DT_FIFO		- FIFO
+ * * DT_CHR		- Character device
+ * * DT_DIR		- Directory
+ * * DT_BLK		- Block device
+ * * DT_REG		- Regular file
+ * * DT_LNK		- Symbolic link
+ * * DT_SOCK		- Local-domain socket
+ */
+unsigned char fs_umode_to_dtype(umode_t mode)
+{
+	return fs_ftype_to_dtype(fs_umode_to_ftype(mode));
+}
+EXPORT_SYMBOL_GPL(fs_umode_to_dtype);