[PATCH v4 1/7] iov_iter: Change the direction macros into an enum

[David Howells <dhowells@xxxxxxxxxx>]

Change the ITER_SOURCE and ITER_DEST direction macros into an enum and
provide three new helper functions:

 iov_iter_dir() - returns the iterator direction
 iov_iter_is_dest() - returns true if it's an ITER_DEST iterator
 iov_iter_is_source() - returns true if it's an ITER_SOURCE iterator

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---

 include/linux/uio.h |   32 +++++++++++++++++++++++++++-----
 1 file changed, 27 insertions(+), 5 deletions(-)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index 9f158238edba..4b0f4a773d90 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -29,8 +29,10 @@ enum iter_type {
 	ITER_UBUF,
 };
 
-#define ITER_SOURCE	1	// == WRITE
-#define ITER_DEST	0	// == READ
+enum iter_dir {
+	ITER_DEST	= 0,	// == READ
+	ITER_SOURCE	= 1,	// == WRITE
+} __mode(byte);
 
 struct iov_iter_state {
 	size_t iov_offset;
@@ -39,9 +41,9 @@ struct iov_iter_state {
 };
 
 struct iov_iter {
-	u8 iter_type;
+	enum iter_type iter_type __mode(byte);
 	bool nofault;
-	bool data_source;
+	enum iter_dir data_source;
 	bool user_backed;
 	union {
 		size_t iov_offset;
@@ -114,9 +116,29 @@ static inline bool iov_iter_is_xarray(const struct iov_iter *i)
 	return iov_iter_type(i) == ITER_XARRAY;
 }
 
+static inline enum iter_dir iov_iter_dir(const struct iov_iter *i)
+{
+	return i->data_source;
+}
+
+static inline bool iov_iter_is_source(const struct iov_iter *i)
+{
+	return iov_iter_dir(i) == ITER_SOURCE; /* ie. WRITE */
+}
+
+static inline bool iov_iter_is_dest(const struct iov_iter *i)
+{
+	return iov_iter_dir(i) == ITER_DEST; /* ie. READ */
+}
+
+static inline bool iov_iter_dir_valid(enum iter_dir direction)
+{
+	return direction == ITER_DEST || direction == ITER_SOURCE;
+}
+
 static inline unsigned char iov_iter_rw(const struct iov_iter *i)
 {
-	return i->data_source ? WRITE : READ;
+	return iov_iter_dir(i) == ITER_SOURCE ? WRITE : READ;
 }
 
 static inline bool user_backed_iter(const struct iov_iter *i)