VFS: Add a whiteout dentry type

Add DCACHE_WHITEOUT_TYPE and provide a d_is_whiteout() accessor function.  A
d_is_miss() accessor is also added for ordinary cache misses and
d_is_negative() is modified to indicate either an ordinary miss or an enforced
miss (whiteout).
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/dcache.h

@@ -215,11 +215,12 @@ struct dentry_operations {
 #define DCACHE_LRU_LIST			0x00080000
 
 #define DCACHE_ENTRY_TYPE		0x00700000
-#define DCACHE_MISS_TYPE		0x00000000 /* Negative dentry */
-#define DCACHE_DIRECTORY_TYPE		0x00100000 /* Normal directory */
-#define DCACHE_AUTODIR_TYPE		0x00200000 /* Lookupless directory (presumed automount) */
-#define DCACHE_SYMLINK_TYPE		0x00300000 /* Symlink */
-#define DCACHE_FILE_TYPE		0x00400000 /* Other file type */
+#define DCACHE_MISS_TYPE		0x00000000 /* Negative dentry (maybe fallthru to nowhere) */
+#define DCACHE_WHITEOUT_TYPE		0x00100000 /* Whiteout dentry (stop pathwalk) */
+#define DCACHE_DIRECTORY_TYPE		0x00200000 /* Normal directory */
+#define DCACHE_AUTODIR_TYPE		0x00300000 /* Lookupless directory (presumed automount) */
+#define DCACHE_SYMLINK_TYPE		0x00400000 /* Symlink (or fallthru to such) */
+#define DCACHE_FILE_TYPE		0x00500000 /* Other file type (or fallthru to such) */
 
 #define DCACHE_MAY_FREE			0x00800000
 
@@ -423,6 +424,16 @@ static inline unsigned __d_entry_type(const struct dentry *dentry)
 	return dentry->d_flags & DCACHE_ENTRY_TYPE;
 }
 
+static inline bool d_is_miss(const struct dentry *dentry)
+{
+	return __d_entry_type(dentry) == DCACHE_MISS_TYPE;
+}
+
+static inline bool d_is_whiteout(const struct dentry *dentry)
+{
+	return __d_entry_type(dentry) == DCACHE_WHITEOUT_TYPE;
+}
+
 static inline bool d_can_lookup(const struct dentry *dentry)
 {
 	return __d_entry_type(dentry) == DCACHE_DIRECTORY_TYPE;
@@ -450,7 +461,8 @@ static inline bool d_is_file(const struct dentry *dentry)
 
 static inline bool d_is_negative(const struct dentry *dentry)
 {
-	return __d_entry_type(dentry) == DCACHE_MISS_TYPE;
+	// TODO: check d_is_whiteout(dentry) also.
+	return d_is_miss(dentry);
 }
 
 static inline bool d_is_positive(const struct dentry *dentry)