VFS: Add a fallthrough flag for marking virtual dentries

Add a DCACHE_FALLTHRU flag to indicate that, in a layered filesystem, this is
a virtual dentry that covers another one in a lower layer that should be used
instead.  This may be recorded on medium if directory integration is stored
there.

The flag can be set with d_set_fallthru() and tested with d_is_fallthru().

Original-author: Valerie Aurora <vaurora@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 9 insertions, 0 deletions

diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 98d2a948a08e..728f5d31b5e6 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -223,6 +223,7 @@ struct dentry_operations {
 #define DCACHE_FILE_TYPE                0x00500000 /* Other file type (or fallthru to such) */
 
 #define DCACHE_MAY_FREE                 0x00800000
+#define DCACHE_FALLTHRU                 0x01000000 /* Fall through to lower layer */
 
 extern seqlock_t rename_lock;
 
@@ -470,6 +471,14 @@ static inline bool d_is_positive(const struct dentry *dentry)
         return !d_is_negative(dentry);
 }
 
+extern void d_set_fallthru(struct dentry *dentry);
+
+static inline bool d_is_fallthru(const struct dentry *dentry)
+{
+        return dentry->d_flags & DCACHE_FALLTHRU;
+}
+
+
 extern int sysctl_vfs_cache_pressure;
 
 static inline unsigned long vfs_pressure_ratio(unsigned long val)