1 files changed, 36 insertions, 4 deletions

diff --git a/include/fuse_lowlevel.h b/include/fuse_lowlevel.h
index cceb9be..6bad70e 100644
--- a/include/fuse_lowlevel.h
+++ b/include/fuse_lowlevel.h
@@ -127,6 +127,15 @@ struct fuse_forget_data {
 	uint64_t nlookup;
 };
 
+/**
+ * Flags for fuse_lowlevel_notify_expire_entry()
+ * 0 = invalidate entry
+ * FUSE_LL_EXPIRE_ONLY = expire entry
+*/
+enum fuse_expire_flags {
+	FUSE_LL_EXPIRE_ONLY	= (1 << 0),
+};
+
 /* 'to_set' flags in setattr */
 #define FUSE_SET_ATTR_MODE	(1 << 0)
 #define FUSE_SET_ATTR_UID	(1 << 1)
@@ -1675,10 +1684,33 @@ int fuse_lowlevel_notify_inval_inode(struct fuse_session *se, fuse_ino_t ino,
 int fuse_lowlevel_notify_inval_entry(struct fuse_session *se, fuse_ino_t parent,
 				     const char *name, size_t namelen);
 
-enum fuse_expire_flags {
-	FUSE_LL_EXPIRE_ONLY	= (1 << 0),
-};
-
+/**
+ * Notify to expire or invalidate parent attributes and the dentry 
+ * matching parent/name
+ * 
+ * Underlying function for fuse_lowlevel_notify_inval_entry().
+ * 
+ * In addition to invalidating an entry, it also allows to expire an entry.
+ * In that case, the entry is not forcefully removed from kernel cache 
+ * but instead the next access to it forces a lookup from the filesystem.
+ * 
+ * This makes a difference for overmounted dentries, where plain invalidation
+ * would detach all submounts before dropping the dentry from the cache. 
+ * If only expiry is set on the dentry, then any overmounts are left alone and
+ * until ->d_revalidate() is called.
+ * 
+ * Note: ->d_revalidate() is not called for the case of following a submount,
+ * so invalidation will only be triggered for the non-overmounted case.
+ * The dentry could also be mounted in a different mount instance, in which case
+ * any submounts will still be detached.
+ *
+ * @param se the session object
+ * @param parent inode number
+ * @param name file name
+ * @param namelen strlen() of file name
+ * @param flags flags to control if the entry should be expired or invalidated
+ * @return zero for success, -errno for failure
+*/
 int fuse_lowlevel_notify_expire_entry(struct fuse_session *se, fuse_ino_t parent,
                                       const char *name, size_t namelen,
                                       enum fuse_expire_flags flags);