1 files changed, 13 insertions, 0 deletions

diff --git a/fs/udf/udf_i.h b/fs/udf/udf_i.h
index e58d1de41073..d1bd31ea724e 100644
--- a/fs/udf/udf_i.h
+++ b/fs/udf/udf_i.h
@@ -1,6 +1,18 @@
 #ifndef _UDF_I_H
 #define _UDF_I_H
 
+/*
+ * The i_data_sem and i_mutex serve for protection of allocation information
+ * of a regular files and symlinks. This includes all extents belonging to
+ * the file/symlink, a fact whether data are in-inode or in external data
+ * blocks, preallocation, goal block information... When extents are read,
+ * i_mutex or i_data_sem must be held (for reading is enough in case of
+ * i_data_sem). When extents are changed, i_data_sem must be held for writing
+ * and also i_mutex must be held.
+ *
+ * For directories i_mutex is used for all the necessary protection.
+ */
+
 struct udf_inode_info {
         struct timespec         i_crtime;
         /* Physical address of inode */
@@ -21,6 +33,7 @@ struct udf_inode_info {
                 struct long_ad          *i_lad;
                 __u8            *i_data;
         } i_ext;
+        struct rw_semaphore     i_data_sem;
         struct inode vfs_inode;
 };