f2fs: update several comments

Update several comments:
1. use f2fs_{un}lock_op install of mutex_{un}lock_op.
2. update comment of get_data_block().
3. update description of node offset.
Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/data.c

@@ -508,8 +508,8 @@ struct page *get_lock_data_page(struct inode *inode, pgoff_t index)
  * Caller ensures that this data page is never allocated.
  * A new zero-filled data page is allocated in the page cache.
  *
- * Also, caller should grab and release a mutex by calling mutex_lock_op() and
- * mutex_unlock_op().
+ * Also, caller should grab and release a rwsem by calling f2fs_lock_op() and
+ * f2fs_unlock_op().
  * Note that, npage is set only by make_empty_dir.
  */
 struct page *get_new_data_page(struct inode *inode,
@@ -595,10 +595,12 @@ static int __allocate_data_block(struct dnode_of_data *dn)
 }
 
 /*
- * This function should be used by the data read flow only where it
- * does not check the "create" flag that indicates block allocation.
- * The reason for this special functionality is to exploit VFS readahead
- * mechanism.
+ * get_data_block() now supported readahead/bmap/rw direct_IO with mapped bh.
+ * If original data blocks are allocated, then give them to blockdev.
+ * Otherwise,
+ *     a. preallocate requested block addresses
+ *     b. do not use extent cache for better performance
+ *     c. give the block addresses to blockdev
  */
 static int get_data_block(struct inode *inode, sector_t iblock,
 			struct buffer_head *bh_result, int create)

fs/f2fs/dir.c

@@ -432,8 +432,8 @@ static int room_for_filename(struct f2fs_dentry_block *dentry_blk, int slots)
 }
 
 /*
- * Caller should grab and release a mutex by calling mutex_lock_op() and
- * mutex_unlock_op().
+ * Caller should grab and release a rwsem by calling f2fs_lock_op() and
+ * f2fs_unlock_op().
  */
 int __f2fs_add_link(struct inode *dir, const struct qstr *name, struct inode *inode)
 {

fs/f2fs/f2fs.h

@@ -165,7 +165,7 @@ enum {
 	LOOKUP_NODE,			/* look up a node without readahead */
 	LOOKUP_NODE_RA,			/*
 					 * look up a node with readahead called
-					 * by get_datablock_ro.
+					 * by get_data_block.
 					 */
 };
 

fs/f2fs/node.c

@@ -393,8 +393,8 @@ static int get_node_path(struct f2fs_inode_info *fi, long block,
 
 /*
  * Caller should call f2fs_put_dnode(dn).
- * Also, it should grab and release a mutex by calling mutex_lock_op() and
- * mutex_unlock_op() only if ro is not set RDONLY_NODE.
+ * Also, it should grab and release a rwsem by calling f2fs_lock_op() and
+ * f2fs_unlock_op() only if ro is not set RDONLY_NODE.
  * In the case of RDONLY_NODE, we don't need to care about mutex.
  */
 int get_dnode_of_data(struct dnode_of_data *dn, pgoff_t index, int mode)
@@ -802,8 +802,8 @@ int truncate_xattr_node(struct inode *inode, struct page *page)
 }
 
 /*
- * Caller should grab and release a mutex by calling mutex_lock_op() and
- * mutex_unlock_op().
+ * Caller should grab and release a rwsem by calling f2fs_lock_op() and
+ * f2fs_unlock_op().
  */
 void remove_inode_page(struct inode *inode)
 {

fs/f2fs/node.h

@@ -224,7 +224,13 @@ static inline block_t next_blkaddr_of_node(struct page *node_page)
  *    |            `- direct node (5 + N => 5 + 2N - 1)
  *    `- double indirect node (5 + 2N)
  *                 `- indirect node (6 + 2N)
- *                       `- direct node (x(N + 1))
+ *                       `- direct node
+ *                 ......
+ *                 `- indirect node ((6 + 2N) + x(N + 1))
+ *                       `- direct node
+ *                 ......
+ *                 `- indirect node ((6 + 2N) + (N - 1)(N + 1))
+ *                       `- direct node
  */
 static inline bool IS_DNODE(struct page *node_page)
 {