[RFC][PATCH 1/4] Prepare i_mutex lockdep subclasses for locking of variable path lengths

[Louis Rilling <Louis.Rilling@kerlabs.com>]

[-- Attachment #1: prepare-variable-path-lengths-inode-locking.patch --]
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Some filesystems, like configfs, need to lock more than two regular inodes
recursively in a tree, which i_mutex lockdep subclasses do not permit.

This patch reorders the definitions (but not the semantics) of i_mutex lockdep
sub-classes so that nested i_mutex locking can be done with sub-classes
I_MUTEX_PARENT -> I_MUTEX_CHILD -> I_MUTEX_CHILD + 1 -> I_MUTEX_CHILD + 2 -> ...
until MAX_LOCKDEP_SUBCLASSES - 1.

Signed-off-by: Louis Rilling <Louis.Rilling@kerlabs.com>
---
 include/linux/fs.h |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)


Index: b/include/linux/fs.h
===================================================================
--- a/include/linux/fs.h	2008-05-21 09:40:28.000000000 +0200
+++ b/include/linux/fs.h	2008-05-22 12:20:20.000000000 +0200
@@ -660,20 +660,23 @@ struct inode {
  * inode->i_mutex nesting subclasses for the lock validator:
  *
  * 0: the object of the current VFS operation
- * 1: parent
- * 2: child/target
- * 3: quota file
+ * 1: xattrs
+ * 2: quota file
+ * 3: parent
+ * 4: child/target
+ * ...: lower-level children
  *
  * The locking order between these classes is
- * parent -> child -> normal -> xattr -> quota
+ * parent -> child -> sub-children... -> normal -> xattr -> quota
  */
 enum inode_i_mutex_lock_class
 {
 	I_MUTEX_NORMAL,
+	I_MUTEX_XATTR,
+	I_MUTEX_QUOTA,
 	I_MUTEX_PARENT,
 	I_MUTEX_CHILD,
-	I_MUTEX_XATTR,
-	I_MUTEX_QUOTA
+	/* Reserved for variable paths of nested inode locks */
 };
 
 extern void inode_double_lock(struct inode *inode1, struct inode *inode2);

-- 
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