fs: rcu-walk aware d_revalidate method
Require filesystems be aware of .d_revalidate being called in rcu-walk
mode (nd->flags & LOOKUP_RCU). For now do a simple push down, returning
-ECHILD from all implementations.
Signed-off-by: Nick Piggin <npiggin@kernel.dk>
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 69b10ff..c936b49 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -863,6 +863,15 @@
dcache. Most filesystems leave this as NULL, because all their
dentries in the dcache are valid
+ d_revalidate may be called in rcu-walk mode (nd->flags & LOOKUP_RCU).
+ If in rcu-walk mode, the filesystem must revalidate the dentry without
+ blocking or storing to the dentry, d_parent and d_inode should not be
+ used without care (because they can go NULL), instead nd->inode should
+ be used.
+
+ If a situation is encountered that rcu-walk cannot handle, return
+ -ECHILD and it will be called again in ref-walk mode.
+
d_hash: called when the VFS adds a dentry to the hash table. The first
dentry passed to d_hash is the parent directory that the name is
to be hashed into. The inode is the dentry's inode.