fs: icache RCU free inodes

[firefly-linux-kernel-4.4.55.git] / Documentation / filesystems / porting

diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
index b12c89538680aaf5f2cf3f5f872321f73a3d57ab..ccf0ce7866b9e057771da75b855be8ae08da69a6 100644 (file)
--- a/Documentation/filesystems/porting
+++ b/Documentation/filesystems/porting
@@ -216,7 +216,6 @@ had ->revalidate()) add calls in ->follow_link()/->readlink().
 ->d_parent changes are not protected by BKL anymore.  Read access is safe
 if at least one of the following is true:
        * filesystem has no cross-directory rename()
-       * dcache_lock is held
        * we know that parent had been locked (e.g. we are looking at
 ->d_parent of ->lookup() argument).
        * we are called from ->rename().
@@ -318,3 +317,46 @@ if it's zero is not *and* *never* *had* *been* enough.  Final unlink() and iput(
 may happen while the inode is in the middle of ->write_inode(); e.g. if you blindly
 free the on-disk inode, you may end up doing that while ->write_inode() is writing
 to it.
+
+---
+[mandatory]
+
+       .d_delete() now only advises the dcache as to whether or not to cache
+unreferenced dentries, and is now only called when the dentry refcount goes to
+0. Even on 0 refcount transition, it must be able to tolerate being called 0,
+1, or more times (eg. constant, idempotent).
+
+---
+[mandatory]
+
+       .d_compare() calling convention and locking rules are significantly
+changed. Read updated documentation in Documentation/filesystems/vfs.txt (and
+look at examples of other filesystems) for guidance.
+
+---
+[mandatory]
+
+       .d_hash() calling convention and locking rules are significantly
+changed. Read updated documentation in Documentation/filesystems/vfs.txt (and
+look at examples of other filesystems) for guidance.
+
+---
+[mandatory]
+       dcache_lock is gone, replaced by fine grained locks. See fs/dcache.c
+for details of what locks to replace dcache_lock with in order to protect
+particular things. Most of the time, a filesystem only needs ->d_lock, which
+protects *all* the dcache state of a given dentry.
+
+--
+[mandatory]
+
+       Filesystems must RCU-free their inodes, if they can have been accessed
+via rcu-walk path walk (basically, if the file can have had a path name in the
+vfs namespace).
+
+       i_dentry and i_rcu share storage in a union, and the vfs expects
+i_dentry to be reinitialized before it is freed, so an:
+
+  INIT_LIST_HEAD(&inode->i_dentry);
+
+must be done in the RCU callback.