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-rw-r--r--Documentation/filesystems/porting53
1 files changed, 53 insertions, 0 deletions
diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
index f1b87d8aa2da..46f3bb7a02f5 100644
--- a/Documentation/filesystems/porting
+++ b/Documentation/filesystems/porting
@@ -525,3 +525,56 @@ in your dentry operations instead.
set_delayed_call() where it used to set *cookie.
->put_link() is gone - just give the destructor to set_delayed_call()
in ->get_link().
+--
+[mandatory]
+ ->getxattr() and xattr_handler.get() get dentry and inode passed separately.
+ dentry might be yet to be attached to inode, so do _not_ use its ->d_inode
+ in the instances. Rationale: !@#!@# security_d_instantiate() needs to be
+ called before we attach dentry to inode.
+--
+[mandatory]
+ symlinks are no longer the only inodes that do *not* have i_bdev/i_cdev/
+ i_pipe/i_link union zeroed out at inode eviction. As the result, you can't
+ assume that non-NULL value in ->i_nlink at ->destroy_inode() implies that
+ it's a symlink. Checking ->i_mode is really needed now. In-tree we had
+ to fix shmem_destroy_callback() that used to take that kind of shortcut;
+ watch out, since that shortcut is no longer valid.
+--
+[mandatory]
+ ->i_mutex is replaced with ->i_rwsem now. inode_lock() et.al. work as
+ they used to - they just take it exclusive. However, ->lookup() may be
+ called with parent locked shared. Its instances must not
+ * use d_instantiate) and d_rehash() separately - use d_add() or
+ d_splice_alias() instead.
+ * use d_rehash() alone - call d_add(new_dentry, NULL) instead.
+ * in the unlikely case when (read-only) access to filesystem
+ data structures needs exclusion for some reason, arrange it
+ yourself. None of the in-tree filesystems needed that.
+ * rely on ->d_parent and ->d_name not changing after dentry has
+ been fed to d_add() or d_splice_alias(). Again, none of the
+ in-tree instances relied upon that.
+ We are guaranteed that lookups of the same name in the same directory
+ will not happen in parallel ("same" in the sense of your ->d_compare()).
+ Lookups on different names in the same directory can and do happen in
+ parallel now.
+--
+[recommended]
+ ->iterate_shared() is added; it's a parallel variant of ->iterate().
+ Exclusion on struct file level is still provided (as well as that
+ between it and lseek on the same struct file), but if your directory
+ has been opened several times, you can get these called in parallel.
+ Exclusion between that method and all directory-modifying ones is
+ still provided, of course.
+
+ Often enough ->iterate() can serve as ->iterate_shared() without any
+ changes - it is a read-only operation, after all. If you have any
+ per-inode or per-dentry in-core data structures modified by ->iterate(),
+ you might need something to serialize the access to them. If you
+ do dcache pre-seeding, you'll need to switch to d_alloc_parallel() for
+ that; look for in-tree examples.
+
+ Old method is only used if the new one is absent; eventually it will
+ be removed. Switch while you still can; the old one won't stay.
+--
+[mandatory]
+ ->atomic_open() calls without O_CREAT may happen in parallel.