debugfs: add support for more elaborate ->d_fsdata

Currently, the user provided fops, "real_fops", are stored directly into
->d_fsdata.

In order to be able to store more per-file state and thus prepare for more
granular file removal protection, wrap the real_fops into a dynamically
allocated container struct, debugfs_fsdata.

A struct debugfs_fsdata gets allocated at file creation and freed from the
newly intoduced ->d_release().

Finally, move the implementation of debugfs_real_fops() out of the public
debugfs header such that struct debugfs_fsdata's declaration can be kept
private.

Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 3 insertions, 17 deletions

diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
index b93efc8feecd..cbee5f4a02a3 100644
--- a/include/linux/debugfs.h
+++ b/include/linux/debugfs.h
@@ -45,23 +45,6 @@ extern struct dentry *arch_debugfs_dir;
 
 extern struct srcu_struct debugfs_srcu;
 
-/**
- * debugfs_real_fops - getter for the real file operation
- * @filp: a pointer to a struct file
- *
- * Must only be called under the protection established by
- * debugfs_use_file_start().
- */
-static inline const struct file_operations *debugfs_real_fops(const struct file *filp)
-	__must_hold(&debugfs_srcu)
-{
-	/*
-	 * Neither the pointer to the struct file_operations, nor its
-	 * contents ever change -- srcu_dereference() is not needed here.
-	 */
-	return filp->f_path.dentry->d_fsdata;
-}
-
 #define DEFINE_DEBUGFS_ATTRIBUTE(__fops, __get, __set, __fmt)		\
 static int __fops ## _open(struct inode *inode, struct file *file)	\
 {									\
@@ -112,6 +95,9 @@ int debugfs_use_file_start(const struct dentry *dentry, int *srcu_idx)
 
 void debugfs_use_file_finish(int srcu_idx) __releases(&debugfs_srcu);
 
+const struct file_operations *debugfs_real_fops(const struct file *filp)
+	__must_hold(&debugfs_srcu);
+
 ssize_t debugfs_attr_read(struct file *file, char __user *buf,
 			size_t len, loff_t *ppos);
 ssize_t debugfs_attr_write(struct file *file, const char __user *buf,