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, 12 insertions, 0 deletions

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 6dabc4a10396..b6f5ddab66bf 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -97,6 +97,18 @@ EXPORT_SYMBOL_GPL(debugfs_use_file_finish);
 
 #define F_DENTRY(filp) ((filp)->f_path.dentry)
 
+const struct file_operations *debugfs_real_fops(const struct file *filp)
+	__must_hold(&debugfs_srcu)
+{
+	struct debugfs_fsdata *fsd = F_DENTRY(filp)->d_fsdata;
+	/*
+	 * Neither the pointer to the struct file_operations, nor its
+	 * contents ever change -- srcu_dereference() is not needed here.
+	 */
+	return fsd->real_fops;
+}
+EXPORT_SYMBOL_GPL(debugfs_real_fops);
+
 static int open_proxy_open(struct inode *inode, struct file *filp)
 {
 	const struct dentry *dentry = F_DENTRY(filp);