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, 19 insertions, 3 deletions

diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index c59f015f386e..a9c3d3e9af39 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -185,6 +185,11 @@ static const struct super_operations debugfs_super_operations = {
 	.evict_inode	= debugfs_evict_inode,
 };
 
+static void debugfs_release_dentry(struct dentry *dentry)
+{
+	kfree(dentry->d_fsdata);
+}
+
 static struct vfsmount *debugfs_automount(struct path *path)
 {
 	debugfs_automount_t f;
@@ -194,6 +199,7 @@ static struct vfsmount *debugfs_automount(struct path *path)
 
 static const struct dentry_operations debugfs_dops = {
 	.d_delete = always_delete_dentry,
+	.d_release = debugfs_release_dentry,
 	.d_automount = debugfs_automount,
 };
 
@@ -341,24 +347,34 @@ static struct dentry *__debugfs_create_file(const char *name, umode_t mode,
 {
 	struct dentry *dentry;
 	struct inode *inode;
+	struct debugfs_fsdata *fsd;
+
+	fsd = kmalloc(sizeof(*fsd), GFP_KERNEL);
+	if (!fsd)
+		return NULL;
 
 	if (!(mode & S_IFMT))
 		mode |= S_IFREG;
 	BUG_ON(!S_ISREG(mode));
 	dentry = start_creating(name, parent);
 
-	if (IS_ERR(dentry))
+	if (IS_ERR(dentry)) {
+		kfree(fsd);
 		return NULL;
+	}
 
 	inode = debugfs_get_inode(dentry->d_sb);
-	if (unlikely(!inode))
+	if (unlikely(!inode)) {
+		kfree(fsd);
 		return failed_creating(dentry);
+	}
 
 	inode->i_mode = mode;
 	inode->i_private = data;
 
 	inode->i_fop = proxy_fops;
-	dentry->d_fsdata = (void *)real_fops;
+	fsd->real_fops = real_fops;
+	dentry->d_fsdata = fsd;
 
 	d_instantiate(dentry, inode);
 	fsnotify_create(d_inode(dentry->d_parent), dentry);