dlm: fix malfunction of dlm_tool caused by debugfs changes

With the current kernel, `dlm_tool lockdebug` fails as below:

"dlm_tool lockdebug ED0BD86DCE724393918A1AE8FDBF1EE3
can't open /sys/kernel/debug/dlm/ED0BD86DCE724393918A1AE8FDBF1EE3:
Operation not permitted"

This is because table_open() depends on file->f_op to tell which
seq_file ops should be passed down. But, the original file ops in
file->f_op is replaced by "debugfs_full_proxy_file_operations" with
commit 49d200deaa68 ("debugfs: prevent access to removed files'
private data").

Currently, I can think up 2 solutions: 1st, replace
debugfs_create_file() with debugfs_create_file_unsafe();
2nd, make different table_open#() accordingly. The 1st one
is neat, but I don't thoroughly understand its risk. Maybe
someone has a better one.

Signed-off-by: Eric Ren <zren@suse.com>
Signed-off-by: David Teigland <teigland@redhat.com>

fs/dlm/debug_fs.c

@@ -607,20 +607,54 @@ static const struct file_operations format2_fops;
 static const struct file_operations format3_fops;
 static const struct file_operations format4_fops;
 
-static int table_open(struct inode *inode, struct file *file)
+static int table_open1(struct inode *inode, struct file *file)
 {
 	struct seq_file *seq;
-	int ret = -1;
+	int ret;
 
-	if (file->f_op == &format1_fops)
-		ret = seq_open(file, &format1_seq_ops);
-	else if (file->f_op == &format2_fops)
-		ret = seq_open(file, &format2_seq_ops);
-	else if (file->f_op == &format3_fops)
-		ret = seq_open(file, &format3_seq_ops);
-	else if (file->f_op == &format4_fops)
-		ret = seq_open(file, &format4_seq_ops);
+	ret = seq_open(file, &format1_seq_ops);
+	if (ret)
+		return ret;
+
+	seq = file->private_data;
+	seq->private = inode->i_private; /* the dlm_ls */
+	return 0;
+}
+
+static int table_open2(struct inode *inode, struct file *file)
+{
+	struct seq_file *seq;
+	int ret;
+
+	ret = seq_open(file, &format2_seq_ops);
+	if (ret)
+		return ret;
+
+	seq = file->private_data;
+	seq->private = inode->i_private; /* the dlm_ls */
+	return 0;
+}
+
+static int table_open3(struct inode *inode, struct file *file)
+{
+	struct seq_file *seq;
+	int ret;
+
+	ret = seq_open(file, &format3_seq_ops);
+	if (ret)
+		return ret;
+
+	seq = file->private_data;
+	seq->private = inode->i_private; /* the dlm_ls */
+	return 0;
+}
+
+static int table_open4(struct inode *inode, struct file *file)
+{
+	struct seq_file *seq;
+	int ret;
 
+	ret = seq_open(file, &format4_seq_ops);
 	if (ret)
 		return ret;
 
@@ -631,7 +665,7 @@ static int table_open(struct inode *inode, struct file *file)
 
 static const struct file_operations format1_fops = {
 	.owner   = THIS_MODULE,
-	.open    = table_open,
+	.open    = table_open1,
 	.read    = seq_read,
 	.llseek  = seq_lseek,
 	.release = seq_release
@@ -639,7 +673,7 @@ static const struct file_operations format1_fops = {
 
 static const struct file_operations format2_fops = {
 	.owner   = THIS_MODULE,
-	.open    = table_open,
+	.open    = table_open2,
 	.read    = seq_read,
 	.llseek  = seq_lseek,
 	.release = seq_release
@@ -647,7 +681,7 @@ static const struct file_operations format2_fops = {
 
 static const struct file_operations format3_fops = {
 	.owner   = THIS_MODULE,
-	.open    = table_open,
+	.open    = table_open3,
 	.read    = seq_read,
 	.llseek  = seq_lseek,
 	.release = seq_release
@@ -655,7 +689,7 @@ static const struct file_operations format3_fops = {
 
 static const struct file_operations format4_fops = {
 	.owner   = THIS_MODULE,
-	.open    = table_open,
+	.open    = table_open4,
 	.read    = seq_read,
 	.llseek  = seq_lseek,
 	.release = seq_release