Re: [PATCH 00/16 v3] tracing: Add new file system tracefs

[Steven Rostedt]

On Mon, 26 Jan 2015 15:44:19 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> Now what I could also do is to only allow this to be called once. And
> in that case, we can hard code what mkdir and rmdir are. This could
> work as currently there only exists a single instance of the instances
> directory.
> 
> I might just do that too.

And just did:

diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index c7eb4c58579e..13e17bf677f4 100644
--- a/fs/tracefs/inode.c
+++ b/fs/tracefs/inode.c
@@ -50,6 +50,11 @@ static const struct file_operations tracefs_file_operations = {
 	.llseek =	noop_llseek,
 };
 
+struct tracefs_dir_ops {
+	int (*mkdir)(const char *name);
+	int (*rmdir)(const char *name);
+};
+
 static char *get_dname(struct dentry *dentry)
 {
 	const char *dname;
@@ -67,13 +72,10 @@ static char *get_dname(struct dentry *dentry)
 
 static int tracefs_syscall_mkdir(struct inode *inode, struct dentry *dentry, umode_t mode)
 {
-	const struct tracefs_dir_ops *ops = inode ? inode->i_private : NULL;
+	const struct tracefs_dir_ops *ops = inode->i_private;
 	char *name;
 	int ret;
 
-	if (!ops)
-		return -EPERM;
-
 	name = get_dname(dentry);
 	if (!name)
 		return -ENOMEM;
@@ -98,9 +100,6 @@ static int tracefs_syscall_rmdir(struct inode *inode, struct dentry *dentry)
 	char *name;
 	int ret;
 
-	if (!ops)
-		return -EPERM;
-
 	name = get_dname(dentry);
 	if (!name)
 		return -ENOMEM;
@@ -317,16 +316,6 @@ static struct file_system_type trace_fs_type = {
 };
 MODULE_ALIAS_FS("tracefs");
 
-void tracefs_add_dir_ops(struct dentry *dentry, const struct tracefs_dir_ops *ops)
-{
-	struct inode *inode = dentry->d_inode;
-
-	if (!inode)
-		return;
-
-	inode->i_private = (void *)ops;
-}
-
 static struct dentry *start_creating(const char *name, struct dentry *parent)
 {
 	struct dentry *dentry;
@@ -425,6 +414,31 @@ struct dentry *tracefs_create_file(const char *name, umode_t mode,
 	return end_creating(dentry);
 }
 
+static struct dentry *__create_dir(const char *name, struct dentry *parent,
+				   const struct inode_operations *ops)
+{
+	struct dentry *dentry = start_creating(name, parent);
+	struct inode *inode;
+
+	if (IS_ERR(dentry))
+		return NULL;
+
+	inode = tracefs_get_inode(dentry->d_sb);
+	if (unlikely(!inode))
+		return failed_creating(dentry);
+
+	inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
+	inode->i_op = ops;
+	inode->i_fop = &simple_dir_operations;
+
+	/* directory inodes start off with i_nlink == 2 (for "." entry) */
+	inc_nlink(inode);
+	d_instantiate(dentry, inode);
+	inc_nlink(dentry->d_parent->d_inode);
+	fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
+	return end_creating(dentry);
+}
+
 /**
  * tracefs_create_dir - create a directory in the tracefs filesystem
  * @name: a pointer to a string containing the name of the directory to
@@ -444,26 +458,30 @@ struct dentry *tracefs_create_file(const char *name, umode_t mode,
  */
 struct dentry *tracefs_create_dir(const char *name, struct dentry *parent)
 {
-	struct dentry *dentry = start_creating(name, parent);
-	struct inode *inode;
+	return __create_dir(name, parent, &simple_dir_inode_operations);
+}
 
-	if (IS_ERR(dentry))
+struct dentry *tracefs_create_instance_dir(const char *name, struct dentry *parent,
+					  int (*mkdir)(const char *name),
+					  int (*rmdir)(const char *name))
+{
+	struct tracefs_dir_ops *dir_ops;
+	struct dentry *dentry;
+
+	dir_ops = kmalloc(sizeof(*dir_ops), GFP_KERNEL);
+	if (!dir_ops)
 		return NULL;
 
-	inode = tracefs_get_inode(dentry->d_sb);
-	if (unlikely(!inode))
-		return failed_creating(dentry);
+	dir_ops->mkdir = mkdir;
+	dir_ops->rmdir = mkdir;
 
-	inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
-	inode->i_op = &tracefs_dir_inode_operations;
-	inode->i_fop = &simple_dir_operations;
+	dentry = __create_dir(name, parent, &tracefs_dir_inode_operations);
+	if (!dentry)
+		return NULL;
 
-	/* directory inodes start off with i_nlink == 2 (for "." entry) */
-	inc_nlink(inode);
-	d_instantiate(dentry, inode);
-	inc_nlink(dentry->d_parent->d_inode);
-	fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
-	return end_creating(dentry);
+	dentry->d_inode->i_private = (void *)dir_ops;
+
+	return dentry;
 }
 
 static inline int tracefs_positive(struct dentry *dentry)
diff --git a/include/linux/tracefs.h b/include/linux/tracefs.h
index d142b1f9d453..5b727a17beee 100644
--- a/include/linux/tracefs.h
+++ b/include/linux/tracefs.h
@@ -34,12 +34,9 @@ struct dentry *tracefs_create_dir(const char *name, struct dentry *parent);
 void tracefs_remove(struct dentry *dentry);
 void tracefs_remove_recursive(struct dentry *dentry);
 
-struct tracefs_dir_ops {
-	int (*mkdir)(const char *name);
-	int (*rmdir)(const char *name);
-};
-
-void tracefs_add_dir_ops(struct dentry *dentry, const struct tracefs_dir_ops *ops);
+struct dentry *tracefs_create_instance_dir(const char *name, struct dentry *parent,
+					   int (*mkdir)(const char *name),
+					   int (*rmdir)(const char *name));
 
 bool tracefs_initialized(void);
 
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c555027c8aaf..2047501dcd16 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6445,18 +6445,13 @@ static int instance_rmdir(const char *name)
 	return ret;
 }
 
-static const struct tracefs_dir_ops instance_dir_ops = {
-	.mkdir		= instance_mkdir,
-	.rmdir		= instance_rmdir,
-};
-
 static __init void create_trace_instances(struct dentry *d_tracer)
 {
-	trace_instance_dir = tracefs_create_dir("instances", d_tracer);
+	trace_instance_dir = tracefs_create_instance_dir("instances", d_tracer,
+							 instance_mkdir,
+							 instance_rmdir);
 	if (WARN_ON(!trace_instance_dir))
 		return;
-
-	tracefs_add_dir_ops(trace_instance_dir, &instance_dir_ops);
 }
 
 static void
--
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