Adding eventfs_file structure which will hold properties of file or dir.

Adding following functions to add dir in eventfs:

eventfs_create_events_dir() will directly create events dir with-in
tracing folder.

eventfs_add_subsystem_dir() will adds the info of subsystem_dir to
eventfs and dynamically create subsystem_dir as and when requires.

eventfs_add_dir() will add the info of dir (which is with-in
subsystem_dir) to eventfs and dynamically create these dir as
and when requires.

Signed-off-by: Ajay Kaher <redacted>
Co-developed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Tested-by: Ching-lin Yu <redacted>
---
  fs/tracefs/Makefile      |   1 +
  fs/tracefs/event_inode.c | 252 +++++++++++++++++++++++++++++++++++++++
  include/linux/tracefs.h  |  29 +++++
  kernel/trace/trace.h     |   1 +
  4 files changed, 283 insertions(+)
  create mode 100644 fs/tracefs/event_inode.c

diff --git a/fs/tracefs/Makefile b/fs/tracefs/Makefile
index 7c35a282b..73c56da8e 100644
--- a/fs/tracefs/Makefile
+++ b/fs/tracefs/Makefile

@@ -1,5 +1,6 @@
  # SPDX-License-Identifier: GPL-2.0-only
  tracefs-objs	:= inode.o
+tracefs-objs	+= event_inode.o
  
  obj-$(CONFIG_TRACING)	+= tracefs.o
  

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
new file mode 100644
index 000000000..82caba7e9
--- /dev/null
+++ b/fs/tracefs/event_inode.c

@@ -0,0 +1,252 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  event_inode.c - part of tracefs, a pseudo file system for activating tracing
+ *
+ *  Copyright (C) 2020-22 VMware Inc, author: Steven Rostedt (VMware) <rostedt@goodmis.org>
+ *  Copyright (C) 2020-22 VMware Inc, author: Ajay Kaher <akaher@vmware.com>
+ *
+ *  eventfs is used to show trace events with one set of dentries
+ *
+ *  eventfs stores meta-data of files/dirs and skip to create object of
+ *  inodes/dentries. As and when requires, eventfs will create the
+ *  inodes/dentries for only required files/directories. Also eventfs
+ *  would delete the inodes/dentries once no more requires but preserve
+ *  the meta data.
+ */
+#include <linux/fsnotify.h>
+#include <linux/fs.h>
+#include <linux/namei.h>
+#include <linux/security.h>
+#include <linux/tracefs.h>
+#include <linux/kref.h>
+#include <linux/delay.h>
+#include "internal.h"
+
+/**
+ * eventfs_dentry_to_rwsem - Return corresponding eventfs_rwsem
+ * @dentry: a pointer to dentry
+ *
+ * helper function to return crossponding eventfs_rwsem for given dentry
+ */
+static struct rw_semaphore *eventfs_dentry_to_rwsem(struct dentry *dentry)
+{
+	if (S_ISDIR(dentry->d_inode->i_mode))
+		return (struct rw_semaphore *)dentry->d_inode->i_private;
+	else
+		return (struct rw_semaphore *)dentry->d_parent->d_inode->i_private;
+}
+
+/**
+ * eventfs_down_read - acquire read lock function
+ * @eventfs_rwsem: a pointer to rw_semaphore
+ *
+ * helper function to perform read lock, skip locking if caller task already
+ * own the lock. read lock requires for lookup(), release() and these also
+ * called with-in open(), remove() which already hold the read/write lock.
+ */
+static void eventfs_down_read(struct rw_semaphore *eventfs_rwsem)
+{
+	down_read_nested(eventfs_rwsem, SINGLE_DEPTH_NESTING);
+}
+
+/**
+ * eventfs_up_read - release read lock function
+ * @eventfs_rwsem: a pointer to rw_semaphore
+ *
+ * helper function to release eventfs_rwsem lock if locked
+ */
+static void eventfs_up_read(struct rw_semaphore *eventfs_rwsem)
+{
+	up_read(eventfs_rwsem);
+}
+
+/**
+ * eventfs_down_write - acquire write lock function
+ * @eventfs_rwsem: a pointer to rw_semaphore
+ *
+ * helper function to perform write lock on eventfs_rwsem
+ */
+static void eventfs_down_write(struct rw_semaphore *eventfs_rwsem)
+{
+	while (!down_write_trylock(eventfs_rwsem))
+		msleep(10);
+}
+
+/**
+ * eventfs_up_write - release write lock function
+ * @eventfs_rwsem: a pointer to rw_semaphore
+ *
+ * helper function to perform write lock on eventfs_rwsem
+ */
+static void eventfs_up_write(struct rw_semaphore *eventfs_rwsem)
+{
+	up_write(eventfs_rwsem);
+}
+
+static const struct file_operations eventfs_file_operations = {
+};
+
+static const struct inode_operations eventfs_root_dir_inode_operations = {
+};
+
+/**
+ * eventfs_create_events_dir - create the trace event structure
+ * @name: a pointer to a string containing the name of the directory to
+ *        create.
+ * @parent: a pointer to the parent dentry for this file.  This should be a
+ *          directory dentry if set.  If this parameter is NULL, then the
+ *          directory will be created in the root of the tracefs filesystem.
+ * @eventfs_rwsem: a pointer to rw_semaphore
+ *
+ * This function creates the top of the trace event directory.
+ */
+struct dentry *eventfs_create_events_dir(const char *name,
+					 struct dentry *parent,
+					 struct rw_semaphore *eventfs_rwsem)
+{
+	struct dentry *dentry = tracefs_start_creating(name, parent);
+	struct eventfs_inode *ei;
+	struct tracefs_inode *ti;
+	struct inode *inode;
+
+	if (IS_ERR(dentry))
+		return dentry;
+
+	ei = kzalloc(sizeof(*ei), GFP_KERNEL);
+	if (!ei)
+		return ERR_PTR(-ENOMEM);
+	inode = tracefs_get_inode(dentry->d_sb);
+	if (unlikely(!inode)) {
+		kfree(ei);
+		tracefs_failed_creating(dentry);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	init_rwsem(eventfs_rwsem);
+	INIT_LIST_HEAD(&ei->e_top_files);
+
+	ti = get_tracefs(inode);
+	ti->flags |= TRACEFS_EVENT_INODE;
+	ti->private = ei;
+
+	inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
+	inode->i_op = &eventfs_root_dir_inode_operations;
+	inode->i_fop = &eventfs_file_operations;
+	inode->i_private = eventfs_rwsem;
+
+	/* 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 tracefs_end_creating(dentry);
+}
+
+/**
+ * eventfs_add_subsystem_dir - add eventfs subsystem_dir to list to create later
+ * @name: a pointer to a string containing the name of the file to create.
+ * @parent: a pointer to the parent dentry for this dir.
+ * @eventfs_rwsem: a pointer to rw_semaphore
+ *
+ * This function adds eventfs subsystem dir to list.
+ * And all these dirs are created on the fly when they are looked up,
+ * and the dentry and inodes will be removed when they are done.
+ */
+struct eventfs_file *eventfs_add_subsystem_dir(const char *name,
+					       struct dentry *parent,
+					       struct rw_semaphore *eventfs_rwsem)
+{
+	struct tracefs_inode *ti_parent;
+	struct eventfs_inode *ei_parent;
+	struct eventfs_file *ef;
+
+	if (!parent)
+		return ERR_PTR(-EINVAL);
+
+	ti_parent = get_tracefs(parent->d_inode);
+	ei_parent = ti_parent->private;
+
+	ef = kzalloc(sizeof(*ef), GFP_KERNEL);
+	if (!ef)
+		return ERR_PTR(-ENOMEM);
+
+	ef->ei = kzalloc(sizeof(*ef->ei), GFP_KERNEL);
+	if (!ef->ei) {
+		kfree(ef);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	INIT_LIST_HEAD(&ef->ei->e_top_files);
+
+	ef->name = kstrdup(name, GFP_KERNEL);
+	if (!ef->name) {
+		kfree(ef->ei);
+		kfree(ef);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	ef->mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
+	ef->iop = &eventfs_root_dir_inode_operations;
+	ef->fop =  &eventfs_file_operations;
+	ef->dentry = NULL;
+	ef->created = false;
+	ef->d_parent = parent;
+	ef->data = eventfs_rwsem;
+
+	eventfs_down_write(eventfs_rwsem);
+	list_add_tail(&ef->list, &ei_parent->e_top_files);
+	eventfs_up_write(eventfs_rwsem);
+	return ef;
+}
+
+/**
+ * eventfs_add_dir - add eventfs dir to list to create later
+ * @name: a pointer to a string containing the name of the file to create.
+ * @ef_parent: a pointer to the parent eventfs_file for this dir.
+ * @eventfs_rwsem: a pointer to rw_semaphore
+ *
+ * This function adds eventfs dir to list.
+ * And all these dirs are created on the fly when they are looked up,
+ * and the dentry and inodes will be removed when they are done.
+ */
+struct eventfs_file *eventfs_add_dir(const char *name,
+				     struct eventfs_file *ef_parent,
+				     struct rw_semaphore *eventfs_rwsem)
+{
+	struct eventfs_file *ef;
+
+	if (!ef_parent)
+		return ERR_PTR(-EINVAL);
+
+	ef = kzalloc(sizeof(*ef), GFP_KERNEL);
+	if (!ef)
+		return ERR_PTR(-ENOMEM);
+
+	ef->ei = kzalloc(sizeof(*ef->ei), GFP_KERNEL);
+	if (!ef->ei) {
+		kfree(ef);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	INIT_LIST_HEAD(&ef->ei->e_top_files);
+
+	ef->name = kstrdup(name, GFP_KERNEL);
+	if (!ef->name) {
+		kfree(ef->ei);
+		kfree(ef);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	ef->mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
+	ef->iop = &eventfs_root_dir_inode_operations;
+	ef->fop =  &eventfs_file_operations;
+	ef->created = false;
+	ef->dentry = NULL;
+	ef->d_parent = NULL;
+	ef->data = eventfs_rwsem;
+
+	eventfs_down_write(eventfs_rwsem);
+	list_add_tail(&ef->list, &ef_parent->ei->e_top_files);
+	eventfs_up_write(eventfs_rwsem);
+	return ef;
+}

diff --git a/include/linux/tracefs.h b/include/linux/tracefs.h
index 999124459..aeca6761f 100644
--- a/include/linux/tracefs.h
+++ b/include/linux/tracefs.h

@@ -21,6 +21,35 @@ struct file_operations;
  
  #ifdef CONFIG_TRACING
  
+struct eventfs_inode {
+	struct list_head		e_top_files;
+};
+
+struct eventfs_file {
+	const char                      *name;
+	struct dentry                   *d_parent;
+	struct dentry                   *dentry;
+	struct list_head                list;
+	struct eventfs_inode            *ei;
+	const struct file_operations    *fop;
+	const struct inode_operations   *iop;
+	void                            *data;
+	umode_t                         mode;
+	bool                            created;
+};
+
+struct dentry *eventfs_create_events_dir(const char *name,
+					 struct dentry *parent,
+					 struct rw_semaphore *eventfs_rwsem);
+
+struct eventfs_file *eventfs_add_subsystem_dir(const char *name,
+					       struct dentry *parent,
+					       struct rw_semaphore *eventfs_rwsem);
+
+struct eventfs_file *eventfs_add_dir(const char *name,
+				     struct eventfs_file *ef_parent,
+				     struct rw_semaphore *eventfs_rwsem);
+
  struct dentry *tracefs_create_file(const char *name, umode_t mode,
  				   struct dentry *parent, void *data,
  				   const struct file_operations *fops);

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 616e1aa1c..3726725c8 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h

@@ -359,6 +359,7 @@ struct trace_array {
  	struct dentry		*options;
  	struct dentry		*percpu_dir;
  	struct dentry		*event_dir;
+	struct rw_semaphore     eventfs_rwsem;
  	struct trace_options	*topts;
  	struct list_head	systems;
  	struct list_head	events;