From:   Ajay Kaher <akaher@vmware.com>
To:     rostedt@goodmis.org, mhiramat@kernel.org
Cc:     linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
        chinglinyu@google.com, namit@vmware.com, srivatsab@vmware.com,
        srivatsa@csail.mit.edu, amakhalov@vmware.com,
        vsirnapalli@vmware.com, tkundu@vmware.com, er.ajay.kaher@gmail.com,
        Ajay Kaher <akaher@vmware.com>
Subject: [PATCH 5/8] eventfs: adding functions to create eventfs files and directories
Date:   Sun, 22 Jan 2023 22:37:04 +0530
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Adding eventfs_create_file(), eventfs_create_dir()
to create file, dir at runtime as and when requires.

These function will be called either from lookup
of inode_operations or open of file_operations.

Signed-off-by: Ajay Kaher <akaher@vmware.com>
Co-developed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Tested-by: Ching-lin Yu <chinglinyu@google.com>
---
 fs/tracefs/event_inode.c | 137 ++++++++++++++++++++++++++++++++++++++++++++++-
 fs/tracefs/inode.c       |  47 ++++++++++++++++
 include/linux/tracefs.h  |   6 +++
 3 files changed, 189 insertions(+), 1 deletion(-)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 4d47da0..28866c0 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -21,6 +21,141 @@
 #include <linux/kref.h>
 #include "internal.h"
 
+/**
+ * eventfs_create_file - create a file in the tracefs filesystem
+ * @name: a pointer to a string containing the name of the file to create.
+ * @mode: the permission that the file should have.
+ * @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
+ *          file will be created in the root of the tracefs filesystem.
+ * @data: a pointer to something that the caller will want to get to later
+ *        on.  The inode.i_private pointer will point to this value on
+ *        the open() call.
+ * @fops: a pointer to a struct file_operations that should be used for
+ *        this file.
+ *
+ * This is the basic "create a file" function for tracefs.  It allows for a
+ * wide range of flexibility in creating a file.
+ *
+ * This function will return a pointer to a dentry if it succeeds.  This
+ * pointer must be passed to the tracefs_remove() function when the file is
+ * to be removed (no automatic cleanup happens if your module is unloaded,
+ * you are responsible here.)  If an error occurs, %NULL will be returned.
+ *
+ * If tracefs is not enabled in the kernel, the value -%ENODEV will be
+ * returned.
+ */
+struct dentry *eventfs_create_file(const char *name, umode_t mode,
+				   struct dentry *parent, void *data,
+				   const struct file_operations *fop,
+				   bool anon)
+{
+	struct tracefs_inode *ti;
+	struct dentry *dentry;
+	struct inode *inode;
+
+	if (security_locked_down(LOCKDOWN_TRACEFS))
+		return NULL;
+
+	if (!(mode & S_IFMT))
+		mode |= S_IFREG;
+
+	if (WARN_ON_ONCE(!S_ISREG(mode)))
+		return NULL;
+
+	dentry = eventfs_start_creating(name, parent);
+
+	if (IS_ERR(dentry))
+		return dentry;
+
+	inode = tracefs_get_inode(dentry->d_sb);
+	if (unlikely(!inode))
+		return eventfs_failed_creating(dentry);
+
+	inode->i_mode = mode;
+	inode->i_fop = fop;
+	inode->i_private = data;
+
+	ti = get_tracefs(inode);
+	ti->flags |= TRACEFS_EVENT_INODE;
+
+	if (anon)
+		d_instantiate_anon(dentry, inode);
+	else
+		d_instantiate(dentry, inode);
+
+	fsnotify_create(dentry->d_parent->d_inode, dentry);
+	return eventfs_end_creating(dentry);
+}
+
+/**
+ * eventfs_create_dir - create a dir in the tracefs filesystem
+ * @name: a pointer to a string containing the name of the file to create.
+ * @mode: the permission that the file should have.
+ * @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
+ *          file will be created in the root of the tracefs filesystem.
+ * @data: a pointer to something that the caller will want to get to later
+ *        on.  The inode.i_private pointer will point to this value on
+ *        the open() call.
+ * @fop: a pointer to a struct file_operations that should be used for
+ *        this dir.
+ * @iop: a pointer to a struct inode_operations that should be used for
+ *        this dir.
+ *
+ * This is the basic "create a dir" function for eventfs.  It allows for a
+ * wide range of flexibility in creating a dir.
+ *
+ * This function will return a pointer to a dentry if it succeeds.  This
+ * pointer must be passed to the tracefs_remove() function when the file is
+ * to be removed (no automatic cleanup happens if your module is unloaded,
+ * you are responsible here.)  If an error occurs, %NULL will be returned.
+ *
+ * If tracefs is not enabled in the kernel, the value -%ENODEV will be
+ * returned.
+ */
+struct dentry *eventfs_create_dir(const char *name, umode_t mode,
+				  struct dentry *parent, void *data,
+				  const struct file_operations *fop,
+				  const struct inode_operations *iop,
+				  bool anon)
+{
+	struct tracefs_inode *ti;
+	struct dentry *dentry;
+	struct inode *inode;
+
+	if (security_locked_down(LOCKDOWN_TRACEFS))
+		return NULL;
+
+	WARN_ON(!S_ISDIR(mode));
+
+	dentry = eventfs_start_creating(name, parent);
+
+	if (IS_ERR(dentry))
+		return dentry;
+
+	inode = tracefs_get_inode(dentry->d_sb);
+	if (unlikely(!inode))
+		return eventfs_failed_creating(dentry);
+
+	inode->i_mode = mode;
+	inode->i_op = iop;
+	inode->i_fop = fop;
+	inode->i_private = data;
+
+	ti = get_tracefs(inode);
+	ti->flags |= TRACEFS_EVENT_INODE;
+
+	inc_nlink(inode);
+	if (anon)
+		d_instantiate_anon(dentry, inode);
+	else
+		d_instantiate(dentry, inode);
+	inc_nlink(dentry->d_parent->d_inode);
+	fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
+	return eventfs_end_creating(dentry);
+}
+
 static const struct file_operations eventfs_file_operations = {
 };
 
@@ -86,9 +221,9 @@ struct dentry *eventfs_create_events_dir(const char *name, struct dentry *parent
  */
 struct eventfs_file *eventfs_add_subsystem_dir(const char *name, struct dentry *parent)
 {
-	struct eventfs_file *ef;
 	struct tracefs_inode *ti_parent;
 	struct eventfs_inode *ei_parent;
+	struct eventfs_file *ef;
 
 	if (!parent)
 		return ERR_PTR(-EINVAL);
diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index 015b7b8..6d950d1 100644
--- a/fs/tracefs/inode.c
+++ b/fs/tracefs/inode.c
@@ -451,6 +451,53 @@ struct dentry *tracefs_end_creating(struct dentry *dentry)
 	return dentry;
 }
 
+struct dentry *eventfs_start_creating(const char *name, struct dentry *parent)
+{
+	struct dentry *dentry;
+	int error;
+
+	error = simple_pin_fs(&trace_fs_type, &tracefs_mount,
+			      &tracefs_mount_count);
+	if (error)
+		return ERR_PTR(error);
+
+	/*
+	 * If the parent is not specified, we create it in the root.
+	 * We need the root dentry to do this, which is in the super
+	 * block. A pointer to that is in the struct vfsmount that we
+	 * have around.
+	 */
+	if (!parent)
+		parent = tracefs_mount->mnt_root;
+
+	if (unlikely(IS_DEADDIR(parent->d_inode)))
+		dentry = ERR_PTR(-ENOENT);
+	else
+		dentry = lookup_one_len(name, parent, strlen(name));
+
+	if (!IS_ERR(dentry) && dentry->d_inode) {
+		dput(dentry);
+		dentry = ERR_PTR(-EEXIST);
+	}
+
+	if (IS_ERR(dentry))
+		simple_release_fs(&tracefs_mount, &tracefs_mount_count);
+
+	return dentry;
+}
+
+struct dentry *eventfs_failed_creating(struct dentry *dentry)
+{
+	dput(dentry);
+	simple_release_fs(&tracefs_mount, &tracefs_mount_count);
+	return NULL;
+}
+
+struct dentry *eventfs_end_creating(struct dentry *dentry)
+{
+	return dentry;
+}
+
 /**
  * tracefs_create_file - create a file in the tracefs filesystem
  * @name: a pointer to a string containing the name of the file to create.
diff --git a/include/linux/tracefs.h b/include/linux/tracefs.h
index b02cbba..52201f3 100644
--- a/include/linux/tracefs.h
+++ b/include/linux/tracefs.h
@@ -38,6 +38,12 @@ struct eventfs_file {
 	bool                            created;
 };
 
+struct dentry *eventfs_start_creating(const char *name, struct dentry *parent);
+
+struct dentry *eventfs_failed_creating(struct dentry *dentry);
+
+struct dentry *eventfs_end_creating(struct dentry *dentry);
+
 struct dentry *eventfs_create_events_dir(const char *name,
 					 struct dentry *parent);
 
-- 
2.7.4