[PATCH v5 07/10] eventfs: Implement functions to create files and dirs when accessed

[Ajay Kaher]

Add create_file() and create_dir() functions to create the files and
directories respectively when they are accessed. The functions will be
called from the lookup operation of the inode_operations or from the open
function of file_operations.

Signed-off-by: Ajay Kaher <akaher@xxxxxxxxxx>
Co-developed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Tested-by: Ching-lin Yu <chinglinyu@xxxxxxxxxx>
---
 fs/tracefs/event_inode.c | 55 +++++++++++++++++++++++++++--
 fs/tracefs/inode.c       | 74 ++++++++++++++++++++++++++++++++++++++++
 include/linux/tracefs.h  |  7 ++++
 3 files changed, 134 insertions(+), 2 deletions(-)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index a3c1b8bf7192..af70d6ffb923 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -101,7 +101,34 @@ static struct dentry *create_file(const char *name, umode_t mode,
 				  struct dentry *parent, void *data,
 				  const struct file_operations *fop)
 {
-	return NULL;
+	struct tracefs_inode *ti;
+	struct dentry *dentry;
+	struct inode *inode;
+
+	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;
+	d_instantiate(dentry, inode);
+	fsnotify_create(dentry->d_parent->d_inode, dentry);
+	return eventfs_end_creating(dentry);
 };
 
 /**
@@ -123,7 +150,31 @@ static struct dentry *create_file(const char *name, umode_t mode,
  */
 static struct dentry *create_dir(const char *name, struct dentry *parent, void *data)
 {
-	return NULL;
+	struct tracefs_inode *ti;
+	struct dentry *dentry;
+	struct inode *inode;
+
+	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 = 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 = data;
+
+	ti = get_tracefs(inode);
+	ti->flags |= TRACEFS_EVENT_INODE;
+
+	inc_nlink(inode);
+	d_instantiate(dentry, inode);
+	inc_nlink(dentry->d_parent->d_inode);
+	fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
+	return eventfs_end_creating(dentry);
 }
 
 /**
diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index 4acc4b4dfd22..d9273066f25f 100644
--- a/fs/tracefs/inode.c
+++ b/fs/tracefs/inode.c
@@ -474,6 +474,80 @@ struct dentry *tracefs_end_creating(struct dentry *dentry)
 	return dentry;
 }
 
+/**
+ * eventfs_start_creating - start the process of creating a dentry
+ * @name: Name of the file created for the dentry
+ * @parent: The parent dentry where this dentry will be created
+ *
+ * This is a simple helper function for the dynamically created eventfs
+ * files. When the directory of the eventfs files are accessed, their
+ * dentries are created on the fly. This function is used to start that
+ * process.
+ */
+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;
+}
+
+/**
+ * eventfs_failed_creating - clean up a failed eventfs dentry creation
+ * @dentry: The dentry to clean up
+ *
+ * If after calling eventfs_start_creating(), a failure is detected, the
+ * resources created by eventfs_start_creating() needs to be cleaned up. In
+ * that case, this function should be called to perform that clean up.
+ */
+struct dentry *eventfs_failed_creating(struct dentry *dentry)
+{
+	dput(dentry);
+	simple_release_fs(&tracefs_mount, &tracefs_mount_count);
+	return NULL;
+}
+
+/**
+ * eventfs_end_creating - Finish the process of creating a eventfs dentry
+ * @dentry: The dentry that has successfully been created.
+ *
+ * This function is currently just a place holder to match
+ * eventfs_start_creating(). In case any synchronization needs to be added,
+ * this function will be used to implement that without having to modify
+ * the callers of eventfs_start_creating().
+ */
+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 54c9cbd0389b..cdb21d63a127 100644
--- a/include/linux/tracefs.h
+++ b/include/linux/tracefs.h
@@ -23,6 +23,13 @@ struct file_operations;
 
 struct eventfs_file;
 
+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);
 
-- 
2.39.0