Some more nits.

Subject: eventfs: Implement functions to create files and dirs when accessed

On Thu, 13 Jul 2023 17:03:20 +0530
Ajay Kaher [off-list ref] wrote:

Adding create_file(), create_dir() to create file, dir
at runtime when they are accessed.

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

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.

Again, should move the extra lines into the description.

+ * @fop: 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 *create_file(const char *name, umode_t mode,
+				  struct dentry *parent, void *data,
+				  const struct file_operations *fop)
+{
+	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);
+}
+
+/**
+ * create_dir - create a dir in the tracefs filesystem
+ * @name: the name of the file to create.
+ * @mode: the permission that the file should have.
+ * @parent: parent dentry for this file.
+ * @data: 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.

Move the extra lines down into the description here too.

This needs to be documented. What about:

/**
 * 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;
+}

-- Steve