From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759323AbbBIF6F (ORCPT ); Mon, 9 Feb 2015 00:58:05 -0500 Received: from lgeamrelo04.lge.com ([156.147.1.127]:65239 "EHLO lgeamrelo04.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753003AbbBIF6D (ORCPT ); Mon, 9 Feb 2015 00:58:03 -0500 X-Original-SENDERIP: 10.177.220.203 X-Original-MAILFROM: namhyung@kernel.org Date: Mon, 9 Feb 2015 14:56:19 +0900 From: Namhyung Kim To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Al Viro , Greg Kroah-Hartman , Ingo Molnar , Andrew Morton Subject: Re: [for-next][PATCH 3/7] tracefs: Add new tracefs file system Message-ID: <20150209055619.GA30788@sejong> References: <20150204143420.290584004@goodmis.org> <20150204143755.373406887@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20150204143755.373406887@goodmis.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Steve, On Wed, Feb 04, 2015 at 09:34:23AM -0500, Steven Rostedt wrote: > From: "Steven Rostedt (Red Hat)" > > Add a separate file system to handle the tracing directory. Currently it > is part of debugfs, but that is starting to show its limits. > > One thing is that in order to access the tracing infrastructure, you need > to mount debugfs. As that includes debugging from all sorts of sub systems > in the kernel, it is not considered advisable to mount such an all > encompassing debugging system. > > Having the tracing system in its own file systems gives access to the > tracing sub system without needing to include all other systems. > > Another problem with tracing using the debugfs system is that the > instances use mkdir to create sub buffers. debugfs does not support mkdir > from userspace so to implement it, special hacks were used. By controlling > the file system that the tracing infrastructure uses, this can be properly > done without hacks. > > Signed-off-by: Steven Rostedt > --- [SNIP] > +/** > + * tracefs_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, or a directory (if you want > + * to create a directory, the tracefs_create_dir() function is > + * recommended to be used instead.) > + * > + * 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. I cannot find where it returns -ENODEV. AFAICS we cannot call tracefs functions if tracing was not enabled. > + */ > +struct dentry *tracefs_create_file(const char *name, umode_t mode, > + struct dentry *parent, void *data, > + const struct file_operations *fops) > +{ > + struct dentry *dentry; > + struct inode *inode; > + > + if (!(mode & S_IFMT)) > + mode |= S_IFREG; > + BUG_ON(!S_ISREG(mode)); > + dentry = start_creating(name, parent); > + > + if (IS_ERR(dentry)) > + return NULL; > + > + inode = tracefs_get_inode(dentry->d_sb); > + if (unlikely(!inode)) > + return failed_creating(dentry); > + > + inode->i_mode = mode; > + inode->i_fop = fops ? fops : &tracefs_file_operations; > + inode->i_private = data; > + d_instantiate(dentry, inode); > + fsnotify_create(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 > + * 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. > + * > + * This function creates a directory in tracefs with the given name. > + * > + * 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. If an error occurs, %NULL will be returned. > + * > + * If tracing is not enabled in the kernel, the value -%ENODEV will be > + * returned. Ditto. Thanks, Namhyung > + */ > +struct dentry *tracefs_create_dir(const char *name, struct dentry *parent) > +{ > + 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 = &simple_dir_inode_operations; > + 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); > +}