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From: Al Viro <viro@ZenIV.linux.org.uk>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 00/16 v3] tracing: Add new file system tracefs
Date: Mon, 26 Jan 2015 19:30:49 +0000	[thread overview]
Message-ID: <20150126193049.GN29656@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20150126150913.653681560@goodmis.org>

On Mon, Jan 26, 2015 at 10:09:13AM -0500, Steven Rostedt wrote:
> There has been complaints that tracing is tied too much to debugfs,
> as there are systems that would like to perform tracing, but do
> not mount debugfs for security reasons. That is because any subsystem
> may use debugfs for debugging, and these interfaces are not always
> tested for security.
> 
> Creating a new tracefs that the tracing directory will now be attached
> to allows system admins the ability to access the tracing directory
> without the need to mount debugfs.
> 
> Another advantage is that debugfs does not support the system calls
> for mkdir and rmdir. Tracing uses these system calls to create new
> instances for sub buffers. This was done by a hack that hijacked the
> dentry ops from the "instances" debugfs dentry, and replacing it with
> one that could work.
> 
> Instead of using this hack, tracefs can provide a proper interface to
> allow the tracing system to have a mkdir and rmdir feature.
> 
> To maintain backward compatibility with older tools that expect that
> the tracing directory is mounted with debugfs, the tracing directory
> is still created under debugfs and tracefs is automatically mounted
> there.
> 
> Finally, a new directory is created when tracefs is enabled called
> /sys/kernel/tracing. This will be the new location that system admins
> may mount tracefs if they are not using debugfs.

You are still fighting an inconvenient API, but now it's not debugfs one -
it's your copy thereof.  Why not give your instances/ an inode_operations
of its own?  One with ->mkdir() and ->rmdir(), leaving all other directories
as-is.  That way you don't need the secondary methods at all.  And sure,
debugfs_create_dir() grabs ->i_mutex on parent, making you drop that in
your ->mkdir() if you want to call it.  But now you are not talking to it -
just to your own code, where you are free to change the calling conventions,
making it caller's responsibility to get that ->i_mutex.  The same goes for
the rmdir side...

  parent reply	other threads:[~2015-01-26 19:30 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-26 15:09 Steven Rostedt
2015-01-26 15:09 ` [PATCH 01/16 v3] debugfs_{mkdir,create,link}(): get rid of redundant argument Steven Rostedt
2015-01-26 15:09 ` [PATCH 02/16 v3] debugfs: split the beginning and the end of __create_file() off Steven Rostedt
2015-01-26 15:09 ` [PATCH 03/16 v3] debugfs: kill __create_file() Steven Rostedt
2015-01-26 15:09 ` [PATCH 04/16 v3] fold debugfs_link() into caller Steven Rostedt
2015-01-26 15:09 ` [PATCH 05/16 v3] debugfs_mknod(): get rid useless arguments Steven Rostedt
2015-01-26 15:09 ` [PATCH 06/16 v3] fold debugfs_mkdir() into caller Steven Rostedt
2015-01-26 15:09 ` [PATCH 07/16 v3] fold debugfs_create() " Steven Rostedt
2015-01-26 15:09 ` [PATCH 08/16 v3] fold debugfs_mknod() into callers Steven Rostedt
2015-01-26 15:09 ` [PATCH 09/16 v3] debugfs: take mode-dependent parts of debugfs_get_inode() " Steven Rostedt
2015-01-26 15:09 ` [PATCH 10/16 v3] debugfs: split end_creating() into success and failure cases Steven Rostedt
2015-01-26 15:09 ` [PATCH 11/16 v3] new primitive: debugfs_create_automount() Steven Rostedt
2015-01-26 15:09 ` [PATCH 12/16 v3] tracefs: Add new tracefs file system Steven Rostedt
2015-01-26 15:09 ` [PATCH 13/16 v3] tracing: Convert the tracing facility over to use tracefs Steven Rostedt
2015-01-26 15:09 ` [PATCH 14/16 v3] tracing: Automatically mount tracefs on debugfs/tracing Steven Rostedt
2015-01-26 15:09 ` [PATCH 15/16 v3] tracefs: Add directory /sys/kernel/tracing Steven Rostedt
2015-01-26 15:09 ` [PATCH 16/16 v3] tracing: Have mkdir and rmdir be part of tracefs Steven Rostedt
2015-01-26 19:30 ` Al Viro [this message]
2015-01-26 20:42   ` [PATCH 00/16 v3] tracing: Add new file system tracefs Steven Rostedt
2015-01-26 20:44     ` Steven Rostedt
2015-01-26 20:58       ` Steven Rostedt
2015-01-26 21:44         ` Al Viro
2015-01-26 21:46     ` Al Viro
2015-01-26 23:02       ` Al Viro
2015-01-26 23:39         ` Steven Rostedt
2015-01-26 23:43       ` Steven Rostedt
2015-01-26 23:49         ` Steven Rostedt
2015-01-27  0:39           ` Steven Rostedt
2015-01-27  4:34             ` Al Viro
2015-01-27 15:15               ` Steven Rostedt
2015-01-27  0:37         ` Al Viro
2015-01-27  1:02           ` Steven Rostedt
2015-01-27  1:03             ` Steven Rostedt
2015-01-27  4:38               ` Al Viro
2015-01-27 15:19                 ` Steven Rostedt
2015-01-27 15:44                   ` Steven Rostedt
2015-01-26 21:40   ` Al Viro
2015-01-26 23:37     ` Steven Rostedt
2015-01-27  2:34       ` Steven Rostedt
2015-01-27  4:46         ` Al Viro

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