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From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org
Cc: Al Viro <viro@ZenIV.linux.org.uk>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Al Viro <viro@ZenIV.linux.org.uk>
Subject: [for-next][PATCH 5/7] tracing: Automatically mount tracefs on debugfs/tracing
Date: Wed, 04 Feb 2015 09:34:25 -0500	[thread overview]
Message-ID: <20150204143755.694479564@goodmis.org> (raw)
In-Reply-To: <20150204143420.290584004@goodmis.org>

[-- Attachment #1: 0005-tracing-Automatically-mount-tracefs-on-debugfs-traci.patch --]
[-- Type: text/plain, Size: 2682 bytes --]

From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

As tools currently rely on the tracing directory in debugfs, we can not
just created a tracefs infrastructure and expect sysadmins to mount
the new tracefs to have their old tools work.

Instead, the debugfs tracing directory is still created and the tracefs
file system is mounted there when the debugfs filesystem is mounted.

No longer does the tracing infrastructure update the debugfs file system,
but instead interacts with the tracefs file system. But now, it still
appears to the user like nothing changed, except you also have the feature
of mounting just the tracing system without needing all of debugfs!

Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/trace.c | 36 +++++++++++++++++++++++++++++++++---
 1 file changed, 33 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 6c4739bee4bb..b4aa936509d2 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -32,6 +32,7 @@
 #include <linux/splice.h>
 #include <linux/kdebug.h>
 #include <linux/string.h>
+#include <linux/mount.h>
 #include <linux/rwsem.h>
 #include <linux/slab.h>
 #include <linux/ctype.h>
@@ -6535,6 +6536,28 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
 
 }
 
+static struct vfsmount *trace_automount(void *ingore)
+{
+	struct vfsmount *mnt;
+	struct file_system_type *type;
+
+	/*
+	 * To maintain backward compatibility for tools that mount
+	 * debugfs to get to the tracing facility, tracefs is automatically
+	 * mounted to the debugfs/tracing directory.
+	 */
+	type = get_fs_type("tracefs");
+	if (!type)
+		return NULL;
+	mnt = vfs_kern_mount(type, 0, "tracefs", NULL);
+	put_filesystem(type);
+	if (IS_ERR(mnt))
+		return NULL;
+	mntget(mnt);
+
+	return mnt;
+}
+
 /**
  * tracing_init_dentry - initialize top level trace array
  *
@@ -6546,14 +6569,21 @@ struct dentry *tracing_init_dentry(void)
 {
 	struct trace_array *tr = &global_trace;
 
+	/* The top level trace array uses  NULL as parent */
 	if (tr->dir)
-		return tr->dir;
+		return NULL;
 
 	if (WARN_ON(!debugfs_initialized()))
 		return ERR_PTR(-ENODEV);
 
-	tr->dir = debugfs_create_dir("tracing", NULL);
-
+	/*
+	 * As there may still be users that expect the tracing
+	 * files to exist in debugfs/tracing, we must automount
+	 * the tracefs file system there, so older tools still
+	 * work with the newer kerenl.
+	 */
+	tr->dir = debugfs_create_automount("tracing", NULL,
+					   trace_automount, NULL);
 	if (!tr->dir) {
 		pr_warn_once("Could not create debugfs directory 'tracing'\n");
 		return ERR_PTR(-ENOMEM);
-- 
2.1.4



  parent reply	other threads:[~2015-02-04 14:38 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-02-04 14:34 [for-next][PATCH 0/7] tracing: Add new filesystem tracefs Steven Rostedt
2015-02-04 14:34 ` [for-next][PATCH 1/7] tracing: Only create tracer options files if directory exists Steven Rostedt
2015-02-04 14:34 ` [for-next][PATCH 2/7] tracing: Create cmdline tracer options on tracing fs init Steven Rostedt
2015-02-04 14:34 ` [for-next][PATCH 3/7] tracefs: Add new tracefs file system Steven Rostedt
2015-02-09  5:56   ` Namhyung Kim
2015-02-09 15:04     ` Steven Rostedt
2015-02-04 14:34 ` [for-next][PATCH 4/7] tracing: Convert the tracing facility over to use tracefs Steven Rostedt
2015-02-04 14:34 ` Steven Rostedt [this message]
2015-02-09  6:00   ` [for-next][PATCH 5/7] tracing: Automatically mount tracefs on debugfs/tracing Namhyung Kim
2015-02-09 15:06     ` Steven Rostedt
2015-02-04 14:34 ` [for-next][PATCH 6/7] tracefs: Add directory /sys/kernel/tracing Steven Rostedt
2015-02-04 14:34 ` [for-next][PATCH 7/7] tracing: Have mkdir and rmdir be part of tracefs Steven Rostedt
2015-02-09  6:07   ` Namhyung Kim
2015-02-09 15:07     ` Steven Rostedt

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