[RFC Patch 0/1] Enhancements to 'trace' infrastructure

[RFC Patch 0/1] Enhancements to 'trace' infrastructure

[K. Prasad]

Hi All,
	Please review the following patch which introduces two new
interfaces to output data using 'trace' infrastructure. These interfaces
can be used to print directly onto a debugfs mount. Since it uses 'trace'
interface underneath the directory and file structures are as created by
'trace'.

The proposed debugfs_* interfaces are meant to overcome the need to
setup/tear-down 'trace' infrastructure by the user. In addition to this
the patches help in:

a) Printing out data into a debugfs mounted file without bothering about
creating/re-using debugfs files, sizes of intermediate buffers, etc.
(This is achieved through the functions init_trace_interface() and
trace_exists()).
b) Provide interfaces to do i)string output or ii)binary dump of data
c) Tear-down of the trace infrastructure through a single function call
using its parent directory name, and unmindful of the internal data
structures such as 'struct trace_info'.(using trace_cleanup_all)
d) The debugfs_printk_data may be further enhanced to provide features
suh as the ability to invoke pre- and post- printing callback functions
For e.g. A callback function to obtain a given lock before printing out
a given data, etc.
 
A quick look at samples/trace/fork_trace.c would help understand what is
required to get data out using the 'trace' infrastructure (vs the
proposed interfaces which have been exemplified in
samples/trace/fork_new_trace.c).

The patches are based against 2.6.25-rc8-mm1 and have been tested on an
i386 machine.

Thanks,
K.Prasad

[RFC Patch 1/1] debugfs_printk and debugfs_dump interface

[K. Prasad]

This patch introduces two new interfaces called debugfs_printk and 
debugfs_dump which can be used to print to the debugfs mount directly.
It uses the 'trace' infrastructure underneath and is a patch over it.
A sample file is also created to demonstrate its ease of use.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 include/linux/trace.h          |   54 ++++++++++++
 lib/trace.c                    |  183 +++++++++++++++++++++++++++++++++++++++--
 samples/trace/Makefile         |    2 
 samples/trace/fork_new_trace.c |   98 +++++++++++++++++++++
 4 files changed, 331 insertions(+), 6 deletions(-)

Index: linux-2.6.25-rc8-mm1/include/linux/trace.h
===================================================================
--- linux-2.6.25-rc8-mm1.orig/include/linux/trace.h
+++ linux-2.6.25-rc8-mm1/include/linux/trace.h
@@ -39,10 +39,30 @@ enum trace_state {
 	TRACE_STOPPED,
 };
 
+enum trace_dir_state {
+	TRACE_PARENT_DIR_ABSENT,
+	TRACE_PARENT_DIR_EXISTS,
+	TRACE_DIR_EXISTS
+};
+
 #define TRACE_ROOT_NAME_SIZE	64	/* Max root dir identifier */
 #define TRACE_NAME_SIZE		64	/* Max trace identifier */
 
 /*
+ * Buffers for use by debugfs_printk
+ */
+#define DEFAULT_TRACE_BUF_SIZE 4096
+#define DEFAULT_TRACE_SUB_BUF_NR 40
+
+struct debugfs_printk_data {
+	char *parent_dir;
+	char *dir;
+	int exists;
+	int buf_size;
+	int sub_buf_size;
+};
+
+/*
  * Global root user information
  */
 struct trace_root {
@@ -73,6 +93,17 @@ struct trace_info {
 	unsigned int buf_nr;
 };
 
+/*
+ * Information about every trace directory
+ */
+struct trace_dir {
+	struct list_head trace_dir_list;
+	char trace_dir_name[TRACE_NAME_SIZE];
+	struct dentry *trace_root;
+	struct dentry *trace_dir;
+	struct trace_info *ti;
+};
+
 #ifdef CONFIG_TRACE
 static inline int trace_running(struct trace_info *trace)
 {
@@ -83,6 +114,12 @@ struct trace_info *trace_setup(const cha
 int trace_start(struct trace_info *trace);
 int trace_stop(struct trace_info *trace);
 void trace_cleanup(struct trace_info *trace);
+int trace_exists(const char *parent_dir, const char *dir,
+					struct trace_info **ti);
+void trace_cleanup_all(const char *parent_dir);
+int debugfs_printk(struct debugfs_printk_data *dpk, char *format, ...);
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len);
 #else
 static inline struct trace_info *trace_setup(const char *root,
 					     const char *name, u32 buf_size,
@@ -94,6 +131,23 @@ static inline int trace_start(struct tra
 static inline int trace_stop(struct trace_info *trace) { return -EINVAL; }
 static inline int trace_running(struct trace_info *trace) { return 0; }
 static inline void trace_cleanup(struct trace_info *trace) {}
+static inline int trace_exists(const char *parent_dir, const char *dir,
+				struct trace_info **ti)
+{
+	return -EINVAL;
+}
+static inline void trace_cleanup_all(const char *parent_dir) {}
+static inline int debugfs_printk(struct debugfs_printk_data *dpk, char *format,
+				...)
+{
+	return -EINVAL;
+}
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len)
+{
+	return -EINVAL;
+}
+
 #endif
 
 #endif
Index: linux-2.6.25-rc8-mm1/lib/trace.c
===================================================================
--- linux-2.6.25-rc8-mm1.orig/lib/trace.c
+++ linux-2.6.25-rc8-mm1/lib/trace.c
@@ -29,6 +29,7 @@
 #include <linux/trace.h>
 
 static LIST_HEAD(trace_roots);
+static LIST_HEAD(trace_dirs);
 static DEFINE_MUTEX(trace_mutex);
 
 static int state_open(struct inode *inode, struct file *filp)
@@ -99,9 +100,19 @@ static void remove_root(struct trace_inf
 
 static void remove_tree(struct trace_info *trace)
 {
+	struct list_head *pos, *temp;
+	struct trace_dir *dr = NULL;
+
 	mutex_lock(&trace_mutex);
 	debugfs_remove(trace->dir);
 
+	list_for_each_safe(pos, temp, &trace_dirs) {
+		dr = list_entry(pos, struct trace_dir, trace_dir_list);
+		if (dr->ti == trace) {
+			list_del(pos);
+			kfree(dr);
+		}
+	}
 	if (trace->root) {
 		if (--trace->root->users == 0)
 			remove_root(trace);
@@ -142,11 +153,16 @@ static struct trace_root *lookup_root(co
 static struct dentry *create_tree(struct trace_info *trace, const char *root,
 				  const char *name)
 {
-	struct dentry *dir = NULL;
+	struct trace_dir *temp;
 
 	if (root == NULL || name == NULL)
 		return ERR_PTR(-EINVAL);
 
+	temp = kzalloc(sizeof(struct trace_dir), GFP_KERNEL);
+	if (!temp)
+		return ERR_PTR(-ENOMEM);
+	strncpy(temp->trace_dir_name, name, strlen(name));
+
 	mutex_lock(&trace_mutex);
 
 	trace->root = lookup_root(root);
@@ -155,16 +171,49 @@ static struct dentry *create_tree(struct
 		goto err;
 	}
 
-	dir = debugfs_create_dir(name, trace->root->root);
-	if (IS_ERR(dir))
+	temp->trace_root = trace->root->root;
+	temp->trace_dir = debugfs_create_dir(name, trace->root->root);
+
+	if (IS_ERR(temp->trace_dir))
 		remove_root(trace);
-	else
+	else {
 		trace->root->users++;
+		temp->ti = trace;
+		list_add_tail(&temp->trace_dir_list, &trace_dirs);
+	}
 
 err:
 	mutex_unlock(&trace_mutex);
-	return dir;
+	return temp->trace_dir;
+}
+
+int trace_exists(const char *parent_dir, const char *dir,
+					struct trace_info **ti)
+{
+	struct list_head *pos;
+	struct trace_root *r;
+	struct trace_dir *temp;
+	int ret = TRACE_PARENT_DIR_ABSENT;
+
+	list_for_each(pos, &trace_roots) {
+		r = list_entry(pos, struct trace_root, list);
+		if (!strcmp(parent_dir, r->name))
+			goto search_dir;
+	}
+	return ret;
+
+ search_dir:
+	list_for_each(pos, &trace_dirs) {
+		temp = list_entry(pos, struct trace_dir, trace_dir_list);
+
+		if (!strcmp(dir, temp->trace_dir_name)) {
+			*ti = temp->ti;
+			return TRACE_DIR_EXISTS;
+		}
+	}
+	return TRACE_PARENT_DIR_EXISTS;
 }
+EXPORT_SYMBOL_GPL(trace_exists);
 
 static int dropped_open(struct inode *inode, struct file *filp)
 {
@@ -561,3 +610,127 @@ void trace_cleanup(struct trace_info *tr
 	kfree(trace);
 }
 EXPORT_SYMBOL_GPL(trace_cleanup);
+
+/**
+ *	trace_cleanup_all - Removes all trace_info/directories created under a
+ *			    parent_dir
+ *	@parent_dir: Name of the parent directory
+ */
+void trace_cleanup_all(const char *parent_dir)
+{
+	struct list_head *pos, *pos_temp;
+	struct trace_dir *temp;
+
+	list_for_each_safe(pos, pos_temp, &trace_dirs) {
+		temp = list_entry(pos, struct trace_dir, trace_dir_list);
+		if (!strcmp(parent_dir, temp->trace_root->d_iname))
+			trace_cleanup(temp->ti);
+	}
+}
+EXPORT_SYMBOL_GPL(trace_cleanup_all);
+
+/*
+ * Send formatted trace data to trace channel.
+ */
+static int trace_printf_(struct trace_info *trace, const char *format,
+								va_list ap)
+{
+	va_list aq;
+	char *record;
+	int len;
+	int ret = 0;
+
+	if (trace_running(trace)) {
+		va_copy(aq, ap);
+		len = vsnprintf(NULL, 0, format, aq);
+		va_end(aq);
+		record = relay_reserve(trace->rchan, ++len);
+		if (record)
+			ret = vsnprintf(record, len, format, ap);
+	}
+	return ret;
+}
+
+static inline struct trace_info *init_trace_interface(struct
+						debugfs_printk_data * dpk)
+{
+	struct trace_info *ti;
+
+	dpk->exists = trace_exists(dpk->parent_dir, dpk->dir, &ti);
+
+	switch (dpk->exists) {
+
+	case TRACE_PARENT_DIR_EXISTS:
+	case TRACE_PARENT_DIR_ABSENT:
+		if (!dpk->buf_size)
+			dpk->buf_size = DEFAULT_TRACE_BUF_SIZE;
+		if (!dpk->sub_buf_size)
+			dpk->sub_buf_size = DEFAULT_TRACE_SUB_BUF_NR;
+		ti = trace_setup(dpk->parent_dir, dpk->dir,
+			dpk->buf_size, dpk->sub_buf_size, TRACE_FLIGHT_CHANNEL);
+		printk(KERN_INFO "Trace interface %s setup\n",
+							ti->dir->d_iname);
+		if (IS_ERR(ti)) {
+			printk(KERN_ERR "Trace interface could not be "
+							"initialised\n");
+			return PTR_ERR(ti);
+		}
+		/* Fall through */
+	case TRACE_DIR_EXISTS:
+		if (ti->state != TRACE_RUNNING)
+			trace_start(ti);
+	}
+	return ti;
+}
+
+/*
+ * debugfs_printk - A function to write into the debugfs mount 'directly'
+ * using 'trace' infrastructure
+ * @dpk - Structure containing info such as parent_dir and directory
+ * @format - String containing format string specifiers
+ */
+int debugfs_printk(struct debugfs_printk_data *dpk, char *format, ...)
+{
+	int ret;
+	struct trace_info *ti;
+	va_list(ap);
+
+	va_start(ap, format);
+
+	ti = init_trace_interface(dpk);
+
+	/* Now do the actual printing */
+	rcu_read_lock();
+	ret = trace_printf_(ti, format, ap);
+	rcu_read_unlock();
+
+	va_end(ap);
+	return ret;
+}
+EXPORT_SYMBOL(debugfs_printk);
+
+/*
+ * @output - Data that needs to be output
+ * @output_len - Length of the output data
+ */
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len)
+{
+	struct trace_info *ti;
+	char *record;
+	int ret = 0;
+
+	ti = init_trace_interface(dpk);
+
+	/* Now do the actual printing */
+	rcu_read_lock();
+	record = relay_reserve(ti->rchan, output_len);
+	if (record)
+		memcpy(record, output, output_len);
+	else
+		ret = -ENOMEM;
+	rcu_read_unlock();
+
+	return ret;
+}
+EXPORT_SYMBOL(debugfs_dump);
Index: linux-2.6.25-rc8-mm1/samples/trace/fork_new_trace.c
===================================================================
--- /dev/null
+++ linux-2.6.25-rc8-mm1/samples/trace/fork_new_trace.c
@@ -0,0 +1,98 @@
+/*
+ * An example of using trace in a kprobes module
+ *
+ * Copyright (C) 2008 IBM Inc.
+ *
+ * K.Prasad <prasad@linux.vnet.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * -------
+ * This module creates a trace channel and places a kprobe
+ * on the function do_fork(). The value of current->pid is written to
+ * the trace channel each time the kprobe is hit..
+ *
+ * How to run the example:
+ * $ mount -t debugfs /debug
+ * $ insmod fork_new_trace.ko
+ *
+ * To view the data produced by the module:
+ * $ cat /debug/trace_new_example/do_fork/trace0
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/kprobes.h>
+#include <linux/trace.h>
+
+#define SAMPLE_PARENT_DIR "trace_new_example"
+#define PROBE_POINT "do_fork"
+
+static struct kprobe kp;
+static struct debugfs_printk_data *dpk;
+
+static int handler_pre(struct kprobe *p, struct pt_regs *regs)
+{
+	debugfs_printk(dpk, "%d\n", current->pid);
+	return 0;
+}
+
+int init_module(void)
+{
+	int ret = 0;
+	int len_parent_dir, len_dir;
+
+	/* setup the kprobe */
+	kp.pre_handler = handler_pre;
+	kp.post_handler = NULL;
+	kp.fault_handler = NULL;
+	kp.symbol_name = PROBE_POINT;
+	ret = register_kprobe(&kp);
+	if (ret) {
+		printk(KERN_ERR "fork_trace: register_kprobe failed\n");
+		return ret;
+	}
+
+	len_parent_dir = strlen(SAMPLE_PARENT_DIR) + 1;
+	/* Initialising len_dir to the larger of the two dir names */
+	len_dir = strlen("kprobe_struct") + 1;
+
+	dpk = kzalloc(sizeof(*dpk), GFP_KERNEL);
+	if (!dpk)
+		ret = 1;
+
+	dpk->parent_dir = SAMPLE_PARENT_DIR;
+
+	/* Let's do a binary dump of struct kprobe using debugfs_dump */
+	dpk->dir = "kprobes_struct";
+	debugfs_dump(dpk, &kp, sizeof(kp));
+
+	/* Now change the directory to collect fork pid data */
+	dpk->dir = PROBE_POINT;
+
+	if (ret)
+		printk(KERN_ERR "Unable to find required free memory. "
+				"Trace new sample module loading aborted");
+	return ret;
+}
+
+void cleanup_module(void)
+{
+	unregister_kprobe(&kp);
+
+	/* Just a single cleanup call passing the parent dir string */
+	trace_cleanup_all(SAMPLE_PARENT_DIR);
+}
+MODULE_LICENSE("GPL");
Index: linux-2.6.25-rc8-mm1/samples/trace/Makefile
===================================================================
--- linux-2.6.25-rc8-mm1.orig/samples/trace/Makefile
+++ linux-2.6.25-rc8-mm1/samples/trace/Makefile
@@ -1,4 +1,4 @@
 # builds the trace example kernel modules;
 # then to use (as root):  insmod <fork_trace.ko>
 
-obj-$(CONFIG_SAMPLE_TRACE) := fork_trace.o
+obj-$(CONFIG_SAMPLE_TRACE) := fork_trace.o fork_new_trace.o

Re: [RFC Patch 1/1] debugfs_printk and debugfs_dump interface

[David Wilder]

K. Prasad wrote:
>

> +
> +struct debugfs_printk_data {
> +	char *parent_dir;
> +	char *dir;
> +	int exists;
> +	int buf_size;
> +	int sub_buf_size;
> +};

How about adding a "flags" field here to hold the trace channel flags. 
Pass the flags through to trace_setup().  This way the caller can 
control the trace options.

Add a description of debugfs_printk() and debugfs_dump() to 
Documentation/trace.txt.

Re: [RFC Patch 1/1] debugfs_printk and debugfs_dump interface

[K. Prasad]

On Wed, Apr 16, 2008 at 02:25:18PM -0700, David Wilder wrote:
> K. Prasad wrote:
> >
> 
> >+
> >+struct debugfs_printk_data {
> >+	char *parent_dir;
> >+	char *dir;
> >+	int exists;
> >+	int buf_size;
> >+	int sub_buf_size;
> >+};
> 
> How about adding a "flags" field here to hold the trace channel flags. 
> Pass the flags through to trace_setup().  This way the caller can 
> control the trace options.
> 
> Add a description of debugfs_printk() and debugfs_dump() to 
> Documentation/trace.txt.
Hi David,
	Thanks for your comments. I have added a flags field to struct
debugfs_printk_data (defaulting to TRACE_FLIGHT_CHANNEL) and updated the
documentation apart from a minor name change (trace_printf). Please
review the changes.

Thanks,
K.Prasad

This patch introduces two new interfaces called debugfs_printk and 
debugfs_dump which can be used to print to the debugfs mount directly.
It uses the 'trace' infrastructure underneath and is a patch over it.
A sample file is also created to demonstrate its ease of use.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 Documentation/trace.txt        |   21 ++++
 include/linux/trace.h          |   55 +++++++++++
 lib/trace.c                    |  196 +++++++++++++++++++++++++++++++++++++++--
 samples/trace/Makefile         |    2 
 samples/trace/fork_new_trace.c |   97 ++++++++++++++++++++
 5 files changed, 365 insertions(+), 6 deletions(-)

Index: linux-2.6.25-rc8-mm1/include/linux/trace.h
===================================================================
--- linux-2.6.25-rc8-mm1.orig/include/linux/trace.h
+++ linux-2.6.25-rc8-mm1/include/linux/trace.h
@@ -39,10 +39,31 @@ enum trace_state {
 	TRACE_STOPPED,
 };
 
+enum trace_dir_state {
+	TRACE_PARENT_DIR_ABSENT,
+	TRACE_PARENT_DIR_EXISTS,
+	TRACE_DIR_EXISTS
+};
+
 #define TRACE_ROOT_NAME_SIZE	64	/* Max root dir identifier */
 #define TRACE_NAME_SIZE		64	/* Max trace identifier */
 
 /*
+ * Buffers for use by debugfs_printk
+ */
+#define DEFAULT_TRACE_BUF_SIZE 4096
+#define DEFAULT_TRACE_SUB_BUF_NR 40
+
+struct debugfs_printk_data {
+	char *parent_dir;
+	char *dir;
+	int exists;
+	int buf_size;
+	int sub_buf_size;
+	unsigned long flags;
+};
+
+/*
  * Global root user information
  */
 struct trace_root {
@@ -73,6 +94,17 @@ struct trace_info {
 	unsigned int buf_nr;
 };
 
+/*
+ * Information about every trace directory
+ */
+struct trace_dir {
+	struct list_head trace_dir_list;
+	char trace_dir_name[TRACE_NAME_SIZE];
+	struct dentry *trace_root;
+	struct dentry *trace_dir;
+	struct trace_info *ti;
+};
+
 #ifdef CONFIG_TRACE
 static inline int trace_running(struct trace_info *trace)
 {
@@ -83,6 +115,12 @@ struct trace_info *trace_setup(const cha
 int trace_start(struct trace_info *trace);
 int trace_stop(struct trace_info *trace);
 void trace_cleanup(struct trace_info *trace);
+int trace_exists(const char *parent_dir, const char *dir,
+					struct trace_info **ti);
+void trace_cleanup_all(const char *parent_dir);
+int debugfs_printk(struct debugfs_printk_data *dpk, char *format, ...);
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len);
 #else
 static inline struct trace_info *trace_setup(const char *root,
 					     const char *name, u32 buf_size,
@@ -94,6 +132,23 @@ static inline int trace_start(struct tra
 static inline int trace_stop(struct trace_info *trace) { return -EINVAL; }
 static inline int trace_running(struct trace_info *trace) { return 0; }
 static inline void trace_cleanup(struct trace_info *trace) {}
+static inline int trace_exists(const char *parent_dir, const char *dir,
+				struct trace_info **ti)
+{
+	return -EINVAL;
+}
+static inline void trace_cleanup_all(const char *parent_dir) {}
+static inline int debugfs_printk(struct debugfs_printk_data *dpk, char *format,
+				...)
+{
+	return -EINVAL;
+}
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len)
+{
+	return -EINVAL;
+}
+
 #endif
 
 #endif
Index: linux-2.6.25-rc8-mm1/lib/trace.c
===================================================================
--- linux-2.6.25-rc8-mm1.orig/lib/trace.c
+++ linux-2.6.25-rc8-mm1/lib/trace.c
@@ -29,7 +29,9 @@
 #include <linux/trace.h>
 
 static LIST_HEAD(trace_roots);
+static LIST_HEAD(trace_dirs);
 static DEFINE_MUTEX(trace_mutex);
+static DEFINE_SPINLOCK(trace_lock);
 
 static int state_open(struct inode *inode, struct file *filp)
 {
@@ -99,9 +101,19 @@ static void remove_root(struct trace_inf
 
 static void remove_tree(struct trace_info *trace)
 {
+	struct list_head *pos, *temp;
+	struct trace_dir *dr = NULL;
+
 	mutex_lock(&trace_mutex);
 	debugfs_remove(trace->dir);
 
+	list_for_each_safe(pos, temp, &trace_dirs) {
+		dr = list_entry(pos, struct trace_dir, trace_dir_list);
+		if (dr->ti == trace) {
+			list_del(pos);
+ 			kfree(dr);
+		}
+	}
 	if (trace->root) {
 		if (--trace->root->users == 0)
 			remove_root(trace);
@@ -142,11 +154,14 @@ static struct trace_root *lookup_root(co
 static struct dentry *create_tree(struct trace_info *trace, const char *root,
 				  const char *name)
 {
-	struct dentry *dir = NULL;
+	struct trace_dir *temp;
 
 	if (root == NULL || name == NULL)
 		return ERR_PTR(-EINVAL);
 
+	temp = kzalloc(sizeof(struct trace_dir), GFP_KERNEL);
+	strncpy(temp->trace_dir_name, name, strlen(name));
+
 	mutex_lock(&trace_mutex);
 
 	trace->root = lookup_root(root);
@@ -155,16 +170,49 @@ static struct dentry *create_tree(struct
 		goto err;
 	}
 
-	dir = debugfs_create_dir(name, trace->root->root);
-	if (IS_ERR(dir))
+	temp->trace_root = trace->root->root;
+	temp->trace_dir = debugfs_create_dir(name, trace->root->root);
+
+	if (IS_ERR(temp->trace_dir))
 		remove_root(trace);
-	else
+	else {
 		trace->root->users++;
+		temp->ti = trace;
+		list_add_tail(&temp->trace_dir_list, &trace_dirs);
+	}
 
 err:
 	mutex_unlock(&trace_mutex);
-	return dir;
+	return temp->trace_dir;
+}
+
+int trace_exists(const char *parent_dir, const char *dir,
+					struct trace_info **ti)
+{
+	struct list_head *pos;
+	struct trace_root *r;
+	struct trace_dir *temp;
+	int ret = TRACE_PARENT_DIR_ABSENT;
+
+	list_for_each(pos, &trace_roots) {
+		r = list_entry(pos, struct trace_root, list);
+		if (!strcmp(parent_dir, r->name))
+			goto search_dir;
+	}
+	return ret;
+
+ search_dir:
+	list_for_each(pos, &trace_dirs) {
+		temp = list_entry(pos, struct trace_dir, trace_dir_list);
+
+		if (!strcmp(dir, temp->trace_dir_name)) {
+			*ti = temp->ti;
+			return TRACE_DIR_EXISTS;
+		}
+	}
+	return TRACE_PARENT_DIR_EXISTS;
 }
+EXPORT_SYMBOL_GPL(trace_exists);
 
 static int dropped_open(struct inode *inode, struct file *filp)
 {
@@ -561,3 +609,141 @@ void trace_cleanup(struct trace_info *tr
 	kfree(trace);
 }
 EXPORT_SYMBOL_GPL(trace_cleanup);
+
+/**
+ *	trace_cleanup_all - Removes all trace_info/directories created under a
+ *			    parent_dir
+ *	@parent_dir: Name of the parent directory
+ */
+void trace_cleanup_all(const char *parent_dir)
+{
+	struct list_head *pos, *pos_temp;
+	struct trace_dir *temp;
+
+	list_for_each_safe(pos, pos_temp, &trace_dirs) {
+		temp = list_entry(pos, struct trace_dir, trace_dir_list);
+		if (!strcmp(parent_dir, temp->trace_root->d_iname))
+			trace_cleanup(temp->ti);
+	}
+}
+EXPORT_SYMBOL_GPL(trace_cleanup_all);
+
+/*
+ * Send formatted trace data to trace channel.
+ */
+static int trace_printf(struct trace_info *trace, const char *format,
+								va_list ap)
+{
+	va_list aq;
+	char *record;
+	int len;
+	int ret = 0;
+
+	if (trace_running(trace)) {
+		va_copy(aq, ap);
+		len = vsnprintf(NULL, 0, format, aq);
+		va_end(aq);
+		record = relay_reserve(trace->rchan, ++len);
+		if (record)
+			ret = vsnprintf(record, len, format, ap);
+	}
+	return ret;
+}
+
+static inline struct trace_info *init_trace_interface(struct
+                        			debugfs_printk_data *dpk)
+{
+        struct trace_info *ti;
+
+        dpk->exists = trace_exists(dpk->parent_dir, dpk->dir, &ti);
+
+        switch(dpk->exists) {
+
+        case TRACE_PARENT_DIR_EXISTS:
+        case TRACE_PARENT_DIR_ABSENT:
+                if(!dpk->buf_size)
+                        dpk->buf_size = DEFAULT_TRACE_BUF_SIZE;
+                if(!dpk->sub_buf_size)
+                        dpk->sub_buf_size = DEFAULT_TRACE_SUB_BUF_NR;
+                if(!dpk->flags)
+			dpk->flags = TRACE_FLIGHT_CHANNEL;
+                ti = trace_setup(dpk->parent_dir, dpk->dir,
+                        dpk->buf_size, dpk->sub_buf_size, dpk->flags);
+                printk(KERN_INFO "Trace interface %s setup through "
+                                                        "debugfs_printk\n",
+                                                        ti->dir->d_iname);
+                if (IS_ERR(ti)) {
+                        printk(KERN_ERR "Trace interface could not be "
+                        "initialised\n");
+                        return PTR_ERR(ti);
+                }
+                /* Fall through */
+        case TRACE_DIR_EXISTS:
+                if (ti->state != TRACE_RUNNING) {
+                        trace_start(ti);
+                }
+        }
+        return ti;
+}
+
+/*
+ * debugfs_printk - A function to write into the debugfs mount 'directly'
+ * using 'trace' infrastructure
+ * @dpk - Structure containing info such as parent_dir and directory
+ * @format - String containing format string specifiers
+ * @ap - List of arguments
+ */
+int debugfs_printk(struct debugfs_printk_data *dpk, char *format, ...)
+{
+	int ret;
+	struct trace_info *ti;
+	va_list(ap);
+	unsigned long flags;
+
+	va_start(ap, format);
+
+	ti = init_trace_interface(dpk);
+
+	/* Now do the actual printing */
+	/* Take an RCU Lock over the trace_info state */
+	rcu_read_lock();
+	/* Take a spinlock for the global buffer used by relay */
+	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
+		spin_lock_irqsave(&trace_lock, flags);
+	ret = trace_printf(ti, format, ap);
+	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
+		spin_unlock_irqrestore(&trace_lock, flags);
+	rcu_read_unlock();
+
+	va_end(ap);
+	return ret;
+}
+EXPORT_SYMBOL(debugfs_printk);
+
+/*
+ * debugfs_printk - A function to write into the debugfs mount 'directly'
+ * using 'trace' infrastructure
+ * @dpk - Structure containing info such as parent_dir and directory
+ * @output - Data that needs to be output
+ * @output_len - Length of the output data
+ */
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len)
+{
+	struct trace_info *ti;
+	char *record;
+
+	ti = init_trace_interface(dpk);
+
+	/* Now do the actual printing */
+	rcu_read_lock();
+	record = relay_reserve(ti->rchan, output_len);
+	if (record)
+		memcpy(record, output, output_len);
+	else
+		return -ENOMEM;
+	rcu_read_unlock();
+
+	return 0;
+}
+EXPORT_SYMBOL(debugfs_dump);
Index: linux-2.6.25-rc8-mm1/samples/trace/fork_new_trace.c
===================================================================
--- /dev/null
+++ linux-2.6.25-rc8-mm1/samples/trace/fork_new_trace.c
@@ -0,0 +1,97 @@
+/*
+ * An example of using trace in a kprobes module
+ *
+ * Copyright (C) 2007 IBM Inc.
+ *
+ * David Wilder <dwilder@us.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * -------
+ * This module creates a trace channel and places a kprobe
+ * on the function do_fork(). The value of current->pid is written to
+ * the trace channel each time the kprobe is hit..
+ *
+ * How to run the example:
+ * $ mount -t debugfs /debug
+ * $ insmod fork_trace.ko
+ *
+ * To view the data produced by the module:
+ * $ cat /debug/trace_example/do_fork/trace0
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/kprobes.h>
+#include <linux/trace.h>
+
+#define SAMPLE_PARENT_DIR "trace_new_example"
+#define PROBE_POINT "do_fork"
+
+static struct kprobe kp;
+static struct debugfs_printk_data *dpk;
+
+static int handler_pre(struct kprobe *p, struct pt_regs *regs)
+{
+	debugfs_printk(dpk, "%d\n", current->pid);
+	return 0;
+}
+
+int init_module(void)
+{
+	int ret = 0;
+	int len_parent_dir, len_dir;
+
+	/* setup the kprobe */
+	kp.pre_handler = handler_pre;
+	kp.post_handler = NULL;
+	kp.fault_handler = NULL;
+	kp.symbol_name = PROBE_POINT;
+	ret = register_kprobe(&kp);
+	if (ret) {
+		printk(KERN_ERR "fork_trace: register_kprobe failed\n");
+		return ret;
+	}
+
+	len_parent_dir = strlen(SAMPLE_PARENT_DIR) + 1;
+	/* Initialising len_dir to the larger of the two dir names */
+	len_dir = strlen("kprobe_struct") + 1;
+
+	dpk = kzalloc(sizeof(*dpk), GFP_KERNEL);
+	if(!dpk) ret = 1;
+
+	dpk->parent_dir = SAMPLE_PARENT_DIR;
+
+	/* Let's do a binary dump of struct kprobe using debugfs_dump */
+	dpk->dir = "kprobes_struct";
+	debugfs_dump(dpk, &kp, sizeof(kp));
+
+	/* Now change the directory to collect fork pid data */
+	dpk->dir = PROBE_POINT;
+
+	if(ret)
+		printk(KERN_ERR "Unable to find required free memory. "
+				"Trace new sample module loading aborted");
+	return ret;
+}
+
+void cleanup_module(void)
+{
+	unregister_kprobe(&kp);
+
+	/* Just a single cleanup call passing the parent dir string */
+	trace_cleanup_all(SAMPLE_PARENT_DIR);
+}
+MODULE_LICENSE("GPL");
Index: linux-2.6.25-rc8-mm1/samples/trace/Makefile
===================================================================
--- linux-2.6.25-rc8-mm1.orig/samples/trace/Makefile
+++ linux-2.6.25-rc8-mm1/samples/trace/Makefile
@@ -1,4 +1,4 @@
 # builds the trace example kernel modules;
 # then to use (as root):  insmod <fork_trace.ko>
 
-obj-$(CONFIG_SAMPLE_TRACE) := fork_trace.o
+obj-$(CONFIG_SAMPLE_TRACE) := fork_trace.o fork_new_trace.o
Index: linux-2.6.25-rc8-mm1/Documentation/trace.txt
===================================================================
--- linux-2.6.25-rc8-mm1.orig/Documentation/trace.txt
+++ linux-2.6.25-rc8-mm1/Documentation/trace.txt
@@ -150,6 +150,27 @@ The steps a kernel data provider takes t
 5) Destroy the trace channel and underlying relay channel -
    trace_cleanup().
 
+Alternatively the user may choose to make use of two new interfaces
+debugfs_printk() and debugfs_dump() to setup trace interface and
+trace_cleanup_all() to tear-down the same.
+
+Steps to use:
+1) Create and populate an instance of debugfs_printk_data structure. The fields
+   parent_dir and dir are mandatory. The fields buf_size, sub_buf_size and flags
+   are optional and will take default values if not populated. The field
+   'exists' is for the trace infrastructure to use.
+2) Default values for buf_size, sub_buf_size and flags are 4096, 40 and
+   TRACE_FLIGHT_CHANNEL respectively.
+3) Use debugfs_dump() to output binary data which may be acted upon by a
+   high-level program (say dumping a structure). debugfs_printk() can be used
+   for string output. Pass a pointer to the instance of debugfs_printk_data
+   structure to these functions along with other parameters. The output from
+   these functions can be found at
+   <debugfs_mount>/<parent_dir>/<dir>/trace<0..n>.
+4) trace_cleanup_all() for a given parent directory will cleanup and remove all
+   trace directories created under the specified directory.
+5) Sample code for the same can be found in samples/trace/fork_new_trace.c
+
 Kernel Configuration
 --------------------
 To use trace, configure your kernel with CONFIG_TRACE=y. Trace depends on

Re: [RFC Patch 1/1] debugfs_printk and debugfs_dump interface

[Randy Dunlap]

On Mon, 21 Apr 2008 18:13:29 +0530 K. Prasad wrote:

> This patch introduces two new interfaces called debugfs_printk and 
> debugfs_dump which can be used to print to the debugfs mount directly.
> It uses the 'trace' infrastructure underneath and is a patch over it.
> A sample file is also created to demonstrate its ease of use.
> 
> Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
> ---
>  Documentation/trace.txt        |   21 ++++
>  include/linux/trace.h          |   55 +++++++++++
>  lib/trace.c                    |  196 +++++++++++++++++++++++++++++++++++++++--
>  samples/trace/Makefile         |    2 
>  samples/trace/fork_new_trace.c |   97 ++++++++++++++++++++
>  5 files changed, 365 insertions(+), 6 deletions(-)

> Index: linux-2.6.25-rc8-mm1/lib/trace.c
> ===================================================================
> --- linux-2.6.25-rc8-mm1.orig/lib/trace.c
> +++ linux-2.6.25-rc8-mm1/lib/trace.c
> @@ -561,3 +609,141 @@ void trace_cleanup(struct trace_info *tr
>  	kfree(trace);
>  }
>  EXPORT_SYMBOL_GPL(trace_cleanup);
> +
> +/**
> + *	trace_cleanup_all - Removes all trace_info/directories created under a
> + *			    parent_dir

kernel-doc requires the "function name - description" to be on one line.
You could change the *<tab> to be *<space(s)>.

> + *	@parent_dir: Name of the parent directory
> + */
> +void trace_cleanup_all(const char *parent_dir)
> +{
> +	struct list_head *pos, *pos_temp;
> +	struct trace_dir *temp;
> +
> +	list_for_each_safe(pos, pos_temp, &trace_dirs) {
> +		temp = list_entry(pos, struct trace_dir, trace_dir_list);
> +		if (!strcmp(parent_dir, temp->trace_root->d_iname))
> +			trace_cleanup(temp->ti);
> +	}
> +}
> +EXPORT_SYMBOL_GPL(trace_cleanup_all);
> +
...
> +
> +/*
> + * debugfs_printk - A function to write into the debugfs mount 'directly'
> + * using 'trace' infrastructure
> + * @dpk - Structure containing info such as parent_dir and directory
> + * @format - String containing format string specifiers
> + * @ap - List of arguments

This one isn't quite kernel-doc notation, but it's very close to it,
and it should be kernel-doc since it's an exported symbol.
So it needs the following changes:

- begin with /**
- put function name + short description on one line
- use "@dpk: <description>" for function parameters (not "-")

> + */
> +int debugfs_printk(struct debugfs_printk_data *dpk, char *format, ...)
> +{
> +	int ret;
> +	struct trace_info *ti;
> +	va_list(ap);
> +	unsigned long flags;
> +
> +	va_start(ap, format);
> +
> +	ti = init_trace_interface(dpk);
> +
> +	/* Now do the actual printing */
> +	/* Take an RCU Lock over the trace_info state */
> +	rcu_read_lock();
> +	/* Take a spinlock for the global buffer used by relay */
> +	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
> +		spin_lock_irqsave(&trace_lock, flags);
> +	ret = trace_printf(ti, format, ap);
> +	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
> +		spin_unlock_irqrestore(&trace_lock, flags);
> +	rcu_read_unlock();
> +
> +	va_end(ap);
> +	return ret;
> +}
> +EXPORT_SYMBOL(debugfs_printk);
> +
> +/*
> + * debugfs_printk - A function to write into the debugfs mount 'directly'
> + * using 'trace' infrastructure
> + * @dpk - Structure containing info such as parent_dir and directory
> + * @output - Data that needs to be output
> + * @output_len - Length of the output data

Use kernel-doc notation.  Same comments as above.

> + */
> +int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
> +							const int output_len)
> +{
> +	struct trace_info *ti;
> +	char *record;
> +
> +	ti = init_trace_interface(dpk);
> +
> +	/* Now do the actual printing */
> +	rcu_read_lock();
> +	record = relay_reserve(ti->rchan, output_len);
> +	if (record)
> +		memcpy(record, output, output_len);
> +	else
> +		return -ENOMEM;
> +	rcu_read_unlock();
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(debugfs_dump);

> Index: linux-2.6.25-rc8-mm1/Documentation/trace.txt
> ===================================================================
> --- linux-2.6.25-rc8-mm1.orig/Documentation/trace.txt
> +++ linux-2.6.25-rc8-mm1/Documentation/trace.txt
> @@ -150,6 +150,27 @@ The steps a kernel data provider takes t
>  5) Destroy the trace channel and underlying relay channel -
>     trace_cleanup().
>  
> +Alternatively the user may choose to make use of two new interfaces

                                                    two new interfaces --

> +debugfs_printk() and debugfs_dump() to setup trace interface and

                    and debugfs_dump() -- to setup trace interfaces and

> +trace_cleanup_all() to tear-down the same.
> +
> +Steps to use:


---
~Randy

Re: [RFC Patch 1/1] debugfs_printk and debugfs_dump interface

[K. Prasad]

On Mon, Apr 21, 2008 at 10:14:03AM -0700, Randy Dunlap wrote:
> On Mon, 21 Apr 2008 18:13:29 +0530 K. Prasad wrote:
> 
> > This patch introduces two new interfaces called debugfs_printk and 
> > debugfs_dump which can be used to print to the debugfs mount directly.
> > It uses the 'trace' infrastructure underneath and is a patch over it.
> > A sample file is also created to demonstrate its ease of use.
> > 
> > Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
> > ---
> >  Documentation/trace.txt        |   21 ++++
> >  include/linux/trace.h          |   55 +++++++++++
> >  lib/trace.c                    |  196 +++++++++++++++++++++++++++++++++++++++--
> >  samples/trace/Makefile         |    2 
> >  samples/trace/fork_new_trace.c |   97 ++++++++++++++++++++
> >  5 files changed, 365 insertions(+), 6 deletions(-)
> 
> > Index: linux-2.6.25-rc8-mm1/lib/trace.c
> > ===================================================================
> > --- linux-2.6.25-rc8-mm1.orig/lib/trace.c
> > +++ linux-2.6.25-rc8-mm1/lib/trace.c
> > @@ -561,3 +609,141 @@ void trace_cleanup(struct trace_info *tr
> >  	kfree(trace);
> >  }
> >  EXPORT_SYMBOL_GPL(trace_cleanup);
> > +
> > +/**
> > + *	trace_cleanup_all - Removes all trace_info/directories created under a
> > + *			    parent_dir
> 
> kernel-doc requires the "function name - description" to be on one line.
> You could change the *<tab> to be *<space(s)>.
> 
> > + *	@parent_dir: Name of the parent directory
> > + */
> > +void trace_cleanup_all(const char *parent_dir)
> > +{
> > +	struct list_head *pos, *pos_temp;
> > +	struct trace_dir *temp;
> > +
> > +	list_for_each_safe(pos, pos_temp, &trace_dirs) {
> > +		temp = list_entry(pos, struct trace_dir, trace_dir_list);
> > +		if (!strcmp(parent_dir, temp->trace_root->d_iname))
> > +			trace_cleanup(temp->ti);
> > +	}
> > +}
> > +EXPORT_SYMBOL_GPL(trace_cleanup_all);
> > +
> ...
> > +
> > +/*
> > + * debugfs_printk - A function to write into the debugfs mount 'directly'
> > + * using 'trace' infrastructure
> > + * @dpk - Structure containing info such as parent_dir and directory
> > + * @format - String containing format string specifiers
> > + * @ap - List of arguments
> 
> This one isn't quite kernel-doc notation, but it's very close to it,
> and it should be kernel-doc since it's an exported symbol.
> So it needs the following changes:
> 
> - begin with /**
> - put function name + short description on one line
> - use "@dpk: <description>" for function parameters (not "-")
> 
> > + */
> > +int debugfs_printk(struct debugfs_printk_data *dpk, char *format, ...)
> > +{
> > +	int ret;
> > +	struct trace_info *ti;
> > +	va_list(ap);
> > +	unsigned long flags;
> > +
> > +	va_start(ap, format);
> > +
> > +	ti = init_trace_interface(dpk);
> > +
> > +	/* Now do the actual printing */
> > +	/* Take an RCU Lock over the trace_info state */
> > +	rcu_read_lock();
> > +	/* Take a spinlock for the global buffer used by relay */
> > +	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
> > +		spin_lock_irqsave(&trace_lock, flags);
> > +	ret = trace_printf(ti, format, ap);
> > +	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
> > +		spin_unlock_irqrestore(&trace_lock, flags);
> > +	rcu_read_unlock();
> > +
> > +	va_end(ap);
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL(debugfs_printk);
> > +
> > +/*
> > + * debugfs_printk - A function to write into the debugfs mount 'directly'
> > + * using 'trace' infrastructure
> > + * @dpk - Structure containing info such as parent_dir and directory
> > + * @output - Data that needs to be output
> > + * @output_len - Length of the output data
> 
> Use kernel-doc notation.  Same comments as above.
> 
> > + */
> > +int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
> > +							const int output_len)
> > +{
> > +	struct trace_info *ti;
> > +	char *record;
> > +
> > +	ti = init_trace_interface(dpk);
> > +
> > +	/* Now do the actual printing */
> > +	rcu_read_lock();
> > +	record = relay_reserve(ti->rchan, output_len);
> > +	if (record)
> > +		memcpy(record, output, output_len);
> > +	else
> > +		return -ENOMEM;
> > +	rcu_read_unlock();
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL(debugfs_dump);
> 
> > Index: linux-2.6.25-rc8-mm1/Documentation/trace.txt
> > ===================================================================
> > --- linux-2.6.25-rc8-mm1.orig/Documentation/trace.txt
> > +++ linux-2.6.25-rc8-mm1/Documentation/trace.txt
> > @@ -150,6 +150,27 @@ The steps a kernel data provider takes t
> >  5) Destroy the trace channel and underlying relay channel -
> >     trace_cleanup().
> >  
> > +Alternatively the user may choose to make use of two new interfaces
> 
>                                                     two new interfaces --
> 
> > +debugfs_printk() and debugfs_dump() to setup trace interface and
> 
>                     and debugfs_dump() -- to setup trace interfaces and
> 
> > +trace_cleanup_all() to tear-down the same.
> > +
> > +Steps to use:
> 
> 
> ---
> ~Randy

Thanks for the review Randy, and teaching me a thing of two about
kernel-doc notations!

Please find the revised patch below.


This patch introduces two new interfaces called debugfs_printk and 
debugfs_dump which can be used to print to the debugfs mount directly.
It uses the 'trace' infrastructure underneath and is a patch over it.
A sample file is also created to demonstrate its ease of use.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 Documentation/trace.txt        |   21 ++++
 include/linux/trace.h          |   55 +++++++++++
 lib/trace.c                    |  193 +++++++++++++++++++++++++++++++++++++++--
 samples/trace/Makefile         |    2 
 samples/trace/fork_new_trace.c |   97 ++++++++++++++++++++
 5 files changed, 362 insertions(+), 6 deletions(-)

Index: linux-2.6.25-rc8-mm1/include/linux/trace.h
===================================================================
--- linux-2.6.25-rc8-mm1.orig/include/linux/trace.h
+++ linux-2.6.25-rc8-mm1/include/linux/trace.h
@@ -39,10 +39,31 @@ enum trace_state {
 	TRACE_STOPPED,
 };
 
+enum trace_dir_state {
+	TRACE_PARENT_DIR_ABSENT,
+	TRACE_PARENT_DIR_EXISTS,
+	TRACE_DIR_EXISTS
+};
+
 #define TRACE_ROOT_NAME_SIZE	64	/* Max root dir identifier */
 #define TRACE_NAME_SIZE		64	/* Max trace identifier */
 
 /*
+ * Buffers for use by debugfs_printk
+ */
+#define DEFAULT_TRACE_BUF_SIZE 4096
+#define DEFAULT_TRACE_SUB_BUF_NR 40
+
+struct debugfs_printk_data {
+	char *parent_dir;
+	char *dir;
+	int exists;
+	int buf_size;
+	int sub_buf_size;
+	unsigned long flags;
+};
+
+/*
  * Global root user information
  */
 struct trace_root {
@@ -73,6 +94,17 @@ struct trace_info {
 	unsigned int buf_nr;
 };
 
+/*
+ * Information about every trace directory
+ */
+struct trace_dir {
+	struct list_head trace_dir_list;
+	char trace_dir_name[TRACE_NAME_SIZE];
+	struct dentry *trace_root;
+	struct dentry *trace_dir;
+	struct trace_info *ti;
+};
+
 #ifdef CONFIG_TRACE
 static inline int trace_running(struct trace_info *trace)
 {
@@ -83,6 +115,12 @@ struct trace_info *trace_setup(const cha
 int trace_start(struct trace_info *trace);
 int trace_stop(struct trace_info *trace);
 void trace_cleanup(struct trace_info *trace);
+int trace_exists(const char *parent_dir, const char *dir,
+					struct trace_info **ti);
+void trace_cleanup_all(const char *parent_dir);
+int debugfs_printk(struct debugfs_printk_data *dpk, char *format, ...);
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len);
 #else
 static inline struct trace_info *trace_setup(const char *root,
 					     const char *name, u32 buf_size,
@@ -94,6 +132,23 @@ static inline int trace_start(struct tra
 static inline int trace_stop(struct trace_info *trace) { return -EINVAL; }
 static inline int trace_running(struct trace_info *trace) { return 0; }
 static inline void trace_cleanup(struct trace_info *trace) {}
+static inline int trace_exists(const char *parent_dir, const char *dir,
+				struct trace_info **ti)
+{
+	return -EINVAL;
+}
+static inline void trace_cleanup_all(const char *parent_dir) {}
+static inline int debugfs_printk(struct debugfs_printk_data *dpk, char *format,
+				...)
+{
+	return -EINVAL;
+}
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len)
+{
+	return -EINVAL;
+}
+
 #endif
 
 #endif
Index: linux-2.6.25-rc8-mm1/lib/trace.c
===================================================================
--- linux-2.6.25-rc8-mm1.orig/lib/trace.c
+++ linux-2.6.25-rc8-mm1/lib/trace.c
@@ -29,7 +29,9 @@
 #include <linux/trace.h>
 
 static LIST_HEAD(trace_roots);
+static LIST_HEAD(trace_dirs);
 static DEFINE_MUTEX(trace_mutex);
+static DEFINE_SPINLOCK(trace_lock);
 
 static int state_open(struct inode *inode, struct file *filp)
 {
@@ -99,9 +101,19 @@ static void remove_root(struct trace_inf
 
 static void remove_tree(struct trace_info *trace)
 {
+	struct list_head *pos, *temp;
+	struct trace_dir *dr = NULL;
+
 	mutex_lock(&trace_mutex);
 	debugfs_remove(trace->dir);
 
+	list_for_each_safe(pos, temp, &trace_dirs) {
+		dr = list_entry(pos, struct trace_dir, trace_dir_list);
+		if (dr->ti == trace) {
+			list_del(pos);
+ 			kfree(dr);
+		}
+	}
 	if (trace->root) {
 		if (--trace->root->users == 0)
 			remove_root(trace);
@@ -142,11 +154,14 @@ static struct trace_root *lookup_root(co
 static struct dentry *create_tree(struct trace_info *trace, const char *root,
 				  const char *name)
 {
-	struct dentry *dir = NULL;
+	struct trace_dir *temp;
 
 	if (root == NULL || name == NULL)
 		return ERR_PTR(-EINVAL);
 
+	temp = kzalloc(sizeof(struct trace_dir), GFP_KERNEL);
+	strncpy(temp->trace_dir_name, name, strlen(name));
+
 	mutex_lock(&trace_mutex);
 
 	trace->root = lookup_root(root);
@@ -155,16 +170,49 @@ static struct dentry *create_tree(struct
 		goto err;
 	}
 
-	dir = debugfs_create_dir(name, trace->root->root);
-	if (IS_ERR(dir))
+	temp->trace_root = trace->root->root;
+	temp->trace_dir = debugfs_create_dir(name, trace->root->root);
+
+	if (IS_ERR(temp->trace_dir))
 		remove_root(trace);
-	else
+	else {
 		trace->root->users++;
+		temp->ti = trace;
+		list_add_tail(&temp->trace_dir_list, &trace_dirs);
+	}
 
 err:
 	mutex_unlock(&trace_mutex);
-	return dir;
+	return temp->trace_dir;
+}
+
+int trace_exists(const char *parent_dir, const char *dir,
+					struct trace_info **ti)
+{
+	struct list_head *pos;
+	struct trace_root *r;
+	struct trace_dir *temp;
+	int ret = TRACE_PARENT_DIR_ABSENT;
+
+	list_for_each(pos, &trace_roots) {
+		r = list_entry(pos, struct trace_root, list);
+		if (!strcmp(parent_dir, r->name))
+			goto search_dir;
+	}
+	return ret;
+
+ search_dir:
+	list_for_each(pos, &trace_dirs) {
+		temp = list_entry(pos, struct trace_dir, trace_dir_list);
+
+		if (!strcmp(dir, temp->trace_dir_name)) {
+			*ti = temp->ti;
+			return TRACE_DIR_EXISTS;
+		}
+	}
+	return TRACE_PARENT_DIR_EXISTS;
 }
+EXPORT_SYMBOL_GPL(trace_exists);
 
 static int dropped_open(struct inode *inode, struct file *filp)
 {
@@ -561,3 +609,138 @@ void trace_cleanup(struct trace_info *tr
 	kfree(trace);
 }
 EXPORT_SYMBOL_GPL(trace_cleanup);
+
+/**
+ *	trace_cleanup_all - Removes all trace directories under a parent_dir
+ *	@parent_dir: Name of the parent directory
+ */
+void trace_cleanup_all(const char *parent_dir)
+{
+	struct list_head *pos, *pos_temp;
+	struct trace_dir *temp;
+
+	list_for_each_safe(pos, pos_temp, &trace_dirs) {
+		temp = list_entry(pos, struct trace_dir, trace_dir_list);
+		if (!strcmp(parent_dir, temp->trace_root->d_iname))
+			trace_cleanup(temp->ti);
+	}
+}
+EXPORT_SYMBOL_GPL(trace_cleanup_all);
+
+/*
+ * Send formatted trace data to trace channel.
+ */
+static int trace_printf(struct trace_info *trace, const char *format,
+								va_list ap)
+{
+	va_list aq;
+	char *record;
+	int len;
+	int ret = 0;
+
+	if (trace_running(trace)) {
+		va_copy(aq, ap);
+		len = vsnprintf(NULL, 0, format, aq);
+		va_end(aq);
+		record = relay_reserve(trace->rchan, ++len);
+		if (record)
+			ret = vsnprintf(record, len, format, ap);
+	}
+	return ret;
+}
+
+static inline struct trace_info *init_trace_interface(struct
+                        			debugfs_printk_data *dpk)
+{
+        struct trace_info *ti;
+
+        dpk->exists = trace_exists(dpk->parent_dir, dpk->dir, &ti);
+
+        switch(dpk->exists) {
+
+        case TRACE_PARENT_DIR_EXISTS:
+        case TRACE_PARENT_DIR_ABSENT:
+                if(!dpk->buf_size)
+                        dpk->buf_size = DEFAULT_TRACE_BUF_SIZE;
+                if(!dpk->sub_buf_size)
+                        dpk->sub_buf_size = DEFAULT_TRACE_SUB_BUF_NR;
+                if(!dpk->flags)
+			dpk->flags = TRACE_FLIGHT_CHANNEL;
+                ti = trace_setup(dpk->parent_dir, dpk->dir,
+                        dpk->buf_size, dpk->sub_buf_size, dpk->flags);
+                printk(KERN_INFO "Trace interface %s setup through "
+                                                        "debugfs_printk\n",
+                                                        ti->dir->d_iname);
+                if (IS_ERR(ti)) {
+                        printk(KERN_ERR "Trace interface could not be "
+                        "initialised\n");
+                        return PTR_ERR(ti);
+                }
+                /* Fall through */
+        case TRACE_DIR_EXISTS:
+                if (ti->state != TRACE_RUNNING) {
+                        trace_start(ti);
+                }
+        }
+        return ti;
+}
+
+/**
+ * debugfs_printk - Output a string to debugfs mount 'directly' using 'trace'
+ * @dpk: Structure containing info such as parent_dir and directory
+ * @format: String containing format string specifiers
+ * @ap: List of arguments
+ */
+int debugfs_printk(struct debugfs_printk_data *dpk, char *format, ...)
+{
+	int ret;
+	struct trace_info *ti;
+	va_list(ap);
+	unsigned long flags;
+
+	va_start(ap, format);
+
+	ti = init_trace_interface(dpk);
+
+	/* Now do the actual printing */
+	/* Take an RCU Lock over the trace_info state */
+	rcu_read_lock();
+	/* Take a spinlock for the global buffer used by relay */
+	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
+		spin_lock_irqsave(&trace_lock, flags);
+	ret = trace_printf(ti, format, ap);
+	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
+		spin_unlock_irqrestore(&trace_lock, flags);
+	rcu_read_unlock();
+
+	va_end(ap);
+	return ret;
+}
+EXPORT_SYMBOL(debugfs_printk);
+
+/**
+ * debugfs_printk - Output binary into debugfs mount 'directly' using 'trace'
+ * @dpk: Structure containing info such as parent_dir and directory
+ * @output: Data that needs to be output
+ * @output_len: Length of the output data
+ */
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len)
+{
+	struct trace_info *ti;
+	char *record;
+
+	ti = init_trace_interface(dpk);
+
+	/* Now do the actual printing */
+	rcu_read_lock();
+	record = relay_reserve(ti->rchan, output_len);
+	if (record)
+		memcpy(record, output, output_len);
+	else
+		return -ENOMEM;
+	rcu_read_unlock();
+
+	return 0;
+}
+EXPORT_SYMBOL(debugfs_dump);
Index: linux-2.6.25-rc8-mm1/samples/trace/fork_new_trace.c
===================================================================
--- /dev/null
+++ linux-2.6.25-rc8-mm1/samples/trace/fork_new_trace.c
@@ -0,0 +1,97 @@
+/*
+ * An example of using trace in a kprobes module
+ *
+ * Copyright (C) 2007 IBM Inc.
+ *
+ * David Wilder <dwilder@us.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * -------
+ * This module creates a trace channel and places a kprobe
+ * on the function do_fork(). The value of current->pid is written to
+ * the trace channel each time the kprobe is hit..
+ *
+ * How to run the example:
+ * $ mount -t debugfs /debug
+ * $ insmod fork_trace.ko
+ *
+ * To view the data produced by the module:
+ * $ cat /debug/trace_example/do_fork/trace0
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/kprobes.h>
+#include <linux/trace.h>
+
+#define SAMPLE_PARENT_DIR "trace_new_example"
+#define PROBE_POINT "do_fork"
+
+static struct kprobe kp;
+static struct debugfs_printk_data *dpk;
+
+static int handler_pre(struct kprobe *p, struct pt_regs *regs)
+{
+	debugfs_printk(dpk, "%d\n", current->pid);
+	return 0;
+}
+
+int init_module(void)
+{
+	int ret = 0;
+	int len_parent_dir, len_dir;
+
+	/* setup the kprobe */
+	kp.pre_handler = handler_pre;
+	kp.post_handler = NULL;
+	kp.fault_handler = NULL;
+	kp.symbol_name = PROBE_POINT;
+	ret = register_kprobe(&kp);
+	if (ret) {
+		printk(KERN_ERR "fork_trace: register_kprobe failed\n");
+		return ret;
+	}
+
+	len_parent_dir = strlen(SAMPLE_PARENT_DIR) + 1;
+	/* Initialising len_dir to the larger of the two dir names */
+	len_dir = strlen("kprobe_struct") + 1;
+
+	dpk = kzalloc(sizeof(*dpk), GFP_KERNEL);
+	if(!dpk) ret = 1;
+
+	dpk->parent_dir = SAMPLE_PARENT_DIR;
+
+	/* Let's do a binary dump of struct kprobe using debugfs_dump */
+	dpk->dir = "kprobes_struct";
+	debugfs_dump(dpk, &kp, sizeof(kp));
+
+	/* Now change the directory to collect fork pid data */
+	dpk->dir = PROBE_POINT;
+
+	if(ret)
+		printk(KERN_ERR "Unable to find required free memory. "
+				"Trace new sample module loading aborted");
+	return ret;
+}
+
+void cleanup_module(void)
+{
+	unregister_kprobe(&kp);
+
+	/* Just a single cleanup call passing the parent dir string */
+	trace_cleanup_all(SAMPLE_PARENT_DIR);
+}
+MODULE_LICENSE("GPL");
Index: linux-2.6.25-rc8-mm1/samples/trace/Makefile
===================================================================
--- linux-2.6.25-rc8-mm1.orig/samples/trace/Makefile
+++ linux-2.6.25-rc8-mm1/samples/trace/Makefile
@@ -1,4 +1,4 @@
 # builds the trace example kernel modules;
 # then to use (as root):  insmod <fork_trace.ko>
 
-obj-$(CONFIG_SAMPLE_TRACE) := fork_trace.o
+obj-$(CONFIG_SAMPLE_TRACE) := fork_trace.o fork_new_trace.o
Index: linux-2.6.25-rc8-mm1/Documentation/trace.txt
===================================================================
--- linux-2.6.25-rc8-mm1.orig/Documentation/trace.txt
+++ linux-2.6.25-rc8-mm1/Documentation/trace.txt
@@ -150,6 +150,27 @@ The steps a kernel data provider takes t
 5) Destroy the trace channel and underlying relay channel -
    trace_cleanup().
 
+Alternatively the user may choose to make use of two new interfaces --
+debugfs_printk() and debugfs_dump() -- to setup trace interface and
+trace_cleanup_all() to tear-down the same.
+
+Steps to use:
+1) Create and populate an instance of debugfs_printk_data structure. The fields
+   parent_dir and dir are mandatory. The fields buf_size, sub_buf_size and flags
+   are optional and will take default values if not populated. The field
+   'exists' is for the trace infrastructure to use.
+2) Default values for buf_size, sub_buf_size and flags are 4096, 40 and
+   TRACE_FLIGHT_CHANNEL respectively.
+3) Use debugfs_dump() to output binary data which may be acted upon by a
+   high-level program (say dumping a structure). debugfs_printk() can be used
+   for string output. Pass a pointer to the instance of debugfs_printk_data
+   structure to these functions along with other parameters. The output from
+   these functions can be found at
+   <debugfs_mount>/<parent_dir>/<dir>/trace<0..n>.
+4) trace_cleanup_all() for a given parent directory will cleanup and remove all
+   trace directories created under the specified directory.
+5) Sample code for the same can be found in samples/trace/fork_new_trace.c
+
 Kernel Configuration
 --------------------
 To use trace, configure your kernel with CONFIG_TRACE=y. Trace depends on

Re: [RFC Patch 1/1] debugfs_printk and debugfs_dump interface

[Randy Dunlap]

K. Prasad wrote:

> This patch introduces two new interfaces called debugfs_printk and 
> debugfs_dump which can be used to print to the debugfs mount directly.
> It uses the 'trace' infrastructure underneath and is a patch over it.
> A sample file is also created to demonstrate its ease of use.
> 
> Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
> ---
>  Documentation/trace.txt        |   21 ++++
>  include/linux/trace.h          |   55 +++++++++++
>  lib/trace.c                    |  193 +++++++++++++++++++++++++++++++++++++++--
>  samples/trace/Makefile         |    2 
>  samples/trace/fork_new_trace.c |   97 ++++++++++++++++++++
>  5 files changed, 362 insertions(+), 6 deletions(-)

> +
> +/**
> + * debugfs_printk - Output binary into debugfs mount 'directly' using 'trace'

Oops. This is the debugfs_dump() function.

Otherwise it looks good.  Thanks.

> + * @dpk: Structure containing info such as parent_dir and directory
> + * @output: Data that needs to be output
> + * @output_len: Length of the output data
> + */
> +int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
> +							const int output_len)
> +{


-- 
~Randy

Re: [RFC Patch 1/1] debugfs_printk and debugfs_dump interface

[K. Prasad]

On Tue, Apr 22, 2008 at 07:53:33AM -0700, Randy Dunlap wrote:
> K. Prasad wrote:
> 
> >This patch introduces two new interfaces called debugfs_printk and 
> >debugfs_dump which can be used to print to the debugfs mount directly.
> >It uses the 'trace' infrastructure underneath and is a patch over it.
> >A sample file is also created to demonstrate its ease of use.
> >
> >Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
> >---
> > Documentation/trace.txt        |   21 ++++
> > include/linux/trace.h          |   55 +++++++++++
> > lib/trace.c                    |  193 
> > +++++++++++++++++++++++++++++++++++++++--
> > samples/trace/Makefile         |    2 
> > samples/trace/fork_new_trace.c |   97 ++++++++++++++++++++
> > 5 files changed, 362 insertions(+), 6 deletions(-)
> 
> >+
> >+/**
> >+ * debugfs_printk - Output binary into debugfs mount 'directly' using 
> >'trace'
> 
> Oops. This is the debugfs_dump() function.
Missed again. Sending the patch again with that minor change.
> 
> Otherwise it looks good.  Thanks.
> 
> >+ * @dpk: Structure containing info such as parent_dir and directory
> >+ * @output: Data that needs to be output
> >+ * @output_len: Length of the output data
> >+ */
> >+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
> >+							const int output_len)
> >+{
> 
> 
> -- 
> ~Randy


This patch introduces two new interfaces called debugfs_printk and 
debugfs_dump which can be used to print to the debugfs mount directly.
It uses the 'trace' infrastructure underneath and is a patch over it.
A sample file is also created to demonstrate its ease of use.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 Documentation/trace.txt        |   21 ++++
 include/linux/trace.h          |   55 +++++++++++
 lib/trace.c                    |  193 +++++++++++++++++++++++++++++++++++++++--
 samples/trace/Makefile         |    2 
 samples/trace/fork_new_trace.c |   97 ++++++++++++++++++++
 5 files changed, 362 insertions(+), 6 deletions(-)

Index: linux-2.6.25-rc8-mm1/include/linux/trace.h
===================================================================
--- linux-2.6.25-rc8-mm1.orig/include/linux/trace.h
+++ linux-2.6.25-rc8-mm1/include/linux/trace.h
@@ -39,10 +39,31 @@ enum trace_state {
 	TRACE_STOPPED,
 };
 
+enum trace_dir_state {
+	TRACE_PARENT_DIR_ABSENT,
+	TRACE_PARENT_DIR_EXISTS,
+	TRACE_DIR_EXISTS
+};
+
 #define TRACE_ROOT_NAME_SIZE	64	/* Max root dir identifier */
 #define TRACE_NAME_SIZE		64	/* Max trace identifier */
 
 /*
+ * Buffers for use by debugfs_printk
+ */
+#define DEFAULT_TRACE_BUF_SIZE 4096
+#define DEFAULT_TRACE_SUB_BUF_NR 40
+
+struct debugfs_printk_data {
+	char *parent_dir;
+	char *dir;
+	int exists;
+	int buf_size;
+	int sub_buf_size;
+	unsigned long flags;
+};
+
+/*
  * Global root user information
  */
 struct trace_root {
@@ -73,6 +94,17 @@ struct trace_info {
 	unsigned int buf_nr;
 };
 
+/*
+ * Information about every trace directory
+ */
+struct trace_dir {
+	struct list_head trace_dir_list;
+	char trace_dir_name[TRACE_NAME_SIZE];
+	struct dentry *trace_root;
+	struct dentry *trace_dir;
+	struct trace_info *ti;
+};
+
 #ifdef CONFIG_TRACE
 static inline int trace_running(struct trace_info *trace)
 {
@@ -83,6 +115,12 @@ struct trace_info *trace_setup(const cha
 int trace_start(struct trace_info *trace);
 int trace_stop(struct trace_info *trace);
 void trace_cleanup(struct trace_info *trace);
+int trace_exists(const char *parent_dir, const char *dir,
+					struct trace_info **ti);
+void trace_cleanup_all(const char *parent_dir);
+int debugfs_printk(struct debugfs_printk_data *dpk, char *format, ...);
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len);
 #else
 static inline struct trace_info *trace_setup(const char *root,
 					     const char *name, u32 buf_size,
@@ -94,6 +132,23 @@ static inline int trace_start(struct tra
 static inline int trace_stop(struct trace_info *trace) { return -EINVAL; }
 static inline int trace_running(struct trace_info *trace) { return 0; }
 static inline void trace_cleanup(struct trace_info *trace) {}
+static inline int trace_exists(const char *parent_dir, const char *dir,
+				struct trace_info **ti)
+{
+	return -EINVAL;
+}
+static inline void trace_cleanup_all(const char *parent_dir) {}
+static inline int debugfs_printk(struct debugfs_printk_data *dpk, char *format,
+				...)
+{
+	return -EINVAL;
+}
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len)
+{
+	return -EINVAL;
+}
+
 #endif
 
 #endif
Index: linux-2.6.25-rc8-mm1/lib/trace.c
===================================================================
--- linux-2.6.25-rc8-mm1.orig/lib/trace.c
+++ linux-2.6.25-rc8-mm1/lib/trace.c
@@ -29,7 +29,9 @@
 #include <linux/trace.h>
 
 static LIST_HEAD(trace_roots);
+static LIST_HEAD(trace_dirs);
 static DEFINE_MUTEX(trace_mutex);
+static DEFINE_SPINLOCK(trace_lock);
 
 static int state_open(struct inode *inode, struct file *filp)
 {
@@ -99,9 +101,19 @@ static void remove_root(struct trace_inf
 
 static void remove_tree(struct trace_info *trace)
 {
+	struct list_head *pos, *temp;
+	struct trace_dir *dr = NULL;
+
 	mutex_lock(&trace_mutex);
 	debugfs_remove(trace->dir);
 
+	list_for_each_safe(pos, temp, &trace_dirs) {
+		dr = list_entry(pos, struct trace_dir, trace_dir_list);
+		if (dr->ti == trace) {
+			list_del(pos);
+ 			kfree(dr);
+		}
+	}
 	if (trace->root) {
 		if (--trace->root->users == 0)
 			remove_root(trace);
@@ -142,11 +154,14 @@ static struct trace_root *lookup_root(co
 static struct dentry *create_tree(struct trace_info *trace, const char *root,
 				  const char *name)
 {
-	struct dentry *dir = NULL;
+	struct trace_dir *temp;
 
 	if (root == NULL || name == NULL)
 		return ERR_PTR(-EINVAL);
 
+	temp = kzalloc(sizeof(struct trace_dir), GFP_KERNEL);
+	strncpy(temp->trace_dir_name, name, strlen(name));
+
 	mutex_lock(&trace_mutex);
 
 	trace->root = lookup_root(root);
@@ -155,16 +170,49 @@ static struct dentry *create_tree(struct
 		goto err;
 	}
 
-	dir = debugfs_create_dir(name, trace->root->root);
-	if (IS_ERR(dir))
+	temp->trace_root = trace->root->root;
+	temp->trace_dir = debugfs_create_dir(name, trace->root->root);
+
+	if (IS_ERR(temp->trace_dir))
 		remove_root(trace);
-	else
+	else {
 		trace->root->users++;
+		temp->ti = trace;
+		list_add_tail(&temp->trace_dir_list, &trace_dirs);
+	}
 
 err:
 	mutex_unlock(&trace_mutex);
-	return dir;
+	return temp->trace_dir;
+}
+
+int trace_exists(const char *parent_dir, const char *dir,
+					struct trace_info **ti)
+{
+	struct list_head *pos;
+	struct trace_root *r;
+	struct trace_dir *temp;
+	int ret = TRACE_PARENT_DIR_ABSENT;
+
+	list_for_each(pos, &trace_roots) {
+		r = list_entry(pos, struct trace_root, list);
+		if (!strcmp(parent_dir, r->name))
+			goto search_dir;
+	}
+	return ret;
+
+ search_dir:
+	list_for_each(pos, &trace_dirs) {
+		temp = list_entry(pos, struct trace_dir, trace_dir_list);
+
+		if (!strcmp(dir, temp->trace_dir_name)) {
+			*ti = temp->ti;
+			return TRACE_DIR_EXISTS;
+		}
+	}
+	return TRACE_PARENT_DIR_EXISTS;
 }
+EXPORT_SYMBOL_GPL(trace_exists);
 
 static int dropped_open(struct inode *inode, struct file *filp)
 {
@@ -561,3 +609,138 @@ void trace_cleanup(struct trace_info *tr
 	kfree(trace);
 }
 EXPORT_SYMBOL_GPL(trace_cleanup);
+
+/**
+ *	trace_cleanup_all - Removes all trace directories under a parent_dir
+ *	@parent_dir: Name of the parent directory
+ */
+void trace_cleanup_all(const char *parent_dir)
+{
+	struct list_head *pos, *pos_temp;
+	struct trace_dir *temp;
+
+	list_for_each_safe(pos, pos_temp, &trace_dirs) {
+		temp = list_entry(pos, struct trace_dir, trace_dir_list);
+		if (!strcmp(parent_dir, temp->trace_root->d_iname))
+			trace_cleanup(temp->ti);
+	}
+}
+EXPORT_SYMBOL_GPL(trace_cleanup_all);
+
+/*
+ * Send formatted trace data to trace channel.
+ */
+static int trace_printf(struct trace_info *trace, const char *format,
+								va_list ap)
+{
+	va_list aq;
+	char *record;
+	int len;
+	int ret = 0;
+
+	if (trace_running(trace)) {
+		va_copy(aq, ap);
+		len = vsnprintf(NULL, 0, format, aq);
+		va_end(aq);
+		record = relay_reserve(trace->rchan, ++len);
+		if (record)
+			ret = vsnprintf(record, len, format, ap);
+	}
+	return ret;
+}
+
+static inline struct trace_info *init_trace_interface(struct
+                        			debugfs_printk_data *dpk)
+{
+        struct trace_info *ti;
+
+        dpk->exists = trace_exists(dpk->parent_dir, dpk->dir, &ti);
+
+        switch(dpk->exists) {
+
+        case TRACE_PARENT_DIR_EXISTS:
+        case TRACE_PARENT_DIR_ABSENT:
+                if(!dpk->buf_size)
+                        dpk->buf_size = DEFAULT_TRACE_BUF_SIZE;
+                if(!dpk->sub_buf_size)
+                        dpk->sub_buf_size = DEFAULT_TRACE_SUB_BUF_NR;
+                if(!dpk->flags)
+			dpk->flags = TRACE_FLIGHT_CHANNEL;
+                ti = trace_setup(dpk->parent_dir, dpk->dir,
+                        dpk->buf_size, dpk->sub_buf_size, dpk->flags);
+                printk(KERN_INFO "Trace interface %s setup through "
+                                                        "debugfs_printk\n",
+                                                        ti->dir->d_iname);
+                if (IS_ERR(ti)) {
+                        printk(KERN_ERR "Trace interface could not be "
+                        "initialised\n");
+                        return PTR_ERR(ti);
+                }
+                /* Fall through */
+        case TRACE_DIR_EXISTS:
+                if (ti->state != TRACE_RUNNING) {
+                        trace_start(ti);
+                }
+        }
+        return ti;
+}
+
+/**
+ * debugfs_printk - Output a string to debugfs mount 'directly' using 'trace'
+ * @dpk: Structure containing info such as parent_dir and directory
+ * @format: String containing format string specifiers
+ * @ap: List of arguments
+ */
+int debugfs_printk(struct debugfs_printk_data *dpk, char *format, ...)
+{
+	int ret;
+	struct trace_info *ti;
+	va_list(ap);
+	unsigned long flags;
+
+	va_start(ap, format);
+
+	ti = init_trace_interface(dpk);
+
+	/* Now do the actual printing */
+	/* Take an RCU Lock over the trace_info state */
+	rcu_read_lock();
+	/* Take a spinlock for the global buffer used by relay */
+	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
+		spin_lock_irqsave(&trace_lock, flags);
+	ret = trace_printf(ti, format, ap);
+	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
+		spin_unlock_irqrestore(&trace_lock, flags);
+	rcu_read_unlock();
+
+	va_end(ap);
+	return ret;
+}
+EXPORT_SYMBOL(debugfs_printk);
+
+/**
+ * debugfs_dump - Output binary into debugfs mount 'directly' using 'trace'
+ * @dpk: Structure containing info such as parent_dir and directory
+ * @output: Data that needs to be output
+ * @output_len: Length of the output data
+ */
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len)
+{
+	struct trace_info *ti;
+	char *record;
+
+	ti = init_trace_interface(dpk);
+
+	/* Now do the actual printing */
+	rcu_read_lock();
+	record = relay_reserve(ti->rchan, output_len);
+	if (record)
+		memcpy(record, output, output_len);
+	else
+		return -ENOMEM;
+	rcu_read_unlock();
+
+	return 0;
+}
+EXPORT_SYMBOL(debugfs_dump);
Index: linux-2.6.25-rc8-mm1/samples/trace/fork_new_trace.c
===================================================================
--- /dev/null
+++ linux-2.6.25-rc8-mm1/samples/trace/fork_new_trace.c
@@ -0,0 +1,97 @@
+/*
+ * An example of using trace in a kprobes module
+ *
+ * Copyright (C) 2007 IBM Inc.
+ *
+ * David Wilder <dwilder@us.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * -------
+ * This module creates a trace channel and places a kprobe
+ * on the function do_fork(). The value of current->pid is written to
+ * the trace channel each time the kprobe is hit..
+ *
+ * How to run the example:
+ * $ mount -t debugfs /debug
+ * $ insmod fork_trace.ko
+ *
+ * To view the data produced by the module:
+ * $ cat /debug/trace_example/do_fork/trace0
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/kprobes.h>
+#include <linux/trace.h>
+
+#define SAMPLE_PARENT_DIR "trace_new_example"
+#define PROBE_POINT "do_fork"
+
+static struct kprobe kp;
+static struct debugfs_printk_data *dpk;
+
+static int handler_pre(struct kprobe *p, struct pt_regs *regs)
+{
+	debugfs_printk(dpk, "%d\n", current->pid);
+	return 0;
+}
+
+int init_module(void)
+{
+	int ret = 0;
+	int len_parent_dir, len_dir;
+
+	/* setup the kprobe */
+	kp.pre_handler = handler_pre;
+	kp.post_handler = NULL;
+	kp.fault_handler = NULL;
+	kp.symbol_name = PROBE_POINT;
+	ret = register_kprobe(&kp);
+	if (ret) {
+		printk(KERN_ERR "fork_trace: register_kprobe failed\n");
+		return ret;
+	}
+
+	len_parent_dir = strlen(SAMPLE_PARENT_DIR) + 1;
+	/* Initialising len_dir to the larger of the two dir names */
+	len_dir = strlen("kprobe_struct") + 1;
+
+	dpk = kzalloc(sizeof(*dpk), GFP_KERNEL);
+	if(!dpk) ret = 1;
+
+	dpk->parent_dir = SAMPLE_PARENT_DIR;
+
+	/* Let's do a binary dump of struct kprobe using debugfs_dump */
+	dpk->dir = "kprobes_struct";
+	debugfs_dump(dpk, &kp, sizeof(kp));
+
+	/* Now change the directory to collect fork pid data */
+	dpk->dir = PROBE_POINT;
+
+	if(ret)
+		printk(KERN_ERR "Unable to find required free memory. "
+				"Trace new sample module loading aborted");
+	return ret;
+}
+
+void cleanup_module(void)
+{
+	unregister_kprobe(&kp);
+
+	/* Just a single cleanup call passing the parent dir string */
+	trace_cleanup_all(SAMPLE_PARENT_DIR);
+}
+MODULE_LICENSE("GPL");
Index: linux-2.6.25-rc8-mm1/samples/trace/Makefile
===================================================================
--- linux-2.6.25-rc8-mm1.orig/samples/trace/Makefile
+++ linux-2.6.25-rc8-mm1/samples/trace/Makefile
@@ -1,4 +1,4 @@
 # builds the trace example kernel modules;
 # then to use (as root):  insmod <fork_trace.ko>
 
-obj-$(CONFIG_SAMPLE_TRACE) := fork_trace.o
+obj-$(CONFIG_SAMPLE_TRACE) := fork_trace.o fork_new_trace.o
Index: linux-2.6.25-rc8-mm1/Documentation/trace.txt
===================================================================
--- linux-2.6.25-rc8-mm1.orig/Documentation/trace.txt
+++ linux-2.6.25-rc8-mm1/Documentation/trace.txt
@@ -150,6 +150,27 @@ The steps a kernel data provider takes t
 5) Destroy the trace channel and underlying relay channel -
    trace_cleanup().
 
+Alternatively the user may choose to make use of two new interfaces --
+debugfs_printk() and debugfs_dump() -- to setup trace interface and
+trace_cleanup_all() to tear-down the same.
+
+Steps to use:
+1) Create and populate an instance of debugfs_printk_data structure. The fields
+   parent_dir and dir are mandatory. The fields buf_size, sub_buf_size and flags
+   are optional and will take default values if not populated. The field
+   'exists' is for the trace infrastructure to use.
+2) Default values for buf_size, sub_buf_size and flags are 4096, 40 and
+   TRACE_FLIGHT_CHANNEL respectively.
+3) Use debugfs_dump() to output binary data which may be acted upon by a
+   high-level program (say dumping a structure). debugfs_printk() can be used
+   for string output. Pass a pointer to the instance of debugfs_printk_data
+   structure to these functions along with other parameters. The output from
+   these functions can be found at
+   <debugfs_mount>/<parent_dir>/<dir>/trace<0..n>.
+4) trace_cleanup_all() for a given parent directory will cleanup and remove all
+   trace directories created under the specified directory.
+5) Sample code for the same can be found in samples/trace/fork_new_trace.c
+
 Kernel Configuration
 --------------------
 To use trace, configure your kernel with CONFIG_TRACE=y. Trace depends on

Re: [RFC Patch 1/1] debugfs_printk and debugfs_dump interface

[David Wilder]

debugfs_print makes a great improvement to the trace interface.   I 
missing a couple of bugs the first time I reviewed it.  Please see my 
comments in-line.

Dave..


> +static inline struct trace_info *init_trace_interface(struct
> +                        			debugfs_printk_data *dpk)
> +{
> +        struct trace_info *ti;
> +
> +        dpk->exists = trace_exists(dpk->parent_dir, dpk->dir, &ti);
> +
> +        switch(dpk->exists) {
> +
> +        case TRACE_PARENT_DIR_EXISTS:
> +        case TRACE_PARENT_DIR_ABSENT:
> +                if(!dpk->buf_size)
> +                        dpk->buf_size = DEFAULT_TRACE_BUF_SIZE;
> +                if(!dpk->sub_buf_size)
> +                        dpk->sub_buf_size = DEFAULT_TRACE_SUB_BUF_NR;
> +                if(!dpk->flags)
> +			dpk->flags = TRACE_FLIGHT_CHANNEL;
> +                ti = trace_setup(dpk->parent_dir, dpk->dir,
> +                        dpk->buf_size, dpk->sub_buf_size, dpk->flags);
> +                printk(KERN_INFO "Trace interface %s setup through "
> +                                                        "debugfs_printk\n",
> +                                                        ti->dir->d_iname);
> +                if (IS_ERR(ti)) {
> +                        printk(KERN_ERR "Trace interface could not be "
> +                        "initialised\n");
> +                        return PTR_ERR(ti);
> +                }
> +                /* Fall through */
> +        case TRACE_DIR_EXISTS:
> +             if (ti->state != TRACE_RUNNING) {

You should start the trace only if the current state is TRACE_SETUP (I 
think).  See my comment in debugfs_print()


		  if (ti->state == TRACE_SETUP)
> +                        trace_start(ti);
> +                }
> +        }
> +        return ti;
> +}
> +
> +/*
> + * debugfs_printk - A function to write into the debugfs mount 'directly'
> + * using 'trace' infrastructure
> + * @dpk - Structure containing info such as parent_dir and directory
> + * @format - String containing format string specifiers
> + * @ap - List of arguments
> + */
> +int debugfs_printk(struct debugfs_printk_data *dpk, char *format, ...)
> +{
> +	int ret;
> +	struct trace_info *ti;
> +	va_list(ap);
> +	unsigned long flags;
> +
> +	va_start(ap, format);
> +
> +	ti = init_trace_interface(dpk);

init_trace_interface() alway sets trace->state to TRACE_RUNNING .  The 
results is that the user is prevented from stopping the trace.  You can 
see this in fork_new_trace.

$ cat debug/trace_new_example/do_fork/state
running
$ echo stop > debug/trace_new_example/do_fork/state
$ cat debug/trace_new_example/do_fork/state
running

> +
> +	/* Now do the actual printing */
> +	/* Take an RCU Lock over the trace_info state */
> +	rcu_read_lock();
> +	/* Take a spinlock for the global buffer used by relay */
> +	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
> +		spin_lock_irqsave(&trace_lock, flags);
> +	ret = trace_printf(ti, format, ap);
> +	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
> +		spin_unlock_irqrestore(&trace_lock, flags);
> +	rcu_read_unlock();
> +
> +	va_end(ap);
> +	return ret;
> +}
> +EXPORT_SYMBOL(debugfs_printk);
> +
> +/*
> + * debugfs_printk - A function to write into the debugfs mount 'directly'
> + * using 'trace' infrastructure
> + * @dpk - Structure containing info such as parent_dir and directory
> + * @output - Data that needs to be output
> + * @output_len - Length of the output data
> + */
> +int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
> +							const int output_len)
> +{
> +	struct trace_info *ti;
> +	char *record;
> +
> +	ti = init_trace_interface(dpk);

Same issue as debugfs_printf,

You should also check for trace_running as you did for trace_printf.


> +
> +	/* Now do the actual printing */
> +	rcu_read_lock();
> +	record = relay_reserve(ti->rchan, output_len);
> +	if (record)
> +		memcpy(record, output, output_len);
> +	else
> +		return -ENOMEM;
> +	rcu_read_unlock();
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(debugfs_dump);

Re: [RFC Patch 1/1] debugfs_printk and debugfs_dump interface

[K. Prasad]

On Thu, Apr 24, 2008 at 02:23:16PM -0700, David Wilder wrote:
> 
> debugfs_print makes a great improvement to the trace interface.   I 
Thanks.
> missing a couple of bugs the first time I reviewed it.  Please see my 
> comments in-line.
> 
> Dave..
> 
> 
> >+static inline struct trace_info *init_trace_interface(struct
> >+                        			debugfs_printk_data *dpk)
> >+{
> >+        struct trace_info *ti;
> >+
> >+        dpk->exists = trace_exists(dpk->parent_dir, dpk->dir, &ti);
> >+
> >+        switch(dpk->exists) {
> >+
> >+        case TRACE_PARENT_DIR_EXISTS:
> >+        case TRACE_PARENT_DIR_ABSENT:
> >+                if(!dpk->buf_size)
> >+                        dpk->buf_size = DEFAULT_TRACE_BUF_SIZE;
> >+                if(!dpk->sub_buf_size)
> >+                        dpk->sub_buf_size = DEFAULT_TRACE_SUB_BUF_NR;
> >+                if(!dpk->flags)
> >+			dpk->flags = TRACE_FLIGHT_CHANNEL;
> >+                ti = trace_setup(dpk->parent_dir, dpk->dir,
> >+                        dpk->buf_size, dpk->sub_buf_size, dpk->flags);
> >+                printk(KERN_INFO "Trace interface %s setup through "
> >+                                                        
> >"debugfs_printk\n",
> >+                                                        ti->dir->d_iname);
> >+                if (IS_ERR(ti)) {
> >+                        printk(KERN_ERR "Trace interface could not be "
> >+                        "initialised\n");
> >+                        return PTR_ERR(ti);
> >+                }
> >+                /* Fall through */
> >+        case TRACE_DIR_EXISTS:
> >+             if (ti->state != TRACE_RUNNING) {
> 
> You should start the trace only if the current state is TRACE_SETUP (I 
> think).  See my comment in debugfs_print()
> 
> 
> 		  if (ti->state == TRACE_SETUP)
> >+                        trace_start(ti);
> >+                }
> >+        }
> >+        return ti;
> >+}
> >+
> >+/*
> >+ * debugfs_printk - A function to write into the debugfs mount 'directly'
> >+ * using 'trace' infrastructure
> >+ * @dpk - Structure containing info such as parent_dir and directory
> >+ * @format - String containing format string specifiers
> >+ * @ap - List of arguments
> >+ */
> >+int debugfs_printk(struct debugfs_printk_data *dpk, char *format, ...)
> >+{
> >+	int ret;
> >+	struct trace_info *ti;
> >+	va_list(ap);
> >+	unsigned long flags;
> >+
> >+	va_start(ap, format);
> >+
> >+	ti = init_trace_interface(dpk);
> 
> init_trace_interface() alway sets trace->state to TRACE_RUNNING .  The 
> results is that the user is prevented from stopping the trace.  You can 
> see this in fork_new_trace.
This is actually an intentional design to guarantee that debugfs_* would
output the data overriding the control (the state was retained to enable
interoperability with other users of trace over the same parent_dir/dir
combination).

On further thought, it does make sense to enable the user to control the
output.

I will include your suggested changes.

> 
> $ cat debug/trace_new_example/do_fork/state
> running
> $ echo stop > debug/trace_new_example/do_fork/state
> $ cat debug/trace_new_example/do_fork/state
> running
> 
> >+
> >+	/* Now do the actual printing */
> >+	/* Take an RCU Lock over the trace_info state */
> >+	rcu_read_lock();
> >+	/* Take a spinlock for the global buffer used by relay */
> >+	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
> >+		spin_lock_irqsave(&trace_lock, flags);
> >+	ret = trace_printf(ti, format, ap);
> >+	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
> >+		spin_unlock_irqrestore(&trace_lock, flags);
> >+	rcu_read_unlock();
> >+
> >+	va_end(ap);
> >+	return ret;
> >+}
> >+EXPORT_SYMBOL(debugfs_printk);
> >+
> >+/*
> >+ * debugfs_printk - A function to write into the debugfs mount 'directly'
> >+ * using 'trace' infrastructure
> >+ * @dpk - Structure containing info such as parent_dir and directory
> >+ * @output - Data that needs to be output
> >+ * @output_len - Length of the output data
> >+ */
> >+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
> >+							const int output_len)
> >+{
> >+	struct trace_info *ti;
> >+	char *record;
> >+
> >+	ti = init_trace_interface(dpk);
> 
> Same issue as debugfs_printf,
> 
> You should also check for trace_running as you did for trace_printf.
Thanks for pointing this out. I missed it. I'm also enclosing the memcpy
with a spinlock if the TRACE_GLOBAL_CHANNEL flag is set.
Please find the new patch below.
> 
> 
> >+
> >+	/* Now do the actual printing */
> >+	rcu_read_lock();
> >+	record = relay_reserve(ti->rchan, output_len);
> >+	if (record)
> >+		memcpy(record, output, output_len);
> >+	else
> >+		return -ENOMEM;
> >+	rcu_read_unlock();
> >+
> >+	return 0;
> >+}
> >+EXPORT_SYMBOL(debugfs_dump);


This patch introduces two new interfaces called debugfs_printk and 
debugfs_dump which can be used to print to the debugfs mount directly.
It uses the 'trace' infrastructure underneath and is a patch over it.
A sample file is also created to demonstrate its ease of use.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 Documentation/trace.txt        |   21 ++++
 include/linux/trace.h          |   55 +++++++++++
 lib/trace.c                    |  202 +++++++++++++++++++++++++++++++++++++++--
 samples/trace/Makefile         |    2 
 samples/trace/fork_new_trace.c |   97 +++++++++++++++++++
 5 files changed, 371 insertions(+), 6 deletions(-)

Index: linux-2.6.25-rc8-mm1/include/linux/trace.h
===================================================================
--- linux-2.6.25-rc8-mm1.orig/include/linux/trace.h
+++ linux-2.6.25-rc8-mm1/include/linux/trace.h
@@ -39,10 +39,31 @@ enum trace_state {
 	TRACE_STOPPED,
 };
 
+enum trace_dir_state {
+	TRACE_PARENT_DIR_ABSENT,
+	TRACE_PARENT_DIR_EXISTS,
+	TRACE_DIR_EXISTS
+};
+
 #define TRACE_ROOT_NAME_SIZE	64	/* Max root dir identifier */
 #define TRACE_NAME_SIZE		64	/* Max trace identifier */
 
 /*
+ * Buffers for use by debugfs_printk
+ */
+#define DEFAULT_TRACE_BUF_SIZE 4096
+#define DEFAULT_TRACE_SUB_BUF_NR 40
+
+struct debugfs_printk_data {
+	char *parent_dir;
+	char *dir;
+	int exists;
+	int buf_size;
+	int sub_buf_size;
+	unsigned long flags;
+};
+
+/*
  * Global root user information
  */
 struct trace_root {
@@ -73,6 +94,17 @@ struct trace_info {
 	unsigned int buf_nr;
 };
 
+/*
+ * Information about every trace directory
+ */
+struct trace_dir {
+	struct list_head trace_dir_list;
+	char trace_dir_name[TRACE_NAME_SIZE];
+	struct dentry *trace_root;
+	struct dentry *trace_dir;
+	struct trace_info *ti;
+};
+
 #ifdef CONFIG_TRACE
 static inline int trace_running(struct trace_info *trace)
 {
@@ -83,6 +115,12 @@ struct trace_info *trace_setup(const cha
 int trace_start(struct trace_info *trace);
 int trace_stop(struct trace_info *trace);
 void trace_cleanup(struct trace_info *trace);
+int trace_exists(const char *parent_dir, const char *dir,
+					struct trace_info **ti);
+void trace_cleanup_all(const char *parent_dir);
+int debugfs_printk(struct debugfs_printk_data *dpk, char *format, ...);
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len);
 #else
 static inline struct trace_info *trace_setup(const char *root,
 					     const char *name, u32 buf_size,
@@ -94,6 +132,23 @@ static inline int trace_start(struct tra
 static inline int trace_stop(struct trace_info *trace) { return -EINVAL; }
 static inline int trace_running(struct trace_info *trace) { return 0; }
 static inline void trace_cleanup(struct trace_info *trace) {}
+static inline int trace_exists(const char *parent_dir, const char *dir,
+				struct trace_info **ti)
+{
+	return -EINVAL;
+}
+static inline void trace_cleanup_all(const char *parent_dir) {}
+static inline int debugfs_printk(struct debugfs_printk_data *dpk, char *format,
+				...)
+{
+	return -EINVAL;
+}
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len)
+{
+	return -EINVAL;
+}
+
 #endif
 
 #endif
Index: linux-2.6.25-rc8-mm1/lib/trace.c
===================================================================
--- linux-2.6.25-rc8-mm1.orig/lib/trace.c
+++ linux-2.6.25-rc8-mm1/lib/trace.c
@@ -29,7 +29,9 @@
 #include <linux/trace.h>
 
 static LIST_HEAD(trace_roots);
+static LIST_HEAD(trace_dirs);
 static DEFINE_MUTEX(trace_mutex);
+static DEFINE_SPINLOCK(trace_lock);
 
 static int state_open(struct inode *inode, struct file *filp)
 {
@@ -99,9 +101,19 @@ static void remove_root(struct trace_inf
 
 static void remove_tree(struct trace_info *trace)
 {
+	struct list_head *pos, *temp;
+	struct trace_dir *dr = NULL;
+
 	mutex_lock(&trace_mutex);
 	debugfs_remove(trace->dir);
 
+	list_for_each_safe(pos, temp, &trace_dirs) {
+		dr = list_entry(pos, struct trace_dir, trace_dir_list);
+		if (dr->ti == trace) {
+			list_del(pos);
+ 			kfree(dr);
+		}
+	}
 	if (trace->root) {
 		if (--trace->root->users == 0)
 			remove_root(trace);
@@ -142,11 +154,14 @@ static struct trace_root *lookup_root(co
 static struct dentry *create_tree(struct trace_info *trace, const char *root,
 				  const char *name)
 {
-	struct dentry *dir = NULL;
+	struct trace_dir *temp;
 
 	if (root == NULL || name == NULL)
 		return ERR_PTR(-EINVAL);
 
+	temp = kzalloc(sizeof(struct trace_dir), GFP_KERNEL);
+	strncpy(temp->trace_dir_name, name, strlen(name));
+
 	mutex_lock(&trace_mutex);
 
 	trace->root = lookup_root(root);
@@ -155,16 +170,49 @@ static struct dentry *create_tree(struct
 		goto err;
 	}
 
-	dir = debugfs_create_dir(name, trace->root->root);
-	if (IS_ERR(dir))
+	temp->trace_root = trace->root->root;
+	temp->trace_dir = debugfs_create_dir(name, trace->root->root);
+
+	if (IS_ERR(temp->trace_dir))
 		remove_root(trace);
-	else
+	else {
 		trace->root->users++;
+		temp->ti = trace;
+		list_add_tail(&temp->trace_dir_list, &trace_dirs);
+	}
 
 err:
 	mutex_unlock(&trace_mutex);
-	return dir;
+	return temp->trace_dir;
+}
+
+int trace_exists(const char *parent_dir, const char *dir,
+					struct trace_info **ti)
+{
+	struct list_head *pos;
+	struct trace_root *r;
+	struct trace_dir *temp;
+	int ret = TRACE_PARENT_DIR_ABSENT;
+
+	list_for_each(pos, &trace_roots) {
+		r = list_entry(pos, struct trace_root, list);
+		if (!strcmp(parent_dir, r->name))
+			goto search_dir;
+	}
+	return ret;
+
+ search_dir:
+	list_for_each(pos, &trace_dirs) {
+		temp = list_entry(pos, struct trace_dir, trace_dir_list);
+
+		if (!strcmp(dir, temp->trace_dir_name)) {
+			*ti = temp->ti;
+			return TRACE_DIR_EXISTS;
+		}
+	}
+	return TRACE_PARENT_DIR_EXISTS;
 }
+EXPORT_SYMBOL_GPL(trace_exists);
 
 static int dropped_open(struct inode *inode, struct file *filp)
 {
@@ -561,3 +609,147 @@ void trace_cleanup(struct trace_info *tr
 	kfree(trace);
 }
 EXPORT_SYMBOL_GPL(trace_cleanup);
+
+/**
+ *	trace_cleanup_all - Removes all trace directories under a parent_dir
+ *	@parent_dir: Name of the parent directory
+ */
+void trace_cleanup_all(const char *parent_dir)
+{
+	struct list_head *pos, *pos_temp;
+	struct trace_dir *temp;
+
+	list_for_each_safe(pos, pos_temp, &trace_dirs) {
+		temp = list_entry(pos, struct trace_dir, trace_dir_list);
+		if (!strcmp(parent_dir, temp->trace_root->d_iname))
+			trace_cleanup(temp->ti);
+	}
+}
+EXPORT_SYMBOL_GPL(trace_cleanup_all);
+
+/*
+ * Send formatted trace data to trace channel.
+ */
+static int trace_printf(struct trace_info *trace, const char *format,
+								va_list ap)
+{
+	va_list aq;
+	char *record;
+	int len;
+	int ret = 0;
+
+	if (trace_running(trace)) {
+		va_copy(aq, ap);
+		len = vsnprintf(NULL, 0, format, aq);
+		va_end(aq);
+		record = relay_reserve(trace->rchan, ++len);
+		if (record)
+			ret = vsnprintf(record, len, format, ap);
+	}
+	return ret;
+}
+
+static inline struct trace_info *init_trace_interface(struct
+                        			debugfs_printk_data *dpk)
+{
+        struct trace_info *ti;
+
+        dpk->exists = trace_exists(dpk->parent_dir, dpk->dir, &ti);
+
+        switch(dpk->exists) {
+
+        case TRACE_PARENT_DIR_EXISTS:
+        case TRACE_PARENT_DIR_ABSENT:
+                if(!dpk->buf_size)
+                        dpk->buf_size = DEFAULT_TRACE_BUF_SIZE;
+                if(!dpk->sub_buf_size)
+                        dpk->sub_buf_size = DEFAULT_TRACE_SUB_BUF_NR;
+                if(!dpk->flags)
+			dpk->flags = TRACE_FLIGHT_CHANNEL;
+                ti = trace_setup(dpk->parent_dir, dpk->dir,
+                        dpk->buf_size, dpk->sub_buf_size, dpk->flags);
+                printk(KERN_INFO "Trace interface %s setup through "
+                                                        "debugfs_printk\n",
+                                                        ti->dir->d_iname);
+                if (IS_ERR(ti)) {
+                        printk(KERN_ERR "Trace interface could not be "
+                        "initialised\n");
+                        return PTR_ERR(ti);
+                }
+                /* Fall through */
+        case TRACE_DIR_EXISTS:
+                if (ti->state != TRACE_RUNNING) {
+                        trace_start(ti);
+                }
+        }
+        return ti;
+}
+
+/**
+ * debugfs_printk - Output a string to debugfs mount 'directly' using 'trace'
+ * @dpk: Structure containing info such as parent_dir and directory
+ * @format: String containing format string specifiers
+ * @ap: List of arguments
+ */
+int debugfs_printk(struct debugfs_printk_data *dpk, char *format, ...)
+{
+	int ret;
+	struct trace_info *ti;
+	va_list(ap);
+	unsigned long flags;
+
+	va_start(ap, format);
+
+	ti = init_trace_interface(dpk);
+
+	/* Now do the actual printing */
+	/* Take an RCU Lock over the trace_info state */
+	rcu_read_lock();
+	/* Take a spinlock for the global buffer used by relay */
+	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
+		spin_lock_irqsave(&trace_lock, flags);
+	ret = trace_printf(ti, format, ap);
+	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
+		spin_unlock_irqrestore(&trace_lock, flags);
+	rcu_read_unlock();
+
+	va_end(ap);
+	return ret;
+}
+EXPORT_SYMBOL(debugfs_printk);
+
+/**
+ * debugfs_dump - Output binary into debugfs mount 'directly' using 'trace'
+ * @dpk: Structure containing info such as parent_dir and directory
+ * @output: Data that needs to be output
+ * @output_len: Length of the output data
+ */
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len)
+{
+	struct trace_info *ti;
+	char *record;
+	unsigned long flags;
+	int ret = 0;
+
+	ti = init_trace_interface(dpk);
+
+	/* Now do the actual printing */
+	rcu_read_lock();
+	/* Take a spinlock for the global buffer used by relay */
+	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
+		spin_lock_irqsave(&trace_lock, flags);
+	record = relay_reserve(ti->rchan, output_len);
+
+	if (record && trace_running(trace))
+		memcpy(record, output, output_len);
+	else
+		ret = -ENOMEM;
+
+	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
+		spin_unlock_irqrestore(&trace_lock, flags);
+	rcu_read_unlock();
+
+	return ret;
+}
+EXPORT_SYMBOL(debugfs_dump);
Index: linux-2.6.25-rc8-mm1/samples/trace/fork_new_trace.c
===================================================================
--- /dev/null
+++ linux-2.6.25-rc8-mm1/samples/trace/fork_new_trace.c
@@ -0,0 +1,97 @@
+/*
+ * An example of using trace in a kprobes module
+ *
+ * Copyright (C) 2007 IBM Inc.
+ *
+ * David Wilder <dwilder@us.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * -------
+ * This module creates a trace channel and places a kprobe
+ * on the function do_fork(). The value of current->pid is written to
+ * the trace channel each time the kprobe is hit..
+ *
+ * How to run the example:
+ * $ mount -t debugfs /debug
+ * $ insmod fork_trace.ko
+ *
+ * To view the data produced by the module:
+ * $ cat /debug/trace_example/do_fork/trace0
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/kprobes.h>
+#include <linux/trace.h>
+
+#define SAMPLE_PARENT_DIR "trace_new_example"
+#define PROBE_POINT "do_fork"
+
+static struct kprobe kp;
+static struct debugfs_printk_data *dpk;
+
+static int handler_pre(struct kprobe *p, struct pt_regs *regs)
+{
+	debugfs_printk(dpk, "%d\n", current->pid);
+	return 0;
+}
+
+int init_module(void)
+{
+	int ret = 0;
+	int len_parent_dir, len_dir;
+
+	/* setup the kprobe */
+	kp.pre_handler = handler_pre;
+	kp.post_handler = NULL;
+	kp.fault_handler = NULL;
+	kp.symbol_name = PROBE_POINT;
+	ret = register_kprobe(&kp);
+	if (ret) {
+		printk(KERN_ERR "fork_trace: register_kprobe failed\n");
+		return ret;
+	}
+
+	len_parent_dir = strlen(SAMPLE_PARENT_DIR) + 1;
+	/* Initialising len_dir to the larger of the two dir names */
+	len_dir = strlen("kprobe_struct") + 1;
+
+	dpk = kzalloc(sizeof(*dpk), GFP_KERNEL);
+	if(!dpk) ret = 1;
+
+	dpk->parent_dir = SAMPLE_PARENT_DIR;
+
+	/* Let's do a binary dump of struct kprobe using debugfs_dump */
+	dpk->dir = "kprobes_struct";
+	debugfs_dump(dpk, &kp, sizeof(kp));
+
+	/* Now change the directory to collect fork pid data */
+	dpk->dir = PROBE_POINT;
+
+	if(ret)
+		printk(KERN_ERR "Unable to find required free memory. "
+				"Trace new sample module loading aborted");
+	return ret;
+}
+
+void cleanup_module(void)
+{
+	unregister_kprobe(&kp);
+
+	/* Just a single cleanup call passing the parent dir string */
+	trace_cleanup_all(SAMPLE_PARENT_DIR);
+}
+MODULE_LICENSE("GPL");
Index: linux-2.6.25-rc8-mm1/samples/trace/Makefile
===================================================================
--- linux-2.6.25-rc8-mm1.orig/samples/trace/Makefile
+++ linux-2.6.25-rc8-mm1/samples/trace/Makefile
@@ -1,4 +1,4 @@
 # builds the trace example kernel modules;
 # then to use (as root):  insmod <fork_trace.ko>
 
-obj-$(CONFIG_SAMPLE_TRACE) := fork_trace.o
+obj-$(CONFIG_SAMPLE_TRACE) := fork_trace.o fork_new_trace.o
Index: linux-2.6.25-rc8-mm1/Documentation/trace.txt
===================================================================
--- linux-2.6.25-rc8-mm1.orig/Documentation/trace.txt
+++ linux-2.6.25-rc8-mm1/Documentation/trace.txt
@@ -150,6 +150,27 @@ The steps a kernel data provider takes t
 5) Destroy the trace channel and underlying relay channel -
    trace_cleanup().
 
+Alternatively the user may choose to make use of two new interfaces --
+debugfs_printk() and debugfs_dump() -- to setup trace interface and
+trace_cleanup_all() to tear-down the same.
+
+Steps to use:
+1) Create and populate an instance of debugfs_printk_data structure. The fields
+   parent_dir and dir are mandatory. The fields buf_size, sub_buf_size and flags
+   are optional and will take default values if not populated. The field
+   'exists' is for the trace infrastructure to use.
+2) Default values for buf_size, sub_buf_size and flags are 4096, 40 and
+   TRACE_FLIGHT_CHANNEL respectively.
+3) Use debugfs_dump() to output binary data which may be acted upon by a
+   high-level program (say dumping a structure). debugfs_printk() can be used
+   for string output. Pass a pointer to the instance of debugfs_printk_data
+   structure to these functions along with other parameters. The output from
+   these functions can be found at
+   <debugfs_mount>/<parent_dir>/<dir>/trace<0..n>.
+4) trace_cleanup_all() for a given parent directory will cleanup and remove all
+   trace directories created under the specified directory.
+5) Sample code for the same can be found in samples/trace/fork_new_trace.c
+
 Kernel Configuration
 --------------------
 To use trace, configure your kernel with CONFIG_TRACE=y. Trace depends on

Re: [RFC Patch 1/1] debugfs_printk and debugfs_dump interface

[K. Prasad]

On Fri, Apr 25, 2008 at 01:12:00PM +0530, K. Prasad wrote:
> Please find the new patch below.
> > 
Let the email slip through a little early. Please find the revised
patch below.

Thanks,
K.Prasad

This patch introduces two new interfaces called debugfs_printk and 
debugfs_dump which can be used to print to the debugfs mount directly.
It uses the 'trace' infrastructure underneath and is a patch over it.
A sample file is also created to demonstrate its ease of use.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 Documentation/trace.txt        |   21 ++++
 include/linux/trace.h          |   55 +++++++++++
 lib/trace.c                    |  202 +++++++++++++++++++++++++++++++++++++++--
 samples/trace/Makefile         |    2 
 samples/trace/fork_new_trace.c |   97 +++++++++++++++++++
 5 files changed, 371 insertions(+), 6 deletions(-)

Index: linux-2.6.25-rc8-mm1/include/linux/trace.h
===================================================================
--- linux-2.6.25-rc8-mm1.orig/include/linux/trace.h
+++ linux-2.6.25-rc8-mm1/include/linux/trace.h
@@ -39,10 +39,31 @@ enum trace_state {
 	TRACE_STOPPED,
 };
 
+enum trace_dir_state {
+	TRACE_PARENT_DIR_ABSENT,
+	TRACE_PARENT_DIR_EXISTS,
+	TRACE_DIR_EXISTS
+};
+
 #define TRACE_ROOT_NAME_SIZE	64	/* Max root dir identifier */
 #define TRACE_NAME_SIZE		64	/* Max trace identifier */
 
 /*
+ * Buffers for use by debugfs_printk
+ */
+#define DEFAULT_TRACE_BUF_SIZE 4096
+#define DEFAULT_TRACE_SUB_BUF_NR 40
+
+struct debugfs_printk_data {
+	char *parent_dir;
+	char *dir;
+	int exists;
+	int buf_size;
+	int sub_buf_size;
+	unsigned long flags;
+};
+
+/*
  * Global root user information
  */
 struct trace_root {
@@ -73,6 +94,17 @@ struct trace_info {
 	unsigned int buf_nr;
 };
 
+/*
+ * Information about every trace directory
+ */
+struct trace_dir {
+	struct list_head trace_dir_list;
+	char trace_dir_name[TRACE_NAME_SIZE];
+	struct dentry *trace_root;
+	struct dentry *trace_dir;
+	struct trace_info *ti;
+};
+
 #ifdef CONFIG_TRACE
 static inline int trace_running(struct trace_info *trace)
 {
@@ -83,6 +115,12 @@ struct trace_info *trace_setup(const cha
 int trace_start(struct trace_info *trace);
 int trace_stop(struct trace_info *trace);
 void trace_cleanup(struct trace_info *trace);
+int trace_exists(const char *parent_dir, const char *dir,
+					struct trace_info **ti);
+void trace_cleanup_all(const char *parent_dir);
+int debugfs_printk(struct debugfs_printk_data *dpk, char *format, ...);
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len);
 #else
 static inline struct trace_info *trace_setup(const char *root,
 					     const char *name, u32 buf_size,
@@ -94,6 +132,23 @@ static inline int trace_start(struct tra
 static inline int trace_stop(struct trace_info *trace) { return -EINVAL; }
 static inline int trace_running(struct trace_info *trace) { return 0; }
 static inline void trace_cleanup(struct trace_info *trace) {}
+static inline int trace_exists(const char *parent_dir, const char *dir,
+				struct trace_info **ti)
+{
+	return -EINVAL;
+}
+static inline void trace_cleanup_all(const char *parent_dir) {}
+static inline int debugfs_printk(struct debugfs_printk_data *dpk, char *format,
+				...)
+{
+	return -EINVAL;
+}
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len)
+{
+	return -EINVAL;
+}
+
 #endif
 
 #endif
Index: linux-2.6.25-rc8-mm1/lib/trace.c
===================================================================
--- linux-2.6.25-rc8-mm1.orig/lib/trace.c
+++ linux-2.6.25-rc8-mm1/lib/trace.c
@@ -29,7 +29,9 @@
 #include <linux/trace.h>
 
 static LIST_HEAD(trace_roots);
+static LIST_HEAD(trace_dirs);
 static DEFINE_MUTEX(trace_mutex);
+static DEFINE_SPINLOCK(trace_lock);
 
 static int state_open(struct inode *inode, struct file *filp)
 {
@@ -99,9 +101,19 @@ static void remove_root(struct trace_inf
 
 static void remove_tree(struct trace_info *trace)
 {
+	struct list_head *pos, *temp;
+	struct trace_dir *dr = NULL;
+
 	mutex_lock(&trace_mutex);
 	debugfs_remove(trace->dir);
 
+	list_for_each_safe(pos, temp, &trace_dirs) {
+		dr = list_entry(pos, struct trace_dir, trace_dir_list);
+		if (dr->ti == trace) {
+			list_del(pos);
+ 			kfree(dr);
+		}
+	}
 	if (trace->root) {
 		if (--trace->root->users == 0)
 			remove_root(trace);
@@ -142,11 +154,14 @@ static struct trace_root *lookup_root(co
 static struct dentry *create_tree(struct trace_info *trace, const char *root,
 				  const char *name)
 {
-	struct dentry *dir = NULL;
+	struct trace_dir *temp;
 
 	if (root == NULL || name == NULL)
 		return ERR_PTR(-EINVAL);
 
+	temp = kzalloc(sizeof(struct trace_dir), GFP_KERNEL);
+	strncpy(temp->trace_dir_name, name, strlen(name));
+
 	mutex_lock(&trace_mutex);
 
 	trace->root = lookup_root(root);
@@ -155,17 +170,50 @@ static struct dentry *create_tree(struct
 		goto err;
 	}
 
-	dir = debugfs_create_dir(name, trace->root->root);
-	if (IS_ERR(dir))
+	temp->trace_root = trace->root->root;
+	temp->trace_dir = debugfs_create_dir(name, trace->root->root);
+
+	if (IS_ERR(temp->trace_dir))
 		remove_root(trace);
-	else
+	else {
 		trace->root->users++;
+		temp->ti = trace;
+		list_add_tail(&temp->trace_dir_list, &trace_dirs);
+	}
 
 err:
 	mutex_unlock(&trace_mutex);
-	return dir;
+	return temp->trace_dir;
 }
 
+int trace_exists(const char *parent_dir, const char *dir,
+					struct trace_info **ti)
+{
+	struct list_head *pos;
+	struct trace_root *r;
+	struct trace_dir *temp;
+	int ret = TRACE_PARENT_DIR_ABSENT;
+
+	list_for_each(pos, &trace_roots) {
+		r = list_entry(pos, struct trace_root, list);
+		if (!strcmp(parent_dir, r->name))
+			goto search_dir;
+	}
+	return ret;
+
+ search_dir:
+	list_for_each(pos, &trace_dirs) {
+		temp = list_entry(pos, struct trace_dir, trace_dir_list);
+
+		if (!strcmp(dir, temp->trace_dir_name)) {
+			*ti = temp->ti;
+			return TRACE_DIR_EXISTS;
+		}
+	}
+	return TRACE_PARENT_DIR_EXISTS;
+}
+EXPORT_SYMBOL_GPL(trace_exists);
+
 static int dropped_open(struct inode *inode, struct file *filp)
 {
 	filp->private_data = inode->i_private;
@@ -561,3 +609,147 @@ void trace_cleanup(struct trace_info *tr
 	kfree(trace);
 }
 EXPORT_SYMBOL_GPL(trace_cleanup);
+
+/**
+ *	trace_cleanup_all - Removes all trace directories under a parent_dir
+ *	@parent_dir: Name of the parent directory
+ */
+void trace_cleanup_all(const char *parent_dir)
+{
+	struct list_head *pos, *pos_temp;
+	struct trace_dir *temp;
+
+	list_for_each_safe(pos, pos_temp, &trace_dirs) {
+		temp = list_entry(pos, struct trace_dir, trace_dir_list);
+		if (!strcmp(parent_dir, temp->trace_root->d_iname))
+			trace_cleanup(temp->ti);
+	}
+}
+EXPORT_SYMBOL_GPL(trace_cleanup_all);
+
+/*
+ * Send formatted trace data to trace channel.
+ */
+static int trace_printf(struct trace_info *trace, const char *format,
+								va_list ap)
+{
+	va_list aq;
+	char *record;
+	int len;
+	int ret = 0;
+
+	if (trace_running(trace)) {
+		va_copy(aq, ap);
+		len = vsnprintf(NULL, 0, format, aq);
+		va_end(aq);
+		record = relay_reserve(trace->rchan, ++len);
+		if (record)
+			ret = vsnprintf(record, len, format, ap);
+	}
+	return ret;
+}
+
+static inline struct trace_info *init_trace_interface(struct
+                        			debugfs_printk_data *dpk)
+{
+        struct trace_info *ti;
+
+        dpk->exists = trace_exists(dpk->parent_dir, dpk->dir, &ti);
+
+        switch(dpk->exists) {
+
+        case TRACE_PARENT_DIR_EXISTS:
+        case TRACE_PARENT_DIR_ABSENT:
+                if(!dpk->buf_size)
+                        dpk->buf_size = DEFAULT_TRACE_BUF_SIZE;
+                if(!dpk->sub_buf_size)
+                        dpk->sub_buf_size = DEFAULT_TRACE_SUB_BUF_NR;
+                if(!dpk->flags)
+			dpk->flags = TRACE_FLIGHT_CHANNEL;
+                ti = trace_setup(dpk->parent_dir, dpk->dir,
+                        dpk->buf_size, dpk->sub_buf_size, dpk->flags);
+                printk(KERN_INFO "Trace interface %s setup through "
+                                                        "debugfs_printk\n",
+                                                        ti->dir->d_iname);
+                if (IS_ERR(ti)) {
+                        printk(KERN_ERR "Trace interface could not be "
+                        "initialised\n");
+                        return PTR_ERR(ti);
+                }
+                /* Fall through */
+        case TRACE_DIR_EXISTS:
+                if (ti->state == TRACE_SETUP) {
+                        trace_start(ti);
+                }
+        }
+        return ti;
+}
+
+/**
+ * debugfs_printk - Output a string to debugfs mount 'directly' using 'trace'
+ * @dpk: Structure containing info such as parent_dir and directory
+ * @format: String containing format string specifiers
+ * @ap: List of arguments
+ */
+int debugfs_printk(struct debugfs_printk_data *dpk, char *format, ...)
+{
+	int ret;
+	struct trace_info *ti;
+	va_list(ap);
+	unsigned long flags;
+
+	va_start(ap, format);
+
+	ti = init_trace_interface(dpk);
+
+	/* Now do the actual printing */
+	/* Take an RCU Lock over the trace_info state */
+	rcu_read_lock();
+	/* Take a spinlock for the global buffer used by relay */
+	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
+		spin_lock_irqsave(&trace_lock, flags);
+	ret = trace_printf(ti, format, ap);
+	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
+		spin_unlock_irqrestore(&trace_lock, flags);
+	rcu_read_unlock();
+
+	va_end(ap);
+	return ret;
+}
+EXPORT_SYMBOL(debugfs_printk);
+
+/**
+ * debugfs_dump - Output binary into debugfs mount 'directly' using 'trace'
+ * @dpk: Structure containing info such as parent_dir and directory
+ * @output: Data that needs to be output
+ * @output_len: Length of the output data
+ */
+int debugfs_dump(struct debugfs_printk_data *dpk, const void *output,
+							const int output_len)
+{
+	struct trace_info *ti;
+	char *record;
+	unsigned long flags;
+	int ret = 0;
+
+	ti = init_trace_interface(dpk);
+
+	/* Now do the actual printing */
+	rcu_read_lock();
+	/* Take a spinlock for the global buffer used by relay */
+	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
+		spin_lock_irqsave(&trace_lock, flags);
+	record = relay_reserve(ti->rchan, output_len);
+
+	if (record && trace_running(trace))
+		memcpy(record, output, output_len);
+	else
+		record ? ret = -EPERM : ret = -ENOMEM;
+
+	if (dpk->flags & TRACE_GLOBAL_CHANNEL)
+		spin_unlock_irqrestore(&trace_lock, flags);
+	rcu_read_unlock();
+
+	return ret;
+}
+EXPORT_SYMBOL(debugfs_dump);
Index: linux-2.6.25-rc8-mm1/samples/trace/fork_new_trace.c
===================================================================
--- /dev/null
+++ linux-2.6.25-rc8-mm1/samples/trace/fork_new_trace.c
@@ -0,0 +1,97 @@
+/*
+ * An example of using trace in a kprobes module
+ *
+ * Copyright (C) 2007 IBM Inc.
+ *
+ * David Wilder <dwilder@us.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * -------
+ * This module creates a trace channel and places a kprobe
+ * on the function do_fork(). The value of current->pid is written to
+ * the trace channel each time the kprobe is hit..
+ *
+ * How to run the example:
+ * $ mount -t debugfs /debug
+ * $ insmod fork_trace.ko
+ *
+ * To view the data produced by the module:
+ * $ cat /debug/trace_example/do_fork/trace0
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/kprobes.h>
+#include <linux/trace.h>
+
+#define SAMPLE_PARENT_DIR "trace_new_example"
+#define PROBE_POINT "do_fork"
+
+static struct kprobe kp;
+static struct debugfs_printk_data *dpk;
+
+static int handler_pre(struct kprobe *p, struct pt_regs *regs)
+{
+	debugfs_printk(dpk, "%d\n", current->pid);
+	return 0;
+}
+
+int init_module(void)
+{
+	int ret = 0;
+	int len_parent_dir, len_dir;
+
+	/* setup the kprobe */
+	kp.pre_handler = handler_pre;
+	kp.post_handler = NULL;
+	kp.fault_handler = NULL;
+	kp.symbol_name = PROBE_POINT;
+	ret = register_kprobe(&kp);
+	if (ret) {
+		printk(KERN_ERR "fork_trace: register_kprobe failed\n");
+		return ret;
+	}
+
+	len_parent_dir = strlen(SAMPLE_PARENT_DIR) + 1;
+	/* Initialising len_dir to the larger of the two dir names */
+	len_dir = strlen("kprobe_struct") + 1;
+
+	dpk = kzalloc(sizeof(*dpk), GFP_KERNEL);
+	if(!dpk) ret = 1;
+
+	dpk->parent_dir = SAMPLE_PARENT_DIR;
+
+	/* Let's do a binary dump of struct kprobe using debugfs_dump */
+	dpk->dir = "kprobes_struct";
+	debugfs_dump(dpk, &kp, sizeof(kp));
+
+	/* Now change the directory to collect fork pid data */
+	dpk->dir = PROBE_POINT;
+
+	if(ret)
+		printk(KERN_ERR "Unable to find required free memory. "
+				"Trace new sample module loading aborted");
+	return ret;
+}
+
+void cleanup_module(void)
+{
+	unregister_kprobe(&kp);
+
+	/* Just a single cleanup call passing the parent dir string */
+	trace_cleanup_all(SAMPLE_PARENT_DIR);
+}
+MODULE_LICENSE("GPL");
Index: linux-2.6.25-rc8-mm1/samples/trace/Makefile
===================================================================
--- linux-2.6.25-rc8-mm1.orig/samples/trace/Makefile
+++ linux-2.6.25-rc8-mm1/samples/trace/Makefile
@@ -1,4 +1,4 @@
 # builds the trace example kernel modules;
 # then to use (as root):  insmod <fork_trace.ko>
 
-obj-$(CONFIG_SAMPLE_TRACE) := fork_trace.o
+obj-$(CONFIG_SAMPLE_TRACE) := fork_trace.o fork_new_trace.o
Index: linux-2.6.25-rc8-mm1/Documentation/trace.txt
===================================================================
--- linux-2.6.25-rc8-mm1.orig/Documentation/trace.txt
+++ linux-2.6.25-rc8-mm1/Documentation/trace.txt
@@ -150,6 +150,27 @@ The steps a kernel data provider takes t
 5) Destroy the trace channel and underlying relay channel -
    trace_cleanup().
 
+Alternatively the user may choose to make use of two new interfaces --
+debugfs_printk() and debugfs_dump() -- to setup trace interface and
+trace_cleanup_all() to tear-down the same.
+
+Steps to use:
+1) Create and populate an instance of debugfs_printk_data structure. The fields
+   parent_dir and dir are mandatory. The fields buf_size, sub_buf_size and flags
+   are optional and will take default values if not populated. The field
+   'exists' is for the trace infrastructure to use.
+2) Default values for buf_size, sub_buf_size and flags are 4096, 40 and
+   TRACE_FLIGHT_CHANNEL respectively.
+3) Use debugfs_dump() to output binary data which may be acted upon by a
+   high-level program (say dumping a structure). debugfs_printk() can be used
+   for string output. Pass a pointer to the instance of debugfs_printk_data
+   structure to these functions along with other parameters. The output from
+   these functions can be found at
+   <debugfs_mount>/<parent_dir>/<dir>/trace<0..n>.
+4) trace_cleanup_all() for a given parent directory will cleanup and remove all
+   trace directories created under the specified directory.
+5) Sample code for the same can be found in samples/trace/fork_new_trace.c
+
 Kernel Configuration
 --------------------
 To use trace, configure your kernel with CONFIG_TRACE=y. Trace depends on

Re: [RFC Patch 1/1] debugfs_printk and debugfs_dump interface

[Michael Ellerman]

[-- Attachment #1: Type: text/plain, Size: 1265 bytes --]

On Fri, 2008-04-25 at 13:49 +0530, K. Prasad wrote:
> On Fri, Apr 25, 2008 at 01:12:00PM +0530, K. Prasad wrote:
> > Please find the new patch below.
> > > 
> Let the email slip through a little early. Please find the revised
> patch below.
> 
> Thanks,
> K.Prasad
> 
> This patch introduces two new interfaces called debugfs_printk and 
> debugfs_dump which can be used to print to the debugfs mount directly.
> It uses the 'trace' infrastructure underneath and is a patch over it.
> A sample file is also created to demonstrate its ease of use.

I still think debugfs_printk() is not the right name, as it is not part
of the existing family of debugfs_* routines.

>  Documentation/trace.txt        |   21 ++++
>  include/linux/trace.h          |   55 +++++++++++
>  lib/trace.c                    |  202 +++++++++++++++++++++++++++++++++++++++--
>  samples/trace/Makefile         |    2 
>  samples/trace/fork_new_trace.c |   97 +++++++++++++++++++

And it's not in debugfs.h

cheers

-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 189 bytes --]

Re: [RFC Patch 1/1] debugfs_printk and debugfs_dump interface

[K. Prasad]

On Mon, Apr 28, 2008 at 10:50:51AM +1000, Michael Ellerman wrote:
> On Fri, 2008-04-25 at 13:49 +0530, K. Prasad wrote:
> > On Fri, Apr 25, 2008 at 01:12:00PM +0530, K. Prasad wrote:
> > > Please find the new patch below.
> > > > 
> > Let the email slip through a little early. Please find the revised
> > patch below.
> > 
> > Thanks,
> > K.Prasad
> > 
> > This patch introduces two new interfaces called debugfs_printk and 
> > debugfs_dump which can be used to print to the debugfs mount directly.
> > It uses the 'trace' infrastructure underneath and is a patch over it.
> > A sample file is also created to demonstrate its ease of use.
> 
> I still think debugfs_printk() is not the right name, as it is not part
> of the existing family of debugfs_* routines.
Whether to call it trace_printk() and trace_dump() is a suggestion I
would like to ask David Wilder (and others). Let me know if you think
there are better names.

Thanks,
K.Prasad

Re: [RFC Patch 1/1] debugfs_printk and debugfs_dump interface

[Michael Ellerman]

[-- Attachment #1: Type: text/plain, Size: 1467 bytes --]

On Mon, 2008-04-28 at 10:18 +0530, K. Prasad wrote:
> On Mon, Apr 28, 2008 at 10:50:51AM +1000, Michael Ellerman wrote:
> > On Fri, 2008-04-25 at 13:49 +0530, K. Prasad wrote:
> > > On Fri, Apr 25, 2008 at 01:12:00PM +0530, K. Prasad wrote:
> > > > Please find the new patch below.
> > > > > 
> > > Let the email slip through a little early. Please find the revised
> > > patch below.
> > > 
> > > Thanks,
> > > K.Prasad
> > > 
> > > This patch introduces two new interfaces called debugfs_printk and 
> > > debugfs_dump which can be used to print to the debugfs mount directly.
> > > It uses the 'trace' infrastructure underneath and is a patch over it.
> > > A sample file is also created to demonstrate its ease of use.
> > 
> > I still think debugfs_printk() is not the right name, as it is not part
> > of the existing family of debugfs_* routines.

> Whether to call it trace_printk() and trace_dump() is a suggestion I
> would like to ask David Wilder (and others). Let me know if you think
> there are better names.

That would be my pick, given that it's using the trace infrastructure
and it's defined in trace.h, implemented in trace.c, and documented in
trace.txt :)

cheers

-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 189 bytes --]