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Message-Id: <1204065533.26964.18.camel@lc4eb748232119.ibm.com>
Date: Tue, 26 Feb 2008 14:38:52 -0800
From: "David J. Wilder" <dwilder@...ibm.com>
To: linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Cc: systemtap@...rceware.org, prasadav@...ibm.com, hch@...radead.org
Subject: [patch 3/3] Trace sample
Trace example - Adds the trace example to samples/
Signed-off-by: David Wilder <dwilder@...ibm.com>
---
samples/Kconfig | 6 ++
samples/Makefile | 2 +-
samples/trace/Makefile | 4 +
samples/trace/fork_trace.c | 132 ++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 143 insertions(+), 1 deletions(-)
diff --git a/samples/Kconfig b/samples/Kconfig
index 74d97cc..980c574 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -22,5 +22,11 @@ config SAMPLE_KOBJECT
If in doubt, say "N" here.
+config SAMPLE_TRACE
+ tristate "Build trace example -- loadable modules only"
+ depends on TRACE && KPROBES && m
+ help
+ This builds a trace example module.
+
endif # SAMPLES
diff --git a/samples/Makefile b/samples/Makefile
index 8652d0f..47db118 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -1,3 +1,3 @@
# Makefile for Linux samples code
-obj-$(CONFIG_SAMPLES) += markers/ kobject/
+obj-$(CONFIG_SAMPLES) += markers/ kobject/ trace/
diff --git a/samples/trace/Makefile b/samples/trace/Makefile
new file mode 100644
index 0000000..e33f276
--- /dev/null
+++ b/samples/trace/Makefile
@@ -0,0 +1,4 @@
+# builds the trace example kernel modules;
+# then to use (as root): insmod <fork_trace.ko>
+
+obj-$(CONFIG_SAMPLE_TRACE) := fork_trace.o
diff --git a/samples/trace/fork_trace.c b/samples/trace/fork_trace.c
new file mode 100644
index 0000000..71c04c7
--- /dev/null
+++ b/samples/trace/fork_trace.c
@@ -0,0 +1,132 @@
+/*
+ * An example of using trace in a kprobes module
+ *
+ * Copyright (C) 2007 IBM Inc.
+ *
+ * David Wilder <dwilder@...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 USE_GLOBAL_BUFFERS 1
+#define USE_FLIGHT 1
+
+#define PROBE_POINT "do_fork"
+
+static struct kprobe kp;
+static struct trace_info *kprobes_trace;
+
+#ifdef USE_GLOBAL_BUFFERS
+static DEFINE_SPINLOCK(trace_lock);
+#endif
+
+/*
+ * Send formatted trace data to trace channel.
+ * @note Preemption must be disabled to use this.
+ */
+static void trace_printf(struct trace_info *trace, const char *format, ...)
+{
+ va_list ap, aq;
+ char *record;
+ unsigned long flags;
+ int len;
+
+ if (!trace)
+ return;
+
+#ifdef USE_GLOBAL_BUFFERS
+ spin_lock_irqsave(&trace_lock, flags);
+#endif
+ if (trace_running(trace)) {
+ va_start(ap, format);
+ va_copy(aq, ap);
+ len = vsnprintf(NULL, 0, format, aq);
+ va_end(aq);
+ record = relay_reserve(trace->rchan, ++len);
+ if (record)
+ vsnprintf(record, len, format, ap);
+ va_end(ap);
+ }
+#ifdef USE_GLOBAL_BUFFERS
+ spin_unlock_irqrestore(&trace_lock, flags);
+#endif
+}
+
+static int handler_pre(struct kprobe *p, struct pt_regs *regs)
+{
+ rcu_read_lock();
+ trace_printf(kprobes_trace, "%d\n", current->pid);
+ rcu_read_unlock();
+ return 0;
+}
+
+int init_module(void)
+{
+ int ret;
+ u32 flags = 0;
+
+#ifdef USE_GLOBAL_BUFFERS
+ flags |= TRACE_GLOBAL_CHANNEL;
+#endif
+
+#ifdef USE_FLIGHT
+ flags |= TRACE_FLIGHT_CHANNEL;
+#endif
+
+ /* setup the trace */
+ kprobes_trace = trace_setup("trace_example", PROBE_POINT,
+ 1024, 8, flags);
+ if (IS_ERR(kprobes_trace))
+ return PTR_ERR(kprobes_trace);
+
+ trace_start(kprobes_trace);
+
+ /* 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;
+ }
+ return 0;
+}
+
+void cleanup_module(void)
+{
+ unregister_kprobe(&kp);
+ trace_stop(kprobes_trace);
+ trace_cleanup(kprobes_trace);
+}
+MODULE_LICENSE("GPL");
--
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