ring-buffer: buffer record on/off switch

Impact: enable/disable ring buffer recording API added Several kernel developers have requested that there be a way to stop recording into the ring buffers with a simple switch that can also be enabled from userspace. This patch addes a new kernel API to the ring buffers called: tracing_on() tracing_off() When tracing_off() is called, all ring buffers will not be able to record into their buffers. tracing_on() will enable the ring buffers again. These two act like an on/off switch. That is, there is no counting of the number of times tracing_off or tracing_on has been called. A new file is added to the debugfs/tracing directory called tracing_on This allows for userspace applications to also flip the switch. echo 0 > debugfs/tracing/tracing_on disables the tracing. echo 1 > /debugfs/tracing/tracing_on enables it. Note, this does not disable or enable any tracers. It only sets or clears a flag that needs to be set in order for the ring buffers to write to their buffers. It is a global flag, and affects all ring buffers. The buffers start out with tracing_on enabled. There are now three flags that control recording into the buffers: tracing_on: which affects all ring buffer tracers. buffer->record_disabled: which affects an allocated buffer, which may be set if an anomaly is detected, and tracing is disabled. cpu_buffer->record_disabled: which is set by tracing_stop() or if an anomaly is detected. tracing_start can not reenable this if an anomaly occurred. The userspace debugfs/tracing/tracing_enabled is implemented with tracing_stop() but the user space code can not enable it if the kernel called tracing_stop(). Userspace can enable the tracing_on even if the kernel disabled it. It is just a switch used to stop tracing if a condition was hit. tracing_on is not for protecting critical areas in the kernel nor is it for stopping tracing if an anomaly occurred. This is because userspace can reenable it at any time. Side effect: With this patch, I discovered a dead variable in ftrace.c called tracing_on. This patch removes it. Signed-off-by: Steven Rostedt <srostedt@redhat.com>

ring-buffer: buffer record on/off switch
Impact: enable/disable ring buffer recording API added Several kernel developers have requested that there be a way to stop recording into the ring buffers with a simple switch that can also be enabled from userspace. This patch addes a new kernel API to the ring buffers called: tracing_on() tracing_off() When tracing_off() is called, all ring buffers will not be able to record into their buffers. tracing_on() will enable the ring buffers again. These two act like an on/off switch. That is, there is no counting of the number of times tracing_off or tracing_on has been called. A new file is added to the debugfs/tracing directory called tracing_on This allows for userspace applications to also flip the switch. echo 0 > debugfs/tracing/tracing_on disables the tracing. echo 1 > /debugfs/tracing/tracing_on enables it. Note, this does not disable or enable any tracers. It only sets or clears a flag that needs to be set in order for the ring buffers to write to their buffers. It is a global flag, and affects all ring buffers. The buffers start out with tracing_on enabled. There are now three flags that control recording into the buffers: tracing_on: which affects all ring buffer tracers. buffer->record_disabled: which affects an allocated buffer, which may be set if an anomaly is detected, and tracing is disabled. cpu_buffer->record_disabled: which is set by tracing_stop() or if an anomaly is detected. tracing_start can not reenable this if an anomaly occurred. The userspace debugfs/tracing/tracing_enabled is implemented with tracing_stop() but the user space code can not enable it if the kernel called tracing_stop(). Userspace can enable the tracing_on even if the kernel disabled it. It is just a switch used to stop tracing if a condition was hit. tracing_on is not for protecting critical areas in the kernel nor is it for stopping tracing if an anomaly occurred. This is because userspace can reenable it at any time. Side effect: With this patch, I discovered a dead variable in ftrace.c called tracing_on. This patch removes it. Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Steven Rostedt
1 parent 4143c5cb36
Showing 3 changed files with 106 additions and 6 deletions Side-by-side Diff
include/linux/ring_buffer.h
kernel/trace/ftrace.c
kernel/trace/ring_buffer.c
@@ -120,6 +120,9 @@
 u64 ring_buffer_time_stamp(int cpu);
 void ring_buffer_normalize_time_stamp(int cpu, u64 *ts);
  
+void tracing_on(void);
+void tracing_off(void);
+
 enum ring_buffer_flags {
 	RB_FL_OVERWRITE		= 1 << 0,
 };
@@ -185,7 +185,6 @@
 };
  
 static int ftrace_filtered;
-static int tracing_on;
  
 static LIST_HEAD(ftrace_new_addrs);
  
  
  
@@ -506,13 +505,10 @@
 {
 	int *command = data;
  
-	if (*command & FTRACE_ENABLE_CALLS) {
+	if (*command & FTRACE_ENABLE_CALLS)
 		ftrace_replace_code(1);
-		tracing_on = 1;
-	} else if (*command & FTRACE_DISABLE_CALLS) {
+	else if (*command & FTRACE_DISABLE_CALLS)
 		ftrace_replace_code(0);
-		tracing_on = 0;
-	}
  
 	if (*command & FTRACE_UPDATE_TRACE_FUNC)
 		ftrace_update_ftrace_func(ftrace_trace_function);
@@ -16,6 +16,35 @@
 #include <linux/list.h>
 #include <linux/fs.h>
  
+#include "trace.h"
+
+/* Global flag to disable all recording to ring buffers */
+static int ring_buffers_off __read_mostly;
+
+/**
+ * tracing_on - enable all tracing buffers
+ *
+ * This function enables all tracing buffers that may have been
+ * disabled with tracing_off.
+ */
+void tracing_on(void)
+{
+	ring_buffers_off = 0;
+}
+
+/**
+ * tracing_off - turn off all tracing buffers
+ *
+ * This function stops all tracing buffers from recording data.
+ * It does not disable any overhead the tracers themselves may
+ * be causing. This function simply causes all recording to
+ * the ring buffers to fail.
+ */
+void tracing_off(void)
+{
+	ring_buffers_off = 1;
+}
+
 /* Up this if you want to test the TIME_EXTENTS and normalization */
 #define DEBUG_SHIFT 0
  
@@ -1133,6 +1162,9 @@
 	struct ring_buffer_event *event;
 	int cpu, resched;
  
+	if (ring_buffers_off)
+		return NULL;
+
 	if (atomic_read(&buffer->record_disabled))
 		return NULL;
  
@@ -1249,6 +1281,9 @@
 	int ret = -EBUSY;
 	int cpu, resched;
  
+	if (ring_buffers_off)
+		return -EBUSY;
+
 	if (atomic_read(&buffer->record_disabled))
 		return -EBUSY;
  
@@ -2069,4 +2104,71 @@
  
 	return 0;
 }
+
+static ssize_t
+rb_simple_read(struct file *filp, char __user *ubuf,
+	       size_t cnt, loff_t *ppos)
+{
+	int *p = filp->private_data;
+	char buf[64];
+	int r;
+
+	/* !ring_buffers_off == tracing_on */
+	r = sprintf(buf, "%d\n", !*p);
+
+	return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
+}
+
+static ssize_t
+rb_simple_write(struct file *filp, const char __user *ubuf,
+		size_t cnt, loff_t *ppos)
+{
+	int *p = filp->private_data;
+	char buf[64];
+	long val;
+	int ret;
+
+	if (cnt >= sizeof(buf))
+		return -EINVAL;
+
+	if (copy_from_user(&buf, ubuf, cnt))
+		return -EFAULT;
+
+	buf[cnt] = 0;
+
+	ret = strict_strtoul(buf, 10, &val);
+	if (ret < 0)
+		return ret;
+
+	/* !ring_buffers_off == tracing_on */
+	*p = !val;
+
+	(*ppos)++;
+
+	return cnt;
+}
+
+static struct file_operations rb_simple_fops = {
+	.open		= tracing_open_generic,
+	.read		= rb_simple_read,
+	.write		= rb_simple_write,
+};
+
+
+static __init int rb_init_debugfs(void)
+{
+	struct dentry *d_tracer;
+	struct dentry *entry;
+
+	d_tracer = tracing_init_dentry();
+
+	entry = debugfs_create_file("tracing_on", 0644, d_tracer,
+				    &ring_buffers_off, &rb_simple_fops);
+	if (!entry)
+		pr_warning("Could not create debugfs 'tracing_on' entry\n");
+
+	return 0;
+}
+
+fs_initcall(rb_init_debugfs);
...	...	@@ -120,6 +120,9 @@
120	120	u64 ring_buffer_time_stamp(int cpu);
121	121	void ring_buffer_normalize_time_stamp(int cpu, u64 *ts);
122	122
	123	+void tracing_on(void);
	124	+void tracing_off(void);
	125	+
123	126	enum ring_buffer_flags {
124	127	RB_FL_OVERWRITE = 1 << 0,
125	128	};
...	...	@@ -185,7 +185,6 @@
185	185	};
186	186
187	187	static int ftrace_filtered;
188		-static int tracing_on;
189	188
190	189	static LIST_HEAD(ftrace_new_addrs);
191	190
192	191
193	192
...	...	@@ -506,13 +505,10 @@
506	505	{
507	506	int *command = data;
508	507
509		- if (*command & FTRACE_ENABLE_CALLS) {
	508	+ if (*command & FTRACE_ENABLE_CALLS)
510	509	ftrace_replace_code(1);
511		- tracing_on = 1;
512		- } else if (*command & FTRACE_DISABLE_CALLS) {
	510	+ else if (*command & FTRACE_DISABLE_CALLS)
513	511	ftrace_replace_code(0);
514		- tracing_on = 0;
515		- }
516	512
517	513	if (*command & FTRACE_UPDATE_TRACE_FUNC)
518	514	ftrace_update_ftrace_func(ftrace_trace_function);
...	...	@@ -16,6 +16,35 @@
16	16	#include <linux/list.h>
17	17	#include <linux/fs.h>
18	18
	19	+#include "trace.h"
	20	+
	21	+/* Global flag to disable all recording to ring buffers */
	22	+static int ring_buffers_off __read_mostly;
	23	+
	24	+/**
	25	+ * tracing_on - enable all tracing buffers
	26	+ *
	27	+ * This function enables all tracing buffers that may have been
	28	+ * disabled with tracing_off.
	29	+ */
	30	+void tracing_on(void)
	31	+{
	32	+ ring_buffers_off = 0;
	33	+}
	34	+
	35	+/**
	36	+ * tracing_off - turn off all tracing buffers
	37	+ *
	38	+ * This function stops all tracing buffers from recording data.
	39	+ * It does not disable any overhead the tracers themselves may
	40	+ * be causing. This function simply causes all recording to
	41	+ * the ring buffers to fail.
	42	+ */
	43	+void tracing_off(void)
	44	+{
	45	+ ring_buffers_off = 1;
	46	+}
	47	+
19	48	/* Up this if you want to test the TIME_EXTENTS and normalization */
20	49	#define DEBUG_SHIFT 0
21	50
...	...	@@ -1133,6 +1162,9 @@
1133	1162	struct ring_buffer_event *event;
1134	1163	int cpu, resched;
1135	1164
	1165	+ if (ring_buffers_off)
	1166	+ return NULL;
	1167	+
1136	1168	if (atomic_read(&buffer->record_disabled))
1137	1169	return NULL;
1138	1170
...	...	@@ -1249,6 +1281,9 @@
1249	1281	int ret = -EBUSY;
1250	1282	int cpu, resched;
1251	1283
	1284	+ if (ring_buffers_off)
	1285	+ return -EBUSY;
	1286	+
1252	1287	if (atomic_read(&buffer->record_disabled))
1253	1288	return -EBUSY;
1254	1289
...	...	@@ -2069,4 +2104,71 @@
2069	2104
2070	2105	return 0;
2071	2106	}
	2107	+
	2108	+static ssize_t
	2109	+rb_simple_read(struct file filp, char __user ubuf,
	2110	+ size_t cnt, loff_t *ppos)
	2111	+{
	2112	+ int *p = filp->private_data;
	2113	+ char buf[64];
	2114	+ int r;
	2115	+
	2116	+ /* !ring_buffers_off == tracing_on */
	2117	+ r = sprintf(buf, "%d\n", !*p);
	2118	+
	2119	+ return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
	2120	+}
	2121	+
	2122	+static ssize_t
	2123	+rb_simple_write(struct file filp, const char __user ubuf,
	2124	+ size_t cnt, loff_t *ppos)
	2125	+{
	2126	+ int *p = filp->private_data;
	2127	+ char buf[64];
	2128	+ long val;
	2129	+ int ret;
	2130	+
	2131	+ if (cnt >= sizeof(buf))
	2132	+ return -EINVAL;
	2133	+
	2134	+ if (copy_from_user(&buf, ubuf, cnt))
	2135	+ return -EFAULT;
	2136	+
	2137	+ buf[cnt] = 0;
	2138	+
	2139	+ ret = strict_strtoul(buf, 10, &val);
	2140	+ if (ret < 0)
	2141	+ return ret;
	2142	+
	2143	+ /* !ring_buffers_off == tracing_on */
	2144	+ *p = !val;
	2145	+
	2146	+ (*ppos)++;
	2147	+
	2148	+ return cnt;
	2149	+}
	2150	+
	2151	+static struct file_operations rb_simple_fops = {
	2152	+ .open = tracing_open_generic,
	2153	+ .read = rb_simple_read,
	2154	+ .write = rb_simple_write,
	2155	+};
	2156	+
	2157	+
	2158	+static __init int rb_init_debugfs(void)
	2159	+{
	2160	+ struct dentry *d_tracer;
	2161	+ struct dentry *entry;
	2162	+
	2163	+ d_tracer = tracing_init_dentry();
	2164	+
	2165	+ entry = debugfs_create_file("tracing_on", 0644, d_tracer,
	2166	+ &ring_buffers_off, &rb_simple_fops);
	2167	+ if (!entry)
	2168	+ pr_warning("Could not create debugfs 'tracing_on' entry\n");
	2169	+
	2170	+ return 0;
	2171	+}
	2172	+
	2173	+fs_initcall(rb_init_debugfs);