tracing/ftrace: replace none tracer by nop tracer

Replace "none" tracer by the recently created "nop" tracer.
Both are pretty similar except that nop accepts TRACE_PRINT
or TRACE_SPECIAL entries.

And as a consequence, changing the size of the ring buffer now
requires that tracing has already been disabled.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Steven Noonan <steven@uplinklabs.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 12 insertions, 46 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index eee1fd964898..f2ef72fa3f17 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -142,24 +142,6 @@ static DECLARE_WAIT_QUEUE_HEAD(trace_wait);
 /* trace_flags holds iter_ctrl options */
 unsigned long trace_flags = TRACE_ITER_PRINT_PARENT;
 
-static notrace void no_trace_init(struct trace_array *tr)
-{
-        int cpu;
-
-        ftrace_function_enabled = 0;
-        if(tr->ctrl)
-                for_each_online_cpu(cpu)
-                        tracing_reset(tr->data[cpu]);
-        tracer_enabled = 0;
-}
-
-/* dummy trace to disable tracing */
-static struct tracer no_tracer __read_mostly = {
-        .name           = "none",
-        .init           = no_trace_init
-};
-
-
 /**
  * trace_wake_up - wake up tasks waiting for trace input
  *
@@ -962,7 +944,7 @@ ftrace_special(unsigned long arg1, unsigned long arg2, unsigned long arg3)
         long disabled;
         int cpu;
 
-        if (tracing_disabled || current_trace == &no_tracer || !tr->ctrl)
+        if (tracing_disabled || !tr->ctrl)
                 return;
 
         local_irq_save(flags);
@@ -2795,6 +2777,7 @@ tracing_entries_write(struct file *filp, const char __user *ubuf,
         unsigned long val;
         char buf[64];
         int i, ret;
+        struct trace_array *tr = filp->private_data;
 
         if (cnt >= sizeof(buf))
                 return -EINVAL;
@@ -2814,9 +2797,9 @@ tracing_entries_write(struct file *filp, const char __user *ubuf,
 
         mutex_lock(&trace_types_lock);
 
-        if (current_trace != &no_tracer) {
+        if (tr->ctrl) {
                 cnt = -EBUSY;
-                pr_info("ftrace: set current_tracer to none"
+                pr_info("ftrace: please disable tracing"
                         " before modifying buffer size\n");
                 goto out;
         }
@@ -2879,20 +2862,6 @@ tracing_entries_write(struct file *filp, const char __user *ubuf,
         return cnt;
 }
 
-static int tracing_open_mark(struct inode *inode, struct file *filp)
-{
-        int ret;
-
-        ret = tracing_open_generic(inode, filp);
-        if (ret)
-                return ret;
-
-        if (current_trace == &no_tracer)
-                return -ENODEV;
-
-        return 0;
-}
-
 static int mark_printk(const char *fmt, ...)
 {
         int ret;
@@ -2911,7 +2880,7 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
         char *end;
         struct trace_array *tr = &global_trace;
 
-        if (current_trace == &no_tracer || !tr->ctrl || tracing_disabled)
+        if (!tr->ctrl || tracing_disabled)
                 return -EINVAL;
 
         if (cnt > TRACE_BUF_SIZE)
@@ -2971,7 +2940,7 @@ static struct file_operations tracing_entries_fops = {
 };
 
 static struct file_operations tracing_mark_fops = {
-        .open           = tracing_open_mark,
+        .open           = tracing_open_generic,
         .write          = tracing_mark_write,
 };
 
@@ -3123,7 +3092,7 @@ int trace_vprintk(unsigned long ip, const char *fmt, va_list args)
         long disabled;
         int cpu, len = 0, write, written = 0;
 
-        if (current_trace == &no_tracer || !tr->ctrl || tracing_disabled)
+        if (!tr->ctrl || tracing_disabled)
                 return 0;
 
         local_irq_save(flags);
@@ -3539,8 +3508,8 @@ __init static int tracer_alloc_buffers(void)
 
         trace_init_cmdlines();
 
-        register_tracer(&no_tracer);
-        current_trace = &no_tracer;
+        register_tracer(&nop_trace);
+        current_trace = &nop_trace;
 
         /* All seems OK, enable tracing */
         global_trace.ctrl = tracer_enabled;
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index c8c687088b4d..cb2c3fb7dd54 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -369,4 +369,6 @@ enum trace_iterator_flags {
         TRACE_ITER_PRINTK               = 0x400,
 };
 
+extern struct tracer nop_trace;
+
 #endif /* _LINUX_KERNEL_TRACE_H */
diff --git a/kernel/trace/trace_nop.c b/kernel/trace/trace_nop.c
index 9fb02c17ad0c..16c9ba060bab 100644
--- a/kernel/trace/trace_nop.c
+++ b/kernel/trace/trace_nop.c
@@ -51,7 +51,7 @@ static void nop_trace_ctrl_update(struct trace_array *tr)
                 stop_nop_trace(tr);
 }
 
-static struct tracer nop_trace __read_mostly =
+struct tracer nop_trace __read_mostly =
 {
         .name           = "nop",
         .init           = nop_trace_init,
@@ -62,8 +62,3 @@ static struct tracer nop_trace __read_mostly =
 #endif
 };
 
-__init static int init_nop_trace(void)
-{
-        return register_tracer(&nop_trace);
-}
-device_initcall(init_nop_trace);