tracing: give easy way to clear trace buffer
There is currently no easy way to clear the trace buffer. Currently
the only way is to change the current tracer.
This patch lets the user clear the trace buffer by simply writing
into the trace files.
echo > /debug/tracing/trace
or to clear a single cpu (i.e. for CPU 1):
echo > /debug/tracing/per_cpu/cpu1/trace
Requested-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a2d13e8..8d981ab 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1941,9 +1941,14 @@
static int tracing_release(struct inode *inode, struct file *file)
{
struct seq_file *m = (struct seq_file *)file->private_data;
- struct trace_iterator *iter = m->private;
+ struct trace_iterator *iter;
int cpu;
+ if (!(file->f_mode & FMODE_READ))
+ return 0;
+
+ iter = m->private;
+
mutex_lock(&trace_types_lock);
for_each_tracing_cpu(cpu) {
if (iter->buffer_iter[cpu])
@@ -1969,12 +1974,24 @@
struct trace_iterator *iter;
int ret = 0;
- iter = __tracing_open(inode, file);
- if (IS_ERR(iter))
- ret = PTR_ERR(iter);
- else if (trace_flags & TRACE_ITER_LATENCY_FMT)
- iter->iter_flags |= TRACE_FILE_LAT_FMT;
+ /* If this file was open for write, then erase contents */
+ if ((file->f_mode & FMODE_WRITE) &&
+ !(file->f_flags & O_APPEND)) {
+ long cpu = (long) inode->i_private;
+ if (cpu == TRACE_PIPE_ALL_CPU)
+ tracing_reset_online_cpus(&global_trace);
+ else
+ tracing_reset(&global_trace, cpu);
+ }
+
+ if (file->f_mode & FMODE_READ) {
+ iter = __tracing_open(inode, file);
+ if (IS_ERR(iter))
+ ret = PTR_ERR(iter);
+ else if (trace_flags & TRACE_ITER_LATENCY_FMT)
+ iter->iter_flags |= TRACE_FILE_LAT_FMT;
+ }
return ret;
}
@@ -2049,9 +2066,17 @@
return ret;
}
+static ssize_t
+tracing_write_stub(struct file *filp, const char __user *ubuf,
+ size_t count, loff_t *ppos)
+{
+ return count;
+}
+
static const struct file_operations tracing_fops = {
.open = tracing_open,
.read = seq_read,
+ .write = tracing_write_stub,
.llseek = seq_lseek,
.release = tracing_release,
};
@@ -3576,7 +3601,7 @@
pr_warning("Could not create debugfs 'trace_pipe' entry\n");
/* per cpu trace */
- entry = debugfs_create_file("trace", 0444, d_cpu,
+ entry = debugfs_create_file("trace", 0644, d_cpu,
(void *) cpu, &tracing_fops);
if (!entry)
pr_warning("Could not create debugfs 'trace' entry\n");
@@ -3890,7 +3915,7 @@
if (!entry)
pr_warning("Could not create debugfs 'tracing_cpumask' entry\n");
- entry = debugfs_create_file("trace", 0444, d_tracer,
+ entry = debugfs_create_file("trace", 0644, d_tracer,
(void *) TRACE_PIPE_ALL_CPU, &tracing_fops);
if (!entry)
pr_warning("Could not create debugfs 'trace' entry\n");