tracing: give easy way to clear trace buffer

[GitHub/mt8127/android_kernel_alcatel_ttab.git] / kernel / trace / trace.c

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a2d13e8c8fd880da0a91b179c2da6894e263cc0c..8d981ababc453240b9890a56c4f8d98bdda19631 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1941,9 +1941,14 @@ int tracing_open_generic(struct inode *inode, struct file *filp)
 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 @@ static int tracing_open(struct inode *inode, struct file *file)
        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 @@ static int show_traces_open(struct inode *inode, struct file *file)
        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 @@ static void tracing_init_debugfs_percpu(long cpu)
                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 @@ static __init int tracer_init_debugfs(void)
        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");