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SubjectRe: [PATCH 1/7] tracing: give easy way to clear trace buffer
On Thu, Mar 19, 2009 at 04:01:23PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@redhat.com>
>
> 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>
> ---
> kernel/trace/trace.c | 41 +++++++++++++++++++++++++++++++++--------
> 1 files changed, 33 insertions(+), 8 deletions(-)
>
> 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 @@ 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;
> +}


Is this one necessary?
I guess debugfs or vfs layers already provide a stub for write. No?

Anyway, that's a small detail for this good patch idea.

Frederic.


> 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");
> --
> 1.6.2
>
> --
> --
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