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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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