Re: [PATCH 01/15] tracing: Add a 'buffer_overwrite' debugfs file

[David Sharp]

On Fri, Dec 3, 2010 at 5:57 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> On Fri, 2010-12-03 at 16:13 -0800, David Sharp wrote:
>> From: Jiaying Zhang <jiayingz@xxxxxxxxxx>
>>
>> Add a "buffer_overwrite" debugfs file for ftrace to control whether the buffer
>
> Instead of adding a new file, make this another "trace_option".

To do this, I had to add a special case to set_tracer_flags() to call
ring_buffer_change_overwrite. It also means adding something not
iterator-related to trace_iterator_flags. Although, maybe it's just
the name of the enum and value prefix that should change.

I'll send the new patch to you separately today.

>
> Thanks,
>
> -- Steve
>
>
>> should be overwritten on overflow or not. The default remains to overwrite old
>> events when the buffer is full. This patch adds the option to instead discard
>> newest events when the buffer is full. This is useful to get a snapshot of
>> traces just after enabling traces. Dropping the current event is also a simpler
>> code path.
>>
>> Signed-off-by: David Sharp <dhsharp@xxxxxxxxxx>
>> ---
>> ÂDocumentation/trace/ftrace.txt | Â Â6 ++++
>> Âinclude/linux/ring_buffer.h  Â|  Â2 +
>> Âkernel/trace/ring_buffer.c   |  11 +++++++
>> Âkernel/trace/trace.c      |  59 +++++++++++++++++++++++++++++++++++++---
>> Â4 files changed, 74 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
>> index 557c1ed..9237da3 100644
>> --- a/Documentation/trace/ftrace.txt
>> +++ b/Documentation/trace/ftrace.txt
>> @@ -138,6 +138,12 @@ of ftrace. Here is a list of some of the key files:
>> Â Â Â This can only be updated when the current_tracer
>> Â Â Â is set to "nop".
>>
>> + Âbuffer_overwrite:
>> +
>> + Â Â This controls what happens when the trace buffer is full.
>> + Â Â If "1" (default), the oldest events are discarded and
>> + Â Â overwritten. If "0", then the newest events are discarded.
>> +
>> Â Âtracing_cpumask:
>>
>> Â Â Â This is a mask that lets the user only trace
>> diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
>> index 8d3a248..ab38ac8 100644
>> --- a/include/linux/ring_buffer.h
>> +++ b/include/linux/ring_buffer.h
>> @@ -100,6 +100,8 @@ void ring_buffer_free(struct ring_buffer *buffer);
>>
>> Âint ring_buffer_resize(struct ring_buffer *buffer, unsigned long size);
>>
>> +void ring_buffer_change_overwrite(struct ring_buffer *buffer, int val);
>> +
>> Âstruct ring_buffer_event *ring_buffer_lock_reserve(struct ring_buffer *buffer,
>> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Âunsigned long length);
>> Âint ring_buffer_unlock_commit(struct ring_buffer *buffer,
>> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
>> index 9ed509a..3207147 100644
>> --- a/kernel/trace/ring_buffer.c
>> +++ b/kernel/trace/ring_buffer.c
>> @@ -1429,6 +1429,17 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
>> Â}
>> ÂEXPORT_SYMBOL_GPL(ring_buffer_resize);
>>
>> +void ring_buffer_change_overwrite(struct ring_buffer *buffer, int val)
>> +{
>> + Â Â mutex_lock(&buffer->mutex);
>> + Â Â if (val)
>> + Â Â Â Â Â Â buffer->flags |= RB_FL_OVERWRITE;
>> + Â Â else
>> + Â Â Â Â Â Â buffer->flags &= ~RB_FL_OVERWRITE;
>> + Â Â mutex_unlock(&buffer->mutex);
>> +}
>> +EXPORT_SYMBOL_GPL(ring_buffer_change_overwrite);
>> +
>> Âstatic inline void *
>> Â__rb_data_page_index(struct buffer_data_page *bpage, unsigned index)
>> Â{
>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
>> index c380612..ed5c14f 100644
>> --- a/kernel/trace/trace.c
>> +++ b/kernel/trace/trace.c
>> @@ -41,8 +41,6 @@
>> Â#include "trace.h"
>> Â#include "trace_output.h"
>>
>> -#define TRACE_BUFFER_FLAGS Â (RB_FL_OVERWRITE)
>> -
>> Â/*
>> Â * On boot up, the ring buffer is set to the minimum size, so that
>> Â * we do not waste memory on systems that are not using tracing.
>> @@ -241,6 +239,9 @@ int tracing_is_enabled(void)
>>
>> Âstatic unsigned long     trace_buf_size = TRACE_BUF_SIZE_DEFAULT;
>>
>> +/* whether the trace buffer should be overwritten on overflow or not. */
>> +static enum ring_buffer_flags Âtrace_buffer_flags = RB_FL_OVERWRITE;
>> +
>> Â/* trace_types holds a link list of available tracers. */
>> Âstatic struct tracer     *trace_types __read_mostly;
>>
>> @@ -3466,6 +3467,47 @@ tracing_entries_write(struct file *filp, const char __user *ubuf,
>> Â Â Â return cnt;
>> Â}
>>
>> +static ssize_t
>> +tracing_overwrite_read(struct file *filp, char __user *ubuf,
>> + Â Â Â Â Â Â Â Â Âsize_t cnt, loff_t *ppos)
>> +{
>> + Â Â char buf[64];
>> + Â Â int r;
>> + Â Â r = snprintf(buf, 64, "%u\n", trace_buffer_flags);
>> + Â Â return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
>> +}
>> +
>> +static ssize_t
>> +tracing_overwrite_write(struct file *filp, const char __user *ubuf,
>> + Â Â Â Â Â Â Â Â Â size_t cnt, loff_t *ppos)
>> +{
>> + Â Â unsigned long val;
>> + Â Â char buf[64];
>> + Â Â int ret;
>> +
>> + Â Â if (cnt >= sizeof(buf))
>> + Â Â Â Â Â Â return -EINVAL;
>> +
>> + Â Â if (copy_from_user(&buf, ubuf, cnt))
>> + Â Â Â Â Â Â return -EFAULT;
>> +
>> + Â Â buf[cnt] = 0;
>> +
>> + Â Â ret = strict_strtoul(buf, 10, &val);
>> + Â Â if (ret < 0)
>> + Â Â Â Â Â Â return ret;
>> + Â Â *ppos += cnt;
>> +
>> + Â Â if (val != 0 && val != 1)
>> + Â Â Â Â Â Â return -EINVAL;
>> +
>> + Â Â if (trace_buffer_flags != val) {
>> + Â Â Â Â Â Â trace_buffer_flags = val;
>> + Â Â Â Â Â Â ring_buffer_change_overwrite(global_trace.buffer, val);
>> + Â Â }
>> + Â Â return cnt;
>> +}
>> +
>> Âstatic int mark_printk(const char *fmt, ...)
>> Â{
>> Â Â Â int ret;
>> @@ -3611,6 +3653,12 @@ static const struct file_operations tracing_entries_fops = {
>>    .llseek     = generic_file_llseek,
>> Â};
>>
>> +static const struct file_operations tracing_overwrite_fops = {
>> +   .open      = tracing_open_generic,
>> +   .read      = tracing_overwrite_read,
>> +   .write     Â= tracing_overwrite_write,
>> +};
>> +
>> Âstatic const struct file_operations tracing_mark_fops = {
>>    .open      = tracing_open_generic,
>>    .write     Â= tracing_mark_write,
>> @@ -4336,6 +4384,9 @@ static __init int tracer_init_debugfs(void)
>> Â Â Â trace_create_file("buffer_size_kb", 0644, d_tracer,
>> Â Â Â Â Â Â Â Â Â Â Â &global_trace, &tracing_entries_fops);
>>
>> + Â Â trace_create_file("buffer_overwrite", 0644, d_tracer,
>> + Â Â Â Â Â Â Â Â Â Â &global_trace, &tracing_overwrite_fops);
>> +
>> Â Â Â trace_create_file("trace_marker", 0220, d_tracer,
>> Â Â Â Â Â Â Â Â Â Â Â NULL, &tracing_mark_fops);
>>
>> @@ -4565,7 +4616,7 @@ __init static int tracer_alloc_buffers(void)
>>
>> Â Â Â /* TODO: make the number of buffers hot pluggable with CPUS */
>> Â Â Â global_trace.buffer = ring_buffer_alloc(ring_buf_size,
>> - Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â ÂTRACE_BUFFER_FLAGS);
>> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Âtrace_buffer_flags);
>> Â Â Â if (!global_trace.buffer) {
>> Â Â Â Â Â Â Â printk(KERN_ERR "tracer: failed to allocate ring buffer!\n");
>> Â Â Â Â Â Â Â WARN_ON(1);
>> @@ -4575,7 +4626,7 @@ __init static int tracer_alloc_buffers(void)
>>
>>
>> Â#ifdef CONFIG_TRACER_MAX_TRACE
>> - Â Â max_tr.buffer = ring_buffer_alloc(1, TRACE_BUFFER_FLAGS);
>> + Â Â max_tr.buffer = ring_buffer_alloc(1, trace_buffer_flags);
>> Â Â Â if (!max_tr.buffer) {
>> Â Â Â Â Â Â Â printk(KERN_ERR "tracer: failed to allocate max ring buffer!\n");
>> Â Â Â Â Â Â Â WARN_ON(1);
>
>
>
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