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tracing: Replace static old_tracer check of tracer name 

Currently the trace buffer read functions use a static variable
"old_tracer" for detecting if the current tracer changes. This
was suitable for a single trace file ("trace"), but to add a
snapshot feature that will use the same function for its file,
a check against a static variable is not sufficient.

To use the output functions for two different files, instead of
storing the current tracer in a static variable, as the trace
iterator descriptor contains a pointer to the original current
tracer's name, that pointer can now be used to check if the
current tracer has changed between different reads of the trace
file.

Link: http://lkml.kernel.org/r/20121226025252.3252.9276.stgit@liselsia

Signed-off-by: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Hiraku Toyooka 2012-12-26 11:52:52 +09:00 committed by Steven Rostedt
parent 5e67b51e3f
commit 2fd196ec1e
1 changed files with 9 additions and 13 deletions
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22
kernel/trace/trace.c
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@ -1948,18 +1948,20 @@ void tracing_iter_reset(struct trace_iterator *iter, int cpu)
static void *s_start(struct seq_file *m, loff_t *pos)
{
struct trace_iterator *iter = m->private;
static struct tracer *old_tracer;
int cpu_file = iter->cpu_file;
void *p = NULL;
loff_t l = 0;
int cpu;
/* copy the tracer to avoid using a global lock all around */
/*
* copy the tracer to avoid using a global lock all around.
* iter->trace is a copy of current_trace, the pointer to the
* name may be used instead of a strcmp(), as iter->trace->name
* will point to the same string as current_trace->name.
*/
mutex_lock(&trace_types_lock);
if (unlikely(old_tracer != current_trace && current_trace)) {
old_tracer = current_trace;
if (unlikely(current_trace && iter->trace->name != current_trace->name))
*iter->trace = *current_trace;
}
mutex_unlock(&trace_types_lock);
atomic_inc(&trace_record_cmdline_disabled);
@ -3494,7 +3496,6 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
size_t cnt, loff_t *ppos)
{
struct trace_iterator *iter = filp->private_data;
static struct tracer *old_tracer;
ssize_t sret;
/* return any leftover data */
@ -3506,10 +3507,8 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
/* copy the tracer to avoid using a global lock all around */
mutex_lock(&trace_types_lock);
if (unlikely(old_tracer != current_trace && current_trace)) {
old_tracer = current_trace;
if (unlikely(current_trace && iter->trace->name != current_trace->name))
*iter->trace = *current_trace;
}
mutex_unlock(&trace_types_lock);
/*
@ -3665,7 +3664,6 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
.ops = &tracing_pipe_buf_ops,
.spd_release = tracing_spd_release_pipe,
};
static struct tracer *old_tracer;
ssize_t ret;
size_t rem;
unsigned int i;
@ -3675,10 +3673,8 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
/* copy the tracer to avoid using a global lock all around */
mutex_lock(&trace_types_lock);
if (unlikely(old_tracer != current_trace && current_trace)) {
old_tracer = current_trace;
if (unlikely(current_trace && iter->trace->name != current_trace->name))
*iter->trace = *current_trace;
}
mutex_unlock(&trace_types_lock);
mutex_lock(&iter->mutex);