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Subject[PATCH 2/3] tracing: Ignore mmiotrace from kernel commandline
From: "Ziqian SUN (Zamir)" <zsun@redhat.com>

The mmiotrace tracer cannot be enabled with ftrace=mmiotrace in kernel
commandline. With this patch, noboot is added to the tracer struct,
and when system boot with a tracer that has noboot=true, it will print
out a warning message and continue booting.

Link: http://lkml.kernel.org/r/1505111195-31942-1-git-send-email-zsun@redhat.com

Signed-off-by: Ziqian SUN (Zamir) <zsun@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/trace/trace.c | 7 +++++++
kernel/trace/trace.h | 2 ++
kernel/trace/trace_mmiotrace.c | 1 +
3 files changed, 10 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a7fb136da891..d3ca35f38803 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5364,6 +5364,13 @@ static int tracing_set_tracer(struct trace_array *tr, const char *buf)
if (t == tr->current_trace)
goto out;

+ /* Some tracers won't work on kernel command line */
+ if (system_state < SYSTEM_RUNNING && t->noboot) {
+ pr_warn("Tracer '%s' is not allowed on command line, ignored\n",
+ t->name);
+ goto out;
+ }
+
/* Some tracers are only allowed for the top level buffer */
if (!trace_ok_for_array(t, tr)) {
ret = -EINVAL;
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index fb5d54d0d1b3..652c682707cd 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -444,6 +444,8 @@ struct tracer {
#ifdef CONFIG_TRACER_MAX_TRACE
bool use_max_tr;
#endif
+ /* True if tracer cannot be enabled in kernel param */
+ bool noboot;
};


diff --git a/kernel/trace/trace_mmiotrace.c b/kernel/trace/trace_mmiotrace.c
index cd7480d0a201..dca78fc48439 100644
--- a/kernel/trace/trace_mmiotrace.c
+++ b/kernel/trace/trace_mmiotrace.c
@@ -282,6 +282,7 @@ static struct tracer mmio_tracer __read_mostly =
.close = mmio_close,
.read = mmio_read,
.print_line = mmio_print_line,
+ .noboot = true,
};

__init static int init_mmio_trace(void)
--
2.13.2

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