[PATCH v2] tracing: Apply tracer specific options from kernel command line.

Jiaxing Wang
2015-11-04T01:14:44Z

Currently, the trace_options parameter is only applied in
tracer_alloc_buffers() when global_trace.current_trace is nop_trace,
so a tracer specific option will not be applied even when the specific
tracer is also enabled from kernel command line. For example, the
'func_stack_trace' option can't be enabled with the following kernel
parameter:

ftrace=function ftrace_filter=kfree trace_options=func_stack_trace

We can enable tracer specific options by simply apply the options again
if the specific tracer is also supplied from command line and started
in register_tracer().

To make trace_boot_options_buf can be parsed again, a comma and a space
is put back if they were replaced by strsep and strstrip respectively.

Also make register_tracer() be __init to access the __init data, and
in fact register_tracer is only called from __init code.

Signed-off-by: Jiaxing Wang <hello.wjx@gmail.com>
---
kernel/trace/trace.c | 45 ++++++++++++++++++++++++++++++++++++---------
1 file changed, 36 insertions(+), 9 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 6dd064e..689886c 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -214,12 +214,10 @@ __setup("alloc_snapshot", boot_alloc_snapshot);

static char trace_boot_options_buf[MAX_TRACER_SIZE] __initdata;
-static char *trace_boot_options __initdata;

static int __init set_trace_boot_options(char *str)
{
strlcpy(trace_boot_options_buf, str, MAX_TRACER_SIZE);
- trace_boot_options = trace_boot_options_buf;
return 0;
}
__setup("trace_options=", set_trace_boot_options);
@@ -1204,13 +1202,15 @@ static inline int run_tracer_selftest(struct tracer *type)
}
#endif /* CONFIG_FTRACE_STARTUP_TEST */

+static void __init apply_trace_boot_options(void);
+
/**
* register_tracer - register a tracer with the ftrace system.
* @type - the plugin for the tracer
*
* Register a new plugin tracer.
*/
-int register_tracer(struct tracer *type)
+int __init register_tracer(struct tracer *type)
{
struct tracer *t;
int ret = 0;
@@ -1268,6 +1268,9 @@ int register_tracer(struct tracer *type)
/* Do we want this tracer to start on bootup? */
tracing_set_tracer(&global_trace, type->name);
default_bootup_tracer = NULL;
+
+ apply_trace_boot_options();
+
/* disable other selftests, since this will break it. */
tracing_selftest_disabled = true;
#ifdef CONFIG_FTRACE_STARTUP_TEST
@@ -3577,6 +3580,7 @@ static int trace_set_options(struct trace_array *tr, char *option)
int neg = 0;
int ret = -ENODEV;
int i;
+ size_t orig_len = strlen(option);

cmp = strstrip(option);

@@ -3600,9 +3604,37 @@ static int trace_set_options(struct trace_array *tr, char *option)

mutex_unlock(&trace_types_lock);

+ /*
+ * If the first trailing whitespace is replaced with '\0' by strstrip,
+ * turn it back into a space.
+ */
+ if (orig_len > strlen(option))
+ option[strlen(option)] = ' ';
+
return ret;
}

+static void __init apply_trace_boot_options(void)
+{
+ char *buf = trace_boot_options_buf;
+ char *option;
+
+ while (true) {
+ option = strsep(&buf, ",");
+
+ if (!option)
+ break;
+ if (!*option)
+ continue;
+
+ trace_set_options(&global_trace, option);
+
+ /* Put back the comma to allow this to be called again */
+ if (buf)
+ *(buf - 1) = ',';
+ }
+}
+
static ssize_t
tracing_trace_options_write(struct file *filp, const char __user *ubuf,
size_t cnt, loff_t *ppos)
@@ -7153,12 +7185,7 @@ __init static int tracer_alloc_buffers(void)
INIT_LIST_HEAD(&global_trace.events);
list_add(&global_trace.list, &ftrace_trace_arrays);

- while (trace_boot_options) {
- char *option;
-
- option = strsep(&trace_boot_options, ",");
- trace_set_options(&global_trace, option);
- }
+ apply_trace_boot_options();

register_snapshot_cmd();

--
2.1.4