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SubjectRe: [PATCH] ftrace: ftrace_dump_on_oops=[tracer]
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On Sat, 2008-11-01 at 14:43 -0400, Steven Rostedt wrote:
> On Sat, 1 Nov 2008, Peter Zijlstra wrote:
>
> > seems useful to debug crashes that happen before I read userspace.
>
> Hmm, I think it might be better to separate this from the dump_on_oops.
> How about a ftrace_default_tracer parameter?
>
> If one is defined, it is activated as soon as it is initialized. This way
> we decouple the dump_on_oops, which we may not always want, and a way to
> start tracers before the switch to user space.

Like so?

---
Subject: ftrace: enable setting an ftrace tracer on boot
In order to facilitate early boot trouble, allow one to specify a tracer
on the kernel boot line.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index d2c115b..4d694fd 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -765,6 +765,14 @@ and is between 256 and 4096 characters. It is defined in the file
parameter will force ia64_sal_cache_flush to call
ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.

+ ftrace=[tracer]
+ [ftrace] will set and start the specified tracer
+ as early as possible in order to facilitate early
+ boot debugging.
+
+ ftrace_dump_on_oops
+ [ftrace] will dump the trace buffers on oops.
+
gamecon.map[2|3]=
[HW,JOY] Multisystem joystick and NES/SNES/PSX pad
support via parallel port (up to 5 devices per port)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5b8c90d..a85187a 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -79,6 +79,15 @@ static int tracing_disabled = 1;
*/
int ftrace_dump_on_oops;

+static int tracing_set_tracer(char *buf);
+
+static int __init set_ftrace(char *str)
+{
+ tracing_set_tracer(str);
+ return 1;
+}
+__setup("ftrace", set_ftrace);
+
static int __init set_ftrace_dump_on_oops(char *str)
{
ftrace_dump_on_oops = 1;
@@ -2394,29 +2403,11 @@ tracing_set_trace_read(struct file *filp, char __user *ubuf,
return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
}

-static ssize_t
-tracing_set_trace_write(struct file *filp, const char __user *ubuf,
- size_t cnt, loff_t *ppos)
+static int tracing_set_tracer(char *buf)
{
struct trace_array *tr = &global_trace;
struct tracer *t;
- char buf[max_tracer_type_len+1];
- int i;
- size_t ret;
-
- ret = cnt;
-
- if (cnt > max_tracer_type_len)
- cnt = max_tracer_type_len;
-
- if (copy_from_user(&buf, ubuf, cnt))
- return -EFAULT;
-
- buf[cnt] = 0;
-
- /* strip ending whitespace. */
- for (i = cnt - 1; i > 0 && isspace(buf[i]); i--)
- buf[i] = 0;
+ int ret = 0;

mutex_lock(&trace_types_lock);
for (t = trace_types; t; t = t->next) {
@@ -2440,6 +2431,33 @@ tracing_set_trace_write(struct file *filp, const char __user *ubuf,
out:
mutex_unlock(&trace_types_lock);

+ return ret;
+}
+
+static ssize_t
+tracing_set_trace_write(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ char buf[max_tracer_type_len+1];
+ int i;
+ size_t ret;
+
+ if (cnt > max_tracer_type_len)
+ cnt = max_tracer_type_len;
+
+ if (copy_from_user(&buf, ubuf, cnt))
+ return -EFAULT;
+
+ buf[cnt] = 0;
+
+ /* strip ending whitespace. */
+ for (i = cnt - 1; i > 0 && isspace(buf[i]); i--)
+ buf[i] = 0;
+
+ ret = tracing_set_tracer(buf);
+ if (!ret)
+ ret = cnt;
+
if (ret > 0)
filp->f_pos += ret;




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