Re: [RFC][PATCH -tip 1/5 V2] tracing: kprobe-tracer plugin core

[Masami Hiramatsu <mhiramat at redhat dot com>]

Frederic Weisbecker wrote:
> On Fri, Mar 20, 2009 at 09:33:30PM -0400, Masami Hiramatsu wrote:
>> Add kprobes based event tracer on ftrace.
>>
>> This tracer is similar to the events tracer which is based on Tracepoint
>> infrastructure. Instead of Tracepoint, this tracer is based on kprobes(kprobe
>> and kretprobe). It probes anywhere where kprobes can probe(this means, all
>> functions body except for __kprobes functions).
>>
>> changes from v1:
>>  - fix a bug in offset parsing.
>>  - use __trace_bprintk() instead of __trace_printk().
>>
>> Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
>> Cc: Steven Rostedt <rostedt@goodmis.org>
>> Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
>> Cc: Ingo Molnar <mingo@elte.hu>
>> Cc: Frederic Weisbecker <fweisbec@gmail.com>
>> ---
> 
> [ ... ]
> 
> 
>> +/* Probes listing interfaces */
>> +static void *probes_seq_start(struct seq_file *m, loff_t *pos)
>> +{
>> +	struct trace_probe *probe;
>> +	loff_t n = *pos;
>> +
>> +	mutex_lock(&probe_lock);
>> +	if (!list_empty(&probe_list)) {
>> +		list_for_each_entry(probe, &probe_list, list)
>> +			if (0 == n--)
>> +				return probe;
>> +	}
>> +	return NULL;
>> +}
>> +
>> +static void *probes_seq_next(struct seq_file *m, void *v, loff_t *pos)
>> +{
>> +	struct trace_probe *tp = v;
>> +
>> +	(*pos)++;
>> +	if (tp->list.next == &probe_list)
>> +		tp = NULL;
>> +	else
>> +		tp = list_entry(tp->list.next, struct trace_probe, list);
>> +	return tp;
>> +}
> 
> 
> 
> Hm, I think seq_list_start/next will be sufficient for your needs.

Oh, those look very useful, thanks!


>> +static void probes_seq_stop(struct seq_file *m, void *v)
>> +{
>> +	mutex_unlock(&probe_lock);
>> +}
>> +
>> +static int probes_seq_show(struct seq_file *m, void *v)
>> +{
>> +	struct trace_probe *tp = v;
>> +
>> +	if (tp == NULL)
>> +		return 0;
>> +
>> +	if (tp->symbol)
>> +		seq_printf(m, "%c %s%+ld\n",
>> +			probe_is_return(tp) ? 'r' : 'p',
>> +			probe_symbol(tp), probe_offset(tp));
>> +	else
>> +		seq_printf(m, "%c 0x%p\n",
>> +			probe_is_return(tp) ? 'r' : 'p',
>> +			probe_address(tp));
>> +	return 0;
>> +}
>> +
>> +static const struct seq_operations probes_seq_op = {
>> +	.start  = probes_seq_start,
>> +	.next   = probes_seq_next,
>> +	.stop   = probes_seq_stop,
>> +	.show   = probes_seq_show
>> +};
>> +
>> +static int probes_open(struct inode *inode, struct file *file)
>> +{
>> +	if ((file->f_mode & FMODE_WRITE) &&
>> +	    !(file->f_flags & O_APPEND))
>> +		cleanup_all_probes();
>> +
>> +	return seq_open(file, &probes_seq_op);
> 
> 
> This seq_open is only for read case. No?

Yes, but seq_release is called when closing. This seq_open is
for that. (you can see the similar coding in trace_events.c)

>> +}
>> +
>> +
>> +#define WRITE_BUFSIZE 128
>> +
>> +ssize_t probes_write(struct file *file, const char __user *buffer,
>> +		     size_t count, loff_t *ppos)
>> +{
>> +	char *kbuf, *tmp;
>> +	char **argv = NULL;
>> +	int argc = 0;
>> +	int ret;
>> +	size_t done;
>> +	size_t size;
>> +
>> +	if (!count || count < 0)
>> +		return 0;
>> +
>> +	kbuf = kmalloc(WRITE_BUFSIZE, GFP_KERNEL);
>> +	if (!kbuf)
>> +		return -ENOMEM;
>> +
>> +	ret = done = 0;
>> +	do {
>> +		size = count - done;
>> +		if (size > WRITE_BUFSIZE)
>> +			size = WRITE_BUFSIZE;
>> +		if (copy_from_user(kbuf, buffer + done, size)) {
>> +			ret = -EFAULT;
>> +			goto out;
>> +		}
>> +		kbuf[size] = '\0';
>> +		tmp = strchr(kbuf, '\n');
>> +		if (!tmp) {
>> +			pr_warning("Line length is too long: "
>> +				   "Should be less than %d.", WRITE_BUFSIZE);
>> +			ret = -EINVAL;
>> +			goto out;
>> +		}
>> +		*tmp = '\0';
>> +		size = tmp - kbuf + 1;
>> +		done += size;
>> +
>> +		argv = argv_split(GFP_KERNEL, kbuf, &argc);
>> +		if (!argv) {
>> +			ret = -ENOMEM;
>> +			goto out;
>> +		}
>> +
>> +		if (argc)
>> +			ret = create_trace_probe(argc, argv);
>> +
>> +		argv_free(argv);
>> +		if (ret < 0)
>> +			goto out;
>> +
>> +	} while (done < count);
>> +	ret = done;
>> +out:
>> +	kfree(kbuf);
>> +	return ret;
>> +}
>> +
>> +static const struct file_operations kprobe_points_ops = {
>> +	.owner          = THIS_MODULE,
>> +	.open           = probes_open,
>> +	.read           = seq_read,
>> +	.llseek         = seq_lseek,
>> +	.release        = seq_release,
>> +	.write		= probes_write,
>> +};
>> +
>> +/* event recording functions */
>> +static void kprobe_trace_record(unsigned long ip, struct trace_probe *tp,
>> +				struct pt_regs *regs)
>> +{
>> +	__trace_bprintk(ip, "%s%s%+ld\n",
>> +			probe_is_return(tp) ? "<-" : "@",
>> +			probe_symbol(tp), probe_offset(tp));
>> +}
>> +
>> +/* Make a debugfs interface for controling probe points */
>> +static __init int init_kprobe_trace(void)
>> +{
>> +	struct dentry *d_tracer;
>> +	struct dentry *entry;
>> +
>> +	d_tracer = tracing_init_dentry();
>> +	if (!d_tracer)
>> +		return 0;
>> +
>> +	entry = debugfs_create_file("kprobe_probes", 0444, d_tracer,
> 
> 
> Shouldn't it be 0644 ?
> Since its first intend, and the most important one, is to receive
> commands from user?

Yes, right...

Thank you for review!


-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com