Commit 694ce0a5 authored Jun 24, 2009 by Li Zefan Committed by Ingo Molnar Jun 24, 2009

ftrace: Don't manipulate @pos in t_start()



It's rather confusing that in t_start(), in some cases @pos is
incremented, and in some cases it's decremented and then incremented.

This patch rewrites t_start() in a much more general way.

Thus we fix a bug that if ftrace_filtered == 1, functions have tracer
hooks won't be printed, because the branch is always unreachable:

static void *t_start(...)
{
	...
	if (!p)
		return t_hash_start(m, pos);
	return p;
}

Before:
  # echo 'sys_open' > /mnt/tracing/set_ftrace_filter
  # echo 'sys_write:traceon:4' >> /mnt/tracing/set_ftrace_filter
  sys_open

After:
  # echo 'sys_open' > /mnt/tracing/set_ftrace_filter
  # echo 'sys_write:traceon:4' >> /mnt/tracing/set_ftrace_filter
  sys_open
  sys_write:traceon:count=4

Reviewed-by: Liming Wang <liming.wang@windriver.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <4A41874B.4090507@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 85951842

kernel/trace/ftrace.c

+8 −11

Original line number	Diff line number	Diff line
		@@ -1467,8 +1467,6 @@ t_next(struct seq_file m, void v, loff_t *pos)
		iter->pg = iter->pg->next;
		iter->idx = 0;
		goto retry;
		} else {
		iter->idx = -1;
		}
		} else {
		rec = &iter->pg->records[iter->idx++];
		@@ -1497,6 +1495,7 @@ static void t_start(struct seq_file m, loff_t *pos)
		{
		struct ftrace_iterator *iter = m->private;
		void *p = NULL;
		loff_t l;

		mutex_lock(&ftrace_lock);
		/*
		@@ -1508,23 +1507,21 @@ static void t_start(struct seq_file m, loff_t *pos)
		if (*pos > 0)
		return t_hash_start(m, pos);
		iter->flags \|= FTRACE_ITER_PRINTALL;
		(*pos)++;
		return iter;
		}

		if (iter->flags & FTRACE_ITER_HASH)
		return t_hash_start(m, pos);

		if (*pos > 0) {
		if (iter->idx < 0)
		return p;
		(*pos)--;
		iter->idx--;
		iter->pg = ftrace_pages_start;
		iter->idx = 0;
		for (l = 0; l <= *pos; ) {
		p = t_next(m, p, &l);
		if (!p)
		break;
		}

		p = t_next(m, p, pos);

		if (!p)
		if (!p && iter->flags & FTRACE_ITER_FILTER)
		return t_hash_start(m, pos);

		return p;

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