linux-kernel - Re: [PATCH 4/4] tracing: fix splice return too large

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Date:	Wed, 8 Apr 2009 11:55:09 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Steven Rostedt <srostedt@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] tracing: fix splice return too large


* Lai Jiangshan <laijs@...fujitsu.com> wrote:

> Ingo Molnar wrote:
> > * Lai Jiangshan <laijs@...fujitsu.com> wrote:
> > 
> >> -	for (i = 0; i < PIPE_BUFFERS && len; i++, len -= size) {
> >> +	if (*ppos & (PAGE_SIZE - 1)) {
> >> +		WARN_ONCE(1, "Ftrace: previous read must page-align\n");
> >> +		return -EINVAL;
> >> +	}
> >> +
> >> +	if (len & (PAGE_SIZE - 1)) {
> >> +		WARN_ONCE(1, "Ftrace: splice_read should page-align\n");
> >> +		if (len < PAGE_SIZE)
> >> +			return -EINVAL;
> >> +		len &= PAGE_MASK;
> >> +	}
> > 
> > Hm, the fix looks good, but is it a good idea to allow the 
> > triggering of this message from user-space?
> > 
> 
> But it is only triggered once.
> 
> If user get content from trace_pipe_raw with non-page-align, the 
> content is garbage. It's wasting, the kernel disallows it. This 
> message tell user why he read failed.
> 
> These 4 patches make trace_pipe_raw more robustious and consistent 
> (read by read(2) and splice). I focus on handling raw ftrace data 
> in userspace, these raw ftrace data should be trustiness.

Ok, agreed.

i've applied these four fixes from you to tip:tracing/splice, 
thanks. Steve: i think they are tracing/urgent material - do you 
agree?

	Ingo
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