linux-kernel - Re: [RFC PATCH 2/2] trace: splice support for tracing

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Message-ID: <20090211123526.GF16535@elte.hu>
Date:	Wed, 11 Feb 2009 13:35:26 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>,
	fweisbec@...il.com, penberg@...helsinki.fi,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 2/2] trace: splice support for tracing_pipe


* Steven Rostedt <rostedt@...dmis.org> wrote:

> On Mon, 9 Feb 2009, Eduard - Gabriel Munteanu wrote:
> > +
> > +static ssize_t tracing_splice_read_pipe(struct file *filp,
> > +					loff_t *ppos,
> > +					struct pipe_inode_info *pipe,
> > +					size_t len,
> > +					unsigned int flags)
> > +{
> > +	struct page *pages[PIPE_BUFFERS];
> > +	struct partial_page partial[PIPE_BUFFERS];
> > +	struct trace_iterator *iter = filp->private_data;
> > +	struct splice_pipe_desc spd = {
> > +		.pages = pages,
> > +		.partial = partial,
> > +		.nr_pages = 0, /* This gets updated below. */
> > +		.flags = flags,
> > +		.ops = &tracing_pipe_buf_ops,
> > +		.spd_release = tracing_spd_release_pipe,
> > +	};
> 
> Note, this is getting a little stack heavy. It is still in bounds,
> but I get very nervous when I see structure arrays on the stack.
> If either the structure or the array grows large, we can be in trouble.

Good point - but note that this is how splice support is implemented in
a number of other files - so if PIPE_BUFFERS or partial_page grows in
size, those places will fail too.

	Ingo
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