linux-kernel - Re: [PATCH 3/3] tracing: clean up splice code

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Date:	Mon, 9 Feb 2009 20:25:01 +0200
From:	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 3/3] tracing: clean up splice code

On Mon, Feb 09, 2009 at 12:28:33PM -0500, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@...hat.com>
> 
> Ingo Molnar suggested a series of clean ups for the splice code.
> This patch implements those suggestions.
> 
> Signed-off-by: Steven Rostedt <srostedt@...hat.com>
> ---
>  kernel/trace/trace.c |   96 ++++++++++++++++++++++++++++---------------------
>  1 files changed, 55 insertions(+), 41 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 11fde0a..d898212 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2537,15 +2537,49 @@ static void tracing_spd_release_pipe(struct splice_pipe_desc *spd,
>  }
>  
>  static struct pipe_buf_operations tracing_pipe_buf_ops = {
> -	.can_merge = 0,
> -	.map = generic_pipe_buf_map,
> -	.unmap = generic_pipe_buf_unmap,
> -	.confirm = generic_pipe_buf_confirm,
> -	.release = tracing_pipe_buf_release,
> -	.steal = generic_pipe_buf_steal,
> -	.get = generic_pipe_buf_get,
> +	.can_merge		= 0,
> +	.map			= generic_pipe_buf_map,
> +	.unmap			= generic_pipe_buf_unmap,
> +	.confirm		= generic_pipe_buf_confirm,
> +	.release		= tracing_pipe_buf_release,
> +	.steal			= generic_pipe_buf_steal,
> +	.get			= generic_pipe_buf_get,
>  };
>  
> +static size_t
> +tracing_fill_pipe_page(struct page *pages, size_t rem,
> +			struct trace_iterator *iter)
> +{
> +	size_t count;
> +	int ret;
> +
> +	/* Seq buffer is page-sized, exactly what we need. */
> +	for (;;) {
> +		count = iter->seq.len;
> +		ret = print_trace_line(iter);
> +		count = iter->seq.len - count;
> +		if (rem < count) {
> +			rem = 0;
> +			iter->seq.len -= count;
> +			break;
> +		}
> +		if (ret == TRACE_TYPE_PARTIAL_LINE) {
> +			iter->seq.len -= count;
> +			break;
> +		}
> +
> +		trace_consume(iter);
> +		rem -= count;
> +		if (!find_next_entry_inc(iter))	{
> +			rem = 0;
> +			iter->ent = NULL;
> +			break;
> +		}
> +	}
> +
> +	return rem;
> +}
> +
>  static ssize_t tracing_splice_read_pipe(struct file *filp,
>  					loff_t *ppos,
>  					struct pipe_inode_info *pipe,
> @@ -2556,15 +2590,15 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
>  	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,
> +		.pages		= pages,
> +		.partial	= partial,
> +		.nr_pages	= 0, /* This gets updated below. */
> +		.flags		= flags,
> +		.ops		= &tracing_pipe_buf_ops,
> +		.spd_release	= tracing_spd_release_pipe,
>  	};
>  	ssize_t ret;
> -	size_t count, rem;
> +	size_t rem;
>  	unsigned int i;
>  
>  	mutex_lock(&trace_types_lock);
> @@ -2573,45 +2607,25 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
>  		ret = iter->trace->splice_read(iter, filp,
>  					       ppos, pipe, len, flags);
>  		if (ret)
> -			goto out;
> +			goto out_err;
>  	}
>  
>  	ret = tracing_wait_pipe(filp);
>  	if (ret <= 0)
> -		goto out;
> +		goto out_err;
>  
>  	if (!iter->ent && !find_next_entry_inc(iter)) {
>  		ret = -EFAULT;
> -		goto out;
> +		goto out_err;
>  	}
>  
>  	/* Fill as many pages as possible. */
>  	for (i = 0, rem = len; i < PIPE_BUFFERS && rem; i++) {
>  		pages[i] = alloc_page(GFP_KERNEL);
> +		if (!pages[i])
> +			break;

I believe you should decrement 'i' before breaking, since we fill
spd.nr_pages just after the loop. In case the current page couldn't be
allocated, spd.nr_pages will be one too many (that is, 'i').

>  
> -		/* Seq buffer is page-sized, exactly what we need. */
> -		for (;;) {
> -			count = iter->seq.len;
> -			ret = print_trace_line(iter);
> -			count = iter->seq.len - count;
> -			if (rem < count) {
> -				rem = 0;
> -				iter->seq.len -= count;
> -				break;
> -			}
> -			if (ret == TRACE_TYPE_PARTIAL_LINE) {
> -				iter->seq.len -= count;
> -				break;
> -			}
> -
> -			trace_consume(iter);
> -			rem -= count;
> -			if (!find_next_entry_inc(iter))	{
> -				rem = 0;
> -				iter->ent = NULL;
> -				break;
> -			}
> -		}
> +		rem = tracing_fill_pipe_page(pages[i], rem, iter);
>  
>  		/* Copy the data into the page, so we can start over. */
>  		ret = trace_seq_to_buffer(&iter->seq,
> @@ -2633,7 +2647,7 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
>  
>  	return splice_to_pipe(pipe, &spd);
>  
> -out:
> +out_err:
>  	mutex_unlock(&trace_types_lock);
>  
>  	return ret;
> -- 
> 1.5.6.5
> 
> -- 

Otherwise, it looks okay to me.


	Thanks,
	Eduard

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