linux-kernel - Re: [PATCH 6/9] platform: goldfish: pipe: Fail compilation if structs are too large

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Message-ID: <a7a81091a1856bcd2ec7dd6a17270dd999058475.camel@perches.com>
Date:   Mon, 13 Aug 2018 18:48:02 -0700
From:   Joe Perches <joe@...ches.com>
To:     rkir@...gle.com, gregkh@...uxfoundation.org
Cc:     linux-kernel@...r.kernel.org, tkjos@...gle.com
Subject: Re: [PATCH 6/9] platform: goldfish: pipe: Fail compilation if
 structs are too large

On Mon, 2018-08-13 at 16:38 -0700, rkir@...gle.com wrote:
> From: Roman Kiryanov <rkir@...gle.com>
> 
> Since the driver provides no workaround prevent in cases if structs do
> no fit into a memory page, it is better to fail complation to find about
> the issue earlt instead of returning errors at runtime.

Minor earlt/early typo

> diff --git a/drivers/platform/goldfish/goldfish_pipe.c b/drivers/platform/goldfish/goldfish_pipe.c
[]
> @@ -797,9 +798,7 @@ static int goldfish_pipe_device_init(struct platform_device *pdev)
>  	 * needs to be contained in a single physical page. The easiest choice
>  	 * is to just allocate a page and place the buffers in it.
>  	 */
> -	if (WARN_ON(sizeof(*dev->buffers) > PAGE_SIZE))
> -		return -ENOMEM;
> -
> +	BUILD_BUG_ON(sizeof(*dev->buffers) > PAGE_SIZE);
>  	page = (char *)__get_free_page(GFP_KERNEL);
>  	if (!page) {
>  		kfree(dev->pipes);
> @@ -842,8 +841,7 @@ static int goldfish_pipe_probe(struct platform_device *pdev)
>  	struct resource *r;
>  	struct goldfish_pipe_dev *dev = pipe_dev;
>  
> -	if (WARN_ON(sizeof(struct goldfish_pipe_command) > PAGE_SIZE))
> -		return -ENOMEM;
> +	BUILD_BUG_ON(sizeof(struct goldfish_pipe_command) > PAGE_SIZE);
>  
>  	/* not thread safe, but this should not happen */
>  	WARN_ON(dev->base != NULL);

Why separate these BUILD_BUG_ONs into 2 different functions?

Why not just
	BUILD_BUG_ON(sizeof(struct goldfish_pipe_command) > PAGE_SIZE);
	BUILD_BUG_ON(sizeof(struct goldfish_pipe_dev_buffers) > PAGE_SIZE);