linux-kernel - Re: [RFC][PATCH] introduce SIZE

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Date:	Fri, 20 Apr 2012 16:03:37 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Xi Wang <xi.wang@...il.com>
Cc:	linux-kernel@...r.kernel.org, Alex Elder <elder@...amhost.com>,
	David Airlie <airlied@...ux.ie>,
	Pekka Enberg <penberg@...nel.org>
Subject: Re: [RFC][PATCH] introduce SIZE_MAX

On Thu, 19 Apr 2012 00:27:51 -0400
Xi Wang <xi.wang@...il.com> wrote:

> ULONG_MAX is often used to check for integer overflow when calculating
> allocation size.  While ULONG_MAX happens to work on most systems,
> there is no guarantee that `size_t' must be the same size as `long'.
> 
> This patch introduces SIZE_MAX, the maximum value of `size_t', to
> improve portability and readability for allocation size validation.
>
> ...
>
> @@ -331,7 +331,7 @@ static int build_snap_context(struct ceph_snap_realm *realm)
>  
>  	/* alloc new snap context */
>  	err = -ENOMEM;
> -	if (num > (ULONG_MAX - sizeof(*snapc)) / sizeof(u64))
> +	if (num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))
>  		goto fail;
>  	snapc = kzalloc(sizeof(*snapc) + num*sizeof(u64), GFP_NOFS);
>  	if (!snapc)

hm, yes, I suppose that's better - hardwiring the assumption that
size_t has type unsigned long is pretty ugly.

Will we need something for ssize_t also?
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