linux-kernel - Re: [PATCH 2/3] devmem: handle partial kmem write/read

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Date:	Tue, 15 Sep 2009 11:38:11 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Greg KH <greg@...ah.com>, Andi Kleen <andi@...stfloor.org>,
	Christoph Lameter <clameter@....com>,
	Ingo Molnar <mingo@...e.hu>, Tejun Heo <tj@...nel.org>,
	Nick Piggin <npiggin@...e.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] devmem: handle partial kmem write/read

On Tue, 15 Sep 2009 10:18:53 +0800
Wu Fengguang <fengguang.wu@...el.com> wrote:

> Return early on partial read/write, which may happen in future.
> (eg. hit hwpoison pages)
> 
Hmm, please modify vread() as you did in vwrite() and

==
               kbuf = (char *)__get_free_page(GFP_KERNEL);
                if (!kbuf)
                        return -ENOMEM;
==
Add __GFP_ZERO to kbuf allocation, and just ignore vread()'s return value.
Then, this will be much simpler.
Thanks,
-Kame


> CC: Greg KH <greg@...ah.com>
> CC: Andi Kleen <andi@...stfloor.org>
> CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> ---
>  drivers/char/mem.c |   30 ++++++++++++++++++------------
>  mm/vmalloc.c       |   10 +---------
>  2 files changed, 19 insertions(+), 21 deletions(-)
> 
> --- linux-mm.orig/drivers/char/mem.c	2009-09-15 09:44:49.000000000 +0800
> +++ linux-mm/drivers/char/mem.c	2009-09-15 09:44:55.000000000 +0800
> @@ -444,18 +444,22 @@ static ssize_t read_kmem(struct file *fi
>  		if (!kbuf)
>  			return -ENOMEM;
>  		while (count > 0) {
> +			unsigned long n;
> +
>  			sz = size_inside_page(p, count);
> -			sz = vread(kbuf, (char *)p, sz);
> -			if (!sz)
> +			n = vread(kbuf, (char *)p, sz);
> +			if (!n)
>  				break;
> -			if (copy_to_user(buf, kbuf, sz)) {
> +			if (copy_to_user(buf, kbuf, n)) {
>  				free_page((unsigned long)kbuf);
>  				return -EFAULT;
>  			}
> -			count -= sz;
> -			buf += sz;
> -			read += sz;
> -			p += sz;
> +			count -= n;
> +			buf += n;
> +			read += n;
> +			p += n;
> +			if (n < sz)
> +				break;
>  		}
>  		free_page((unsigned long)kbuf);
>  	}
> @@ -551,11 +555,13 @@ static ssize_t write_kmem(struct file * 
>  				free_page((unsigned long)kbuf);
>  				return -EFAULT;
>  			}
> -			sz = vwrite(kbuf, (char *)p, sz);
> -			count -= sz;
> -			buf += sz;
> -			virtr += sz;
> -			p += sz;
> +			n = vwrite(kbuf, (char *)p, sz);
> +			count -= n;
> +			buf += n;
> +			virtr += n;
> +			p += n;
> +			if (n < sz)
> +				break;
>  		}
>  		free_page((unsigned long)kbuf);
>  	}
> 
> -- 
> 
> --
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