linux-kernel - Re: [PATCH 1/3] vmalloc: ignore vmalloc area holes in vwrite()

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Date:	Tue, 15 Sep 2009 11:34:25 +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>,
	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 1/3] vmalloc: ignore vmalloc area holes in vwrite()

On Tue, 15 Sep 2009 10:18:52 +0800
Wu Fengguang <fengguang.wu@...el.com> wrote:

> Siliently ignore all vmalloc area holes in vwrite(),
> and report success to the caller even if nothing is written.
> 
> CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>

Why don't you modify vread() at the same time ?
Because /proc/kcore ignores return value of vread(), I think you can
modify it without no side-effect.

Regards,
-Kame

> ---
>  mm/vmalloc.c |   13 ++-----------
>  1 file changed, 2 insertions(+), 11 deletions(-)
> 
> --- linux-mm.orig/mm/vmalloc.c	2009-09-15 10:08:33.000000000 +0800
> +++ linux-mm/mm/vmalloc.c	2009-09-15 10:14:18.000000000 +0800
> @@ -1805,10 +1805,8 @@ finished:
>   *	@addr:		vm address.
>   *	@count:		number of bytes to be read.
>   *
> - *	Returns # of bytes which addr and buf should be incresed.
> + *	Returns # of bytes which addr and buf should be increased.
>   *	(same number to @count).
> - *	If [addr...addr+count) doesn't includes any intersect with valid
> - *	vmalloc area, returns 0.
>   *
>   *	This function checks that addr is a valid vmalloc'ed area, and
>   *	copy data from a buffer to the given addr. If specified range of
> @@ -1816,8 +1814,6 @@ finished:
>   *	proper area of @buf. If there are memory holes, no copy to hole.
>   *	IOREMAP area is treated as memory hole and no copy is done.
>   *
> - *	If [addr...addr+count) doesn't includes any intersects with alive
> - *	vm_struct area, returns 0.
>   *	@buf should be kernel's buffer. Because	this function uses KM_USER0,
>   *	the caller should guarantee KM_USER0 is not used.
>   *
> @@ -1834,7 +1830,6 @@ long vwrite(char *buf, char *addr, unsig
>  	struct vm_struct *tmp;
>  	char *vaddr;
>  	unsigned long n, buflen;
> -	int copied = 0;
>  
>  	/* Don't allow overflow */
>  	if ((unsigned long) addr + count < count)
> @@ -1856,18 +1851,14 @@ long vwrite(char *buf, char *addr, unsig
>  		n = vaddr + tmp->size - PAGE_SIZE - addr;
>  		if (n > count)
>  			n = count;
> -		if (!(tmp->flags & VM_IOREMAP)) {
> +		if (!(tmp->flags & VM_IOREMAP))
>  			aligned_vwrite(buf, addr, n);
> -			copied++;
> -		}
>  		buf += n;
>  		addr += n;
>  		count -= n;
>  	}
>  finished:
>  	read_unlock(&vmlist_lock);
> -	if (!copied)
> -		return 0;
>  	return buflen;
>  }
>  
> 
> -- 
> 
> 

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