From mboxrd@z Thu Jan  1 00:00:00 1970
From: Kevin Wolf <kwolf@redhat.com>
Subject: Re: [RFC PATCH] kvm tools, qcow: Add support for growing refcount
 blocks
Date: Mon, 12 Dec 2011 12:17:49 +0100
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Cc: Lan Tianyu <tianyu.lan@intel.com>, kvm@vger.kernel.org,
	asias.hejun@gmail.com, levinsasha928@gmail.com,
	prasadjoshi124@gmail.com
To: Pekka Enberg <penberg@kernel.org>
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Am 12.12.2011 12:15, schrieb Kevin Wolf:
> Am 12.12.2011 11:58, schrieb Pekka Enberg:
>> On Mon, 12 Dec 2011, Kevin Wolf wrote:
>>>> @@ -667,14 +722,11 @@ static struct qcow_refcount_block *qcow_read_refcount_block(struct qcow *q, u64
>>>>
>>>>  	rft_idx = clust_idx >> (header->cluster_bits - QCOW_REFCOUNT_BLOCK_SHIFT);
>>>>  	if (rft_idx >= rft->rf_size)
>>>> -		return NULL;
>>>> +		return (void *)-ENOSPC;
>>>
>>> Is this allowed style in kvm-tool? :-/
>>
>> It needs to use ERR_PTR() and related macros but otherwise I don't see a 
>> big problem with it.
> 
> Can you be sure that it never clashes with a valid allocation when you
> use this in userspace?

Er, not sure what I was thinking, but it's the top 4k of the address
space, which should be kernel memory. So I think you actually can be sure.

Kevin