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 12:15:25 +0100
Message-ID: <4EE5E24D.20300@redhat.com>
References: <1323655410-32000-1-git-send-email-tianyu.lan@intel.com> <4EE5CFA0.5000203@redhat.com> <alpine.LFD.2.02.1112121257150.7537@tux.localdomain>
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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 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?

But yes, at least using appropriate functions should be required. And
this means that you can't only check for -ENOSPC, but you need to check
for all possible error codes (IS_ERR_VALUE() I guess).

Kevin