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Re: [PATCH v9 14/34] qcow2: Add QCow2SubclusterType and qcow2_get_subclu
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From: |
Max Reitz |
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Subject: |
Re: [PATCH v9 14/34] qcow2: Add QCow2SubclusterType and qcow2_get_subcluster_type() |
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Date: |
Fri, 3 Jul 2020 09:17:24 +0200 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 |
On 03.07.20 00:00, Alberto Garcia wrote:
> On Thu 02 Jul 2020 11:57:46 AM CEST, Max Reitz wrote:
>>> The reason why we would want to check it is, of course, because that
>>> bit does have a meaning in regular L2 entries.
>>>
>>> But that bit is ignored in images with subclusters so the only reason
>>> why we would check it is to report corruption, not because we need to
>>> know its value.
>>
>> Sure. But isn’t that the whole point of having
>> QCOW2_SUBCLUSTER_INVALID in the first place?
>
> At the moment we're only returning QCOW2_SUBCLUSTER_INVALID in cases
> where there is no way to interpret the entry correctly: a) the
> allocation and zero bits are set for the same subcluster, and b) the
> allocation bit is set but the entry has no valid offset.
>
> It doesn't mean that we cannot use _SUBCLUSTER_INVALID for cases like
> the one we're discussing, but this one is different from the other two.
OK, that makes sense.
Max
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