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From: Alberto Garcia <berto@igalia.com>
To: Max Reitz <mreitz@redhat.com>, qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, Derek Su <dereksu@qnap.com>,
	Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
	qemu-block@nongnu.org
Subject: Re: [PATCH v9 14/34] qcow2: Add QCow2SubclusterType and qcow2_get_subcluster_type()
Date: Wed, 01 Jul 2020 18:26:01 +0200
Message-ID: <w51mu4jurqe.fsf@maestria.local.igalia.com> (raw)
In-Reply-To: <fae77394-92fd-d170-0ae6-051c0a024d04@redhat.com>

On Wed 01 Jul 2020 02:52:14 PM CEST, Max Reitz wrote:
>>      if (l2_entry & QCOW_OFLAG_COMPRESSED) {
>>          return QCOW2_CLUSTER_COMPRESSED;
>> -    } else if (l2_entry & QCOW_OFLAG_ZERO) {
>> +    } else if ((l2_entry & QCOW_OFLAG_ZERO) && !has_subclusters(s)) {
>
> OK, so now qcow2_get_cluster_type() reports zero clusters to be normal
> or unallocated clusters when there are subclusters.  Seems weird to
> me, because zero clusters are invalid clusters then.

I'm actually hesitant about this.

In extended L2 entries QCOW_OFLAG_ZERO does not have any meaning so
technically it doesn't need to be checked any more than the other
reserved bits (1 to 8).

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.

It's true that we do check it in v2 images, although in that case the
entries are otherwise identical and there is a way to convert between
both types.

> I preferred just reporting them as zero clusters and letting the
> caller deal with it, because it does mean an error in the image and so
> it should be reported.

Another alternative would be to add QCOW2_CLUSTER_INVALID and we could
even include there other cases like unaligned offsets and things like
that. But that would also affect the code that repairs corrupted images.

Berto


  reply index

Thread overview: 71+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-28 11:02 [PATCH v9 00/34] Add subcluster allocation to qcow2 Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 01/34] qcow2: Make Qcow2AioTask store the full host offset Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 02/34] qcow2: Convert qcow2_get_cluster_offset() into qcow2_get_host_offset() Alberto Garcia
2020-06-30 10:19   ` Max Reitz
2020-06-30 10:27     ` Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 03/34] qcow2: Add calculate_l2_meta() Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 04/34] qcow2: Split cluster_needs_cow() out of count_cow_clusters() Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 05/34] qcow2: Process QCOW2_CLUSTER_ZERO_ALLOC clusters in handle_copied() Alberto Garcia
2020-06-30 10:38   ` Max Reitz
2020-06-28 11:02 ` [PATCH v9 06/34] qcow2: Add get_l2_entry() and set_l2_entry() Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 07/34] qcow2: Document the Extended L2 Entries feature Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 08/34] qcow2: Add dummy has_subclusters() function Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 09/34] qcow2: Add subcluster-related fields to BDRVQcow2State Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 10/34] qcow2: Add offset_to_sc_index() Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 11/34] qcow2: Add offset_into_subcluster() and size_to_subclusters() Alberto Garcia
2020-07-01 12:23   ` Max Reitz
2020-06-28 11:02 ` [PATCH v9 12/34] qcow2: Add l2_entry_size() Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 13/34] qcow2: Update get/set_l2_entry() and add get/set_l2_bitmap() Alberto Garcia
2020-07-01 12:28   ` Max Reitz
2020-06-28 11:02 ` [PATCH v9 14/34] qcow2: Add QCow2SubclusterType and qcow2_get_subcluster_type() Alberto Garcia
2020-07-01 12:52   ` Max Reitz
2020-07-01 16:26     ` Alberto Garcia [this message]
2020-07-02  9:57       ` Max Reitz
2020-07-02 22:00         ` Alberto Garcia
2020-07-03  7:17           ` Max Reitz
2020-06-28 11:02 ` [PATCH v9 15/34] qcow2: Add qcow2_get_subcluster_range_type() Alberto Garcia
2020-07-01 13:37   ` Max Reitz
2020-06-28 11:02 ` [PATCH v9 16/34] qcow2: Add qcow2_cluster_is_allocated() Alberto Garcia
2020-07-01 13:55   ` Max Reitz
2020-06-28 11:02 ` [PATCH v9 17/34] qcow2: Add cluster type parameter to qcow2_get_host_offset() Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 18/34] qcow2: Replace QCOW2_CLUSTER_* with QCOW2_SUBCLUSTER_* Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 19/34] qcow2: Handle QCOW2_SUBCLUSTER_UNALLOCATED_ALLOC Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 20/34] qcow2: Add subcluster support to calculate_l2_meta() Alberto Garcia
2020-07-02 11:30   ` Max Reitz
2020-06-28 11:02 ` [PATCH v9 21/34] qcow2: Add subcluster support to qcow2_get_host_offset() Alberto Garcia
2020-07-02 12:46   ` Max Reitz
2020-07-02 22:04     ` Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 22/34] qcow2: Add subcluster support to zero_in_l2_slice() Alberto Garcia
2020-07-02 12:56   ` Max Reitz
2020-06-28 11:02 ` [PATCH v9 23/34] qcow2: Add subcluster support to discard_in_l2_slice() Alberto Garcia
2020-07-02 13:24   ` Max Reitz
2020-06-28 11:02 ` [PATCH v9 24/34] qcow2: Add subcluster support to check_refcounts_l2() Alberto Garcia
2020-07-02 13:32   ` Max Reitz
2020-06-28 11:02 ` [PATCH v9 25/34] qcow2: Update L2 bitmap in qcow2_alloc_cluster_link_l2() Alberto Garcia
2020-07-02 14:01   ` Max Reitz
2020-06-28 11:02 ` [PATCH v9 26/34] qcow2: Clear the L2 bitmap when allocating a compressed cluster Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 27/34] qcow2: Add subcluster support to handle_alloc_space() Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 28/34] qcow2: Add subcluster support to qcow2_co_pwrite_zeroes() Alberto Garcia
2020-07-02 14:28   ` Max Reitz
2020-07-02 22:40     ` Alberto Garcia
2020-07-03  7:18       ` Max Reitz
2020-06-28 11:02 ` [PATCH v9 29/34] qcow2: Add subcluster support to qcow2_measure() Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 30/34] qcow2: Add prealloc field to QCowL2Meta Alberto Garcia
2020-07-02 14:50   ` Max Reitz
2020-07-02 14:58     ` Eric Blake
2020-07-02 15:09       ` Max Reitz
2020-07-02 23:05         ` Alberto Garcia
2020-07-03  7:22           ` Max Reitz
2020-06-28 11:02 ` [PATCH v9 31/34] qcow2: Add the 'extended_l2' option and the QCOW2_INCOMPAT_EXTL2 bit Alberto Garcia
2020-07-02 15:13   ` Max Reitz
2020-07-03 12:43     ` Alberto Garcia
2020-06-28 11:02 ` [PATCH v9 32/34] qcow2: Allow preallocation and backing files if extended_l2 is set Alberto Garcia
2020-07-03  7:45   ` Max Reitz
2020-06-28 11:02 ` [PATCH v9 33/34] qcow2: Assert that expand_zero_clusters_in_l1() does not support subclusters Alberto Garcia
2020-07-03  7:46   ` Max Reitz
2020-06-28 11:02 ` [PATCH v9 34/34] iotests: Add tests for qcow2 images with extended L2 entries Alberto Garcia
2020-07-03  9:49   ` Max Reitz
2020-07-03 13:06     ` Alberto Garcia
2020-07-03 13:47       ` Max Reitz
2020-07-03 15:20         ` Alberto Garcia
2020-07-06 13:57       ` Eric Blake

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