From: Max Reitz <mreitz@redhat.com>
To: Alberto Garcia <berto@igalia.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, 1 Jul 2020 14:52:14 +0200 [thread overview]
Message-ID: <fae77394-92fd-d170-0ae6-051c0a024d04@redhat.com> (raw)
In-Reply-To: <6ee75696d3eaed56b46e91fe242fdfab51feb066.1593342067.git.berto@igalia.com>
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On 28.06.20 13:02, Alberto Garcia wrote:
> This patch adds QCow2SubclusterType, which is the subcluster-level
> version of QCow2ClusterType. All QCOW2_SUBCLUSTER_* values have the
> the same meaning as their QCOW2_CLUSTER_* equivalents (when they
> exist). See below for details and caveats.
>
> In images without extended L2 entries clusters are treated as having
> exactly one subcluster so it is possible to replace one data type with
> the other while keeping the exact same semantics.
>
> With extended L2 entries there are new possible values, and every
> subcluster in the same cluster can obviously have a different
> QCow2SubclusterType so functions need to be adapted to work on the
> subcluster level.
>
> There are several things that have to be taken into account:
>
> a) QCOW2_SUBCLUSTER_COMPRESSED means that the whole cluster is
> compressed. We do not support compression at the subcluster
> level.
>
> b) There are two different values for unallocated subclusters:
> QCOW2_SUBCLUSTER_UNALLOCATED_PLAIN which means that the whole
> cluster is unallocated, and QCOW2_SUBCLUSTER_UNALLOCATED_ALLOC
> which means that the cluster is allocated but the subcluster is
> not. The latter can only happen in images with extended L2
> entries.
>
> c) QCOW2_SUBCLUSTER_INVALID is used to detect the cases where an L2
> entry has a value that violates the specification. The caller is
> responsible for handling these situations.
>
> To prevent compatibility problems with images that have invalid
> values but are currently being read by QEMU without causing side
> effects, QCOW2_SUBCLUSTER_INVALID is only returned for images
> with extended L2 entries.
>
> qcow2_cluster_to_subcluster_type() is added as a separate function
> from qcow2_get_subcluster_type(), but this is only temporary and both
> will be merged in a subsequent patch.
>
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> ---
> block/qcow2.h | 126 +++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 125 insertions(+), 1 deletion(-)
>
> diff --git a/block/qcow2.h b/block/qcow2.h
> index 82b86f6cec..3aec6f452a 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
[...]
> @@ -634,9 +686,11 @@ static inline int64_t qcow2_vm_state_offset(BDRVQcow2State *s)
> static inline QCow2ClusterType qcow2_get_cluster_type(BlockDriverState *bs,
> uint64_t l2_entry)
> {
> + BDRVQcow2State *s = bs->opaque;
> +
> 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 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.
So...
> if (l2_entry & L2E_OFFSET_MASK) {
> return QCOW2_CLUSTER_ZERO_ALLOC;
> }
[...]
> +/*
> + * In an image without subsclusters @l2_bitmap is ignored and
> + * @sc_index must be 0.
> + * Return QCOW2_SUBCLUSTER_INVALID if an invalid l2 entry is detected
> + * (this checks the whole entry and bitmap, not only the bits related
> + * to subcluster @sc_index).
> + */
> +static inline
> +QCow2SubclusterType qcow2_get_subcluster_type(BlockDriverState *bs,
> + uint64_t l2_entry,
> + uint64_t l2_bitmap,
> + unsigned sc_index)
> +{
> + BDRVQcow2State *s = bs->opaque;
> + QCow2ClusterType type = qcow2_get_cluster_type(bs, l2_entry);
> + assert(sc_index < s->subclusters_per_cluster);
> +
> + if (has_subclusters(s)) {
> + switch (type) {
> + case QCOW2_CLUSTER_COMPRESSED:
> + return QCOW2_SUBCLUSTER_COMPRESSED;
> + case QCOW2_CLUSTER_NORMAL:
> + if ((l2_bitmap >> 32) & l2_bitmap) {
> + return QCOW2_SUBCLUSTER_INVALID;
> + } else if (l2_bitmap & QCOW_OFLAG_SUB_ZERO(sc_index)) {
> + return QCOW2_SUBCLUSTER_ZERO_ALLOC;
> + } else if (l2_bitmap & QCOW_OFLAG_SUB_ALLOC(sc_index)) {
> + return QCOW2_SUBCLUSTER_NORMAL;
> + } else {
> + return QCOW2_SUBCLUSTER_UNALLOCATED_ALLOC;
> + }
> + case QCOW2_CLUSTER_UNALLOCATED:
> + if (l2_bitmap & QCOW_L2_BITMAP_ALL_ALLOC) {
> + return QCOW2_SUBCLUSTER_INVALID;
> + } else if (l2_bitmap & QCOW_OFLAG_SUB_ZERO(sc_index)) {
> + return QCOW2_SUBCLUSTER_ZERO_PLAIN;
> + } else {
> + return QCOW2_SUBCLUSTER_UNALLOCATED_PLAIN;
> + }
...consequentially, this function no longer reports clusters which have
the zero flag set as invalid (which it did in v4, when I last looked at it).
I see this was a conscious choice of yours in v5. I don’t really see
the justification for it, though. As far as I can understand, you seem
to argue that no corruption detection is better than incomplete
corruption detection, and that a complete and thorough detection would
warrant its own series, do I understand that correctly?
Max
> + default:
> + g_assert_not_reached();
> + }
> + } else {
> + return qcow2_cluster_to_subcluster_type(type);
> + }
> +}
> +
> /* Check whether refcounts are eager or lazy */
> static inline bool qcow2_need_accurate_refcounts(BDRVQcow2State *s)
> {
>
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next prev parent reply other threads:[~2020-07-01 12:53 UTC|newest]
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 [this message]
2020-07-01 16:26 ` Alberto Garcia
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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