qcow2_get_cluster_offset() takes an (unaligned) guest offset and
returns the (aligned) offset of the corresponding cluster in the qcow2
image.
In practice none of the callers need to know where the cluster starts
so this patch makes the function calculate and return the final host
offset
handle_alloc() creates a QCowL2Meta structure in order to update the
image metadata and perform the necessary copy-on-write operations.
This patch moves that code to a separate function so it can be used
from other places.
Signed-off-by: Alberto Garcia
Reviewed-by: Max Reitz
---
Like offset_into_cluster() and size_to_clusters(), but for
subclusters.
Signed-off-by: Alberto Garcia
Reviewed-by: Eric Blake
---
block/qcow2.h | 10 ++
1 file changed, 10 insertions(+)
diff --git a/block/qcow2.h b/block/qcow2.h
index 2503374677..4fe31adfd3 100644
--- a/block/qcow2.h
The offset field of an uncompressed cluster's L2 entry must be aligned
to the cluster size, otherwise it is invalid. If the cluster has no
data then it means that the offset points to a preallocation, so we
can clear the offset field without affecting the guest-visible data.
This is what 'qemu-img
When writing to a qcow2 file there are two functions that take a
virtual offset and return a host offset, possibly allocating new
clusters if necessary:
- handle_copied() looks for normal data clusters that are already
allocated and have a reference count of 1. In those clusters we
Traditional qcow2 images don't allow preallocation if a backing file
is set. This is because once a cluster is allocated there is no way to
tell that its data should be read from the backing file.
Extended L2 entries have individual allocation bits for each
subcluster, and therefore it is
The bdrv_co_pwrite_zeroes() call here fills complete clusters with
zeroes, but it can happen that some subclusters are not part of the
write request or the copy-on-write. This patch makes sure that only
the affected subclusters are overwritten.
A potential improvement would be to also fill with
Extended L2 entries are 128-bit wide: 64 bits for the entry itself and
64 bits for the subcluster allocation bitmap.
In order to support them correctly get/set_l2_entry() need to be
updated so they take the entry width into account in order to
calculate the correct offset.
This patch also adds
This function returns an integer that can be either an error code or a
cluster type (a value from the QCow2ClusterType enum).
We are going to start using subcluster types instead of cluster types
in some functions so it's better to use the exact data types instead
of integers for clarity and in
Now that the implementation of subclusters is complete we can finally
add the necessary options to create and read images with this feature,
which we call "extended L2 entries".
Signed-off-by: Alberto Garcia
Reviewed-by: Eric Blake
---
qapi/block-core.json | 7 +++
block/qcow2.h
Signed-off-by: Alberto Garcia
---
tests/qemu-iotests/271 | 901 +
tests/qemu-iotests/271.out | 724 +
tests/qemu-iotests/group | 1 +
3 files changed, 1626 insertions(+)
create mode 100755 tests/qemu-iotests/271
create
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
The L2 bitmap needs to be updated after each write to indicate what
new subclusters are now allocated. This needs to happen even if the
cluster was already allocated and the L2 entry was otherwise valid.
In some cases however a write operation doesn't need change the L2
bitmap (because all
qcow2 images with subclusters have 128-bit L2 entries. The first 64
bits contain the same information as traditional images and the last
64 bits form a bitmap with the status of each individual subcluster.
Because of that we cannot assume that L2 entries are sizeof(uint64_t)
anymore. This
The logic of this function remains pretty much the same, except that
it uses count_contiguous_subclusters(), which combines the logic of
count_contiguous_clusters() / count_contiguous_clusters_unallocated()
and checks individual subclusters.
qcow2_cluster_to_subcluster_type() is not necessary as
The size of an L2 entry is 64 bits, but if we want to have subclusters
we need extended L2 entries. This means that we have to access L2
tables and slices differently depending on whether an image has
extended L2 entries or not.
This patch replaces all l2_slice[] accesses with calls to
Hi,
here's the new version of the patches to add subcluster allocation
support to qcow2.
Please refer to the cover letter of the first version for a full
description of the patches:
https://lists.gnu.org/archive/html/qemu-block/2019-10/msg00983.html
The important change from v8 is patch 24.
We are going to need it in other places.
Signed-off-by: Alberto Garcia
Reviewed-by: Vladimir Sementsov-Ogievskiy
Reviewed-by: Max Reitz
---
block/qcow2-cluster.c | 34 +++---
1 file changed, 19 insertions(+), 15 deletions(-)
diff --git a/block/qcow2-cluster.c
Subcluster allocation in qcow2 is implemented by extending the
existing L2 table entries and adding additional information to
indicate the allocation status of each subcluster.
This patch documents the changes to the qcow2 format and how they
affect the calculation of the L2 cache size.
Compressed clusters always have the bitmap part of the extended L2
entry set to 0.
Signed-off-by: Alberto Garcia
Reviewed-by: Max Reitz
---
block/qcow2-cluster.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 2276cee6d6..deff838fe8
This function will be used by the qcow2 code to check if an image has
subclusters or not.
At the moment this simply returns false. Once all patches needed for
subcluster support are ready then QEMU will be able to create and
read images with subclusters and this function will return the actual
For a given offset, return the subcluster number within its cluster
(i.e. with 32 subclusters per cluster it returns a number between 0
and 31).
Signed-off-by: Alberto Garcia
Reviewed-by: Max Reitz
Reviewed-by: Vladimir Sementsov-Ogievskiy
---
block/qcow2.h | 5 +
1 file changed, 5
In order to support extended L2 entries some functions of the qcow2
driver need to start dealing with subclusters instead of clusters.
qcow2_get_host_offset() is modified to return the subcluster type
instead of the cluster type, and all callers are updated to replace
all values of
The file_cluster_offset field of Qcow2AioTask stores a cluster-aligned
host offset. In practice this is not very useful because all users(*)
of this structure need the final host offset into the cluster, which
they calculate using
host_offset = file_cluster_offset + offset_into_cluster(s,
If an image has subclusters then there are more copy-on-write
scenarios that we need to consider. Let's say we have a write request
from the middle of subcluster #3 until the end of the cluster:
1) If we are writing to a newly allocated cluster then we need
copy-on-write. The previous contents
This field allows us to indicate that the L2 metadata update does not
come from a write request with actual data but from a preallocation
request.
For traditional images this does not make any difference, but for
images with extended L2 entries this means that the clusters are
allocated normally
When dealing with subcluster types there is a new value called
QCOW2_SUBCLUSTER_UNALLOCATED_ALLOC that has no equivalent in
QCow2ClusterType.
This patch handles that value in all places where subcluster types
are processed.
Signed-off-by: Alberto Garcia
Reviewed-by: Max Reitz
Reviewed-by:
This helper function tells us if a cluster is allocated (that is,
there is an associated host offset for it).
Signed-off-by: Alberto Garcia
Reviewed-by: Eric Blake
---
block/qcow2.h | 6 ++
1 file changed, 6 insertions(+)
diff --git a/block/qcow2.h b/block/qcow2.h
index
This works now at the subcluster level and pwrite_zeroes_alignment is
updated accordingly.
qcow2_cluster_zeroize() is turned into qcow2_subcluster_zeroize() with
the following changes:
- The request can now be subcluster-aligned.
- The cluster-aligned body of the request is still zeroized
This patch adds the following new fields to BDRVQcow2State:
- subclusters_per_cluster: Number of subclusters in a cluster
- subcluster_size: The size of each subcluster, in bytes
- subcluster_bits: No. of bits so 1 << subcluster_bits = subcluster_size
Images without subclusters are treated as if
The QCOW_OFLAG_ZERO bit that indicates that a cluster reads as
zeroes is only used in standard L2 entries. Extended L2 entries use
individual 'all zeroes' bits for each subcluster.
This must be taken into account when updating the L2 entry and also
when deciding that an existing entry does not
There are situations in which we want to know how many contiguous
subclusters of the same type there are in a given cluster. This can be
done by simply iterating over the subclusters and repeatedly calling
qcow2_get_subcluster_type() for each one of them.
However once we determined the type of a
Extended L2 entries are bigger than normal L2 entries so this has an
impact on the amount of metadata needed for a qcow2 file.
Signed-off-by: Alberto Garcia
Reviewed-by: Max Reitz
---
block/qcow2.c | 20 +---
1 file changed, 13 insertions(+), 7 deletions(-)
diff --git
Two things need to be taken into account here:
1) With full_discard == true the L2 entry must be cleared completely.
This also includes the L2 bitmap if the image has extended L2
entries.
2) With full_discard == false we have to make the discarded cluster
read back as zeroes. With
This function is only used by qcow2_expand_zero_clusters() to
downgrade a qcow2 image to a previous version. This would require
transforming all extended L2 entries into normal L2 entries but this
is not a simple task and there are no plans to implement this at the
moment.
Signed-off-by: Alberto
On Thu, 2020-06-25 at 14:55 +0200, Max Reitz wrote:
> That the luks driver is present is little indication on whether it is
> actually working. Without the crypto libraries linked in, it does not
> work. So add this function, which tries to create a luks image to see
> whether that actually
On Thu, 2020-06-25 at 14:55 +0200, Max Reitz wrote:
> Right now, _filter_img_create just filters out everything that looks
> format-dependent, and applies some filename filters. That means that we
> have to add another filter line every time some format gets a new
> creation option. This can be
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