zstd significantly reduces cluster compression time.
It provides better compression performance maintaining
the same level of the compression ratio in comparison with
zlib, which, at the moment, is the only compression
method available.
The performance test results:
Test compresses and decompresses qemu qcow2 image with just
installed rhel-7.6 guest.
Image cluster size: 64K. Image on disk size: 2.2G
The test was conducted with brd disk to reduce the influence
of disk subsystem to the test results.
The results is given in seconds.
compress cmd:
time ./qemu-img convert -O qcow2 -c -o compression_type=[zlib|zstd]
src.img [zlib|zstd]_compressed.img
decompress cmd
time ./qemu-img convert -O qcow2
[zlib|zstd]_compressed.img uncompressed.img
compression decompression
zlib zstd zlib zstd
------------------------------------------------------------
real 65.5 16.3 (-75 %) 1.9 1.6 (-16 %)
user 65.0 15.8 5.3 2.5
sys 3.3 0.2 2.0 2.0
Both ZLIB and ZSTD gave the same compression ratio: 1.57
compressed image size in both cases: 1.4G
Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
QAPI part:
Acked-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200507082521.29210-4-dplotnikov@virtuozzo.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Backing files and raw external data files are mutually exclusive.
The documentation of the raw external data bit (in autoclear_features)
already indicates that, but we should also mention it on the other
side.
Suggested-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-Id: <20200410121816.8334-1-berto@igalia.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
The feature table is supposed to advertise the name of all feature
bits that we support; however, we forgot to update the table for
autoclear bits. While at it, move the table to read-only memory in
code, and tweak the qcow2 spec to name the second autoclear bit.
Update iotests that are affected by the longer header length.
Fixes: 88ddffae
Fixes: 93c24936
Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20200324174233.1622067-3-eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
The patch adds a new additional field to the qcow2 header: compression_type,
which specifies compression type. If field is absent or zero, default
compression type is set: ZLIB, which corresponds to current behavior.
New compression type (ZSTD) is to be added in further commit.
Suggested-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20200131142219.3264-3-vsementsov@virtuozzo.com>
[mreitz: s/Bits 3-63: Reserved/Bits 4-63: Reserved/]
Signed-off-by: Max Reitz <mreitz@redhat.com>
Make it more obvious how to add new fields to the version 3 header and
how to interpret them.
The specification is adjusted so that for new defined optional fields:
1. Software may support some of these optional fields and ignore the
others, which means that features may be backported to downstream
Qemu independently.
2. If we want to add incompatible field (or a field, for which some of
its values would be incompatible), it must be accompanied by
incompatible feature bit.
Also the concept of "default is zero" is clarified, as it's strange to
say that the value of the field is assumed to be zero for the software
version which don't know about the field at all and don't know how to
treat it be it zero or not.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200131142219.3264-2-vsementsov@virtuozzo.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
[mreitz: s/some its/some of its/]
Signed-off-by: Max Reitz <mreitz@redhat.com>
We already use (we didn't notice it) IN_USE flag for marking bitmap
metadata outdated, such as AUTO flag, which mirrors enabled/disabled
bitmaps. Now we are going to support bitmap resize, so it's good to
write IN_USE meaning with more details.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-id: 20190311185147.52309-2-vsementsov@virtuozzo.com
Signed-off-by: John Snow <jsnow@redhat.com>
Be more specific about the string representation in header extensions.
Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Although off_t permits up to 63 bits (8EB) of file offsets, in
practice, we're going to hit other limits first. Document some
of those limits in the qcow2 spec (some are inherent, others are
implementation choices of qemu), and how choice of cluster size
can influence some of the limits.
While we cannot map any uncompressed virtual cluster to any
address higher than 64 PB (56 bits) (due to the current L1/L2
field encoding stopping at bit 55), qemu's cap of 8M for the
refcount table can still access larger host addresses for some
combinations of large clusters and small refcount_order. For
comparison, ext4 with 4k blocks caps files at 16PB.
Another interesting limit: for compressed clusters, the L2 layout
requires an ever-smaller maximum host offset as cluster size gets
larger, down to a 512 TB maximum with 2M clusters. In particular,
note that with a cluster size of 8k or smaller, the L2 entry for
a compressed cluster could technically point beyond the 64PB mark,
but when you consider that with 8k clusters and refcount_order = 0,
you cannot access beyond 512T without exceeding qemu's limit of an
8M cap on the refcount table, it is unlikely that any image in the
wild has attempted to do so. To be safe, let's document that bits
beyond 55 in a compressed cluster must be 0.
Signed-off-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Ville Skyttä <ville.skytta@iki.fi>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 20180612065150.21110-1-ville.skytta@iki.fi
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Compressed clusters are not supposed to have the COPIED bit set, but
this is not made explicit in the specs, so let's document it.
Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-id: 74552e1d6e858d3159cb0c0e188e80bc9248e337.1523376013.git.berto@igalia.com
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
This patch fixes several mistakes in the documentation of the
compressed cluster descriptor:
1) the documentation claims that the cluster descriptor contains the
number of sectors used to store the compressed data, but what it
actually contains is the number of sectors *minus one* or, in other
words, the number of additional sectors after the first one.
2) the width of the fields is incorrectly specified. The number of bits
used by each field is
x = 62 - (cluster_bits - 8) for the offset field
y = (cluster_bits - 8) for the size field
So the offset field's location is [0, x-1], not [0, x] as stated.
3) the size field does not contain the size of the compressed data,
but rather the number of sectors where that data is stored. The
compressed data starts at the exact point specified in the offset
field and ends when there's enough data to produce a cluster of
decompressed data. Both points can be in the middle of a sector,
allowing several compressed clusters to be stored next to one
another, sharing sectors if necessary.
Cc: qemu-stable@nongnu.org
Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
A bitmap directory entry is sometimes called a 'bitmap header'. This
patch leaves only one name - 'bitmap directory entry'. The name 'bitmap
header' creates misunderstandings with 'qcow2 header' and 'qcow2 bitmap
header extension' (which is extension of qcow2 header)
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-id: 20170628120530.31251-3-vsementsov@virtuozzo.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-id: 20170628120530.31251-2-vsementsov@virtuozzo.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
Update the qcow2 specification to describe how the LUKS header is
placed inside a qcow2 file, when using LUKS encryption for the
qcow2 payload instead of the legacy AES-CBC encryption
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 20170623162419.26068-13-berrange@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
This is for the future interoperability & management guide. It includes
the QAPI docs, including the automatically generated ones, other socket
protocols (vhost-user, VNC), and the qcow2 file format.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
