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[PULL 02/18] docs: qcow2: introduce compression type feature
From: |
Max Reitz |
Subject: |
[PULL 02/18] docs: qcow2: introduce compression type feature |
Date: |
Thu, 20 Feb 2020 17:06:54 +0100 |
From: Vladimir Sementsov-Ogievskiy <address@hidden>
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 <address@hidden>
Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
Message-Id: <address@hidden>
[mreitz: s/Bits 3-63: Reserved/Bits 4-63: Reserved/]
Signed-off-by: Max Reitz <address@hidden>
---
docs/interop/qcow2.txt | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)
diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt
index 823cc266e0..5597e24474 100644
--- a/docs/interop/qcow2.txt
+++ b/docs/interop/qcow2.txt
@@ -109,7 +109,12 @@ the next fields through header_length.
An External Data File Name header extension may
be present if this bit is set.
- Bits 3-63: Reserved (set to 0)
+ Bit 3: Compression type bit. If this bit is set,
+ a non-default compression is used for
compressed
+ clusters. The compression_type field must be
+ present and not zero.
+
+ Bits 4-63: Reserved (set to 0)
80 - 87: compatible_features
Bitmask of compatible features. An implementation can
@@ -190,7 +195,19 @@ present*, if not altered by a specific incompatible bit.
to the field's offset. Also, all additional fields are not present for
version 2.
- < ... No additional fields in the header currently ... >
+ 104: compression_type
+
+ Defines the compression method used for compressed
clusters.
+ All compressed clusters in an image use the same
compression
+ type.
+
+ If the incompatible bit "Compression type" is set: the
field
+ must be present and non-zero (which means non-zlib
+ compression type). Otherwise, this field must not be
present
+ or must be zero (which means zlib).
+
+ Available compression type values:
+ 0: zlib <https://www.zlib.net/>
=== Header padding ===
--
2.24.1
- [PULL 00/18] Block patches, Max Reitz, 2020/02/20
- [PULL 01/18] docs: improve qcow2 spec about extending image header, Max Reitz, 2020/02/20
- [PULL 02/18] docs: qcow2: introduce compression type feature,
Max Reitz <=
- [PULL 03/18] iotests: Remove the superfluous 2nd check for the availability of quorum, Max Reitz, 2020/02/20
- [PULL 04/18] iotests/147: Fix drive parameters, Max Reitz, 2020/02/20
- [PULL 05/18] qapi: Allow getting flat output from 'query-named-block-nodes', Max Reitz, 2020/02/20
- [PULL 06/18] qemu-img: Add --target-is-zero to convert, Max Reitz, 2020/02/20
- [PULL 07/18] block: always fill entire LUKS header space with zeros, Max Reitz, 2020/02/20
- [PULL 08/18] block/backup-top: fix flags handling, Max Reitz, 2020/02/20
- [PULL 09/18] iotests/279: Fix for non-qcow2 formats, Max Reitz, 2020/02/20
- [PULL 10/18] block/nbd: Fix hang in .bdrv_close(), Max Reitz, 2020/02/20