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[PATCH v10 2/2] docs: qcow2: introduce compression type feature
From: |
Vladimir Sementsov-Ogievskiy |
Subject: |
[PATCH v10 2/2] docs: qcow2: introduce compression type feature |
Date: |
Mon, 20 Jan 2020 20:13:45 +0300 |
The patch add new additional field to 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>
---
docs/interop/qcow2.txt | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt
index 355925c35e..4569f0dba3 100644
--- a/docs/interop/qcow2.txt
+++ b/docs/interop/qcow2.txt
@@ -109,6 +109,11 @@ the next fields through header_length.
An External Data File Name header extension may
be present if this bit is set.
+ 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 3-63: Reserved (set to 0)
80 - 87: compatible_features
@@ -189,7 +194,16 @@ present*, if not altered by a specific incompatible bit.
*. A field is considered not present when header_length is less or equal 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 ===
--
2.21.0