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[Qemu-devel] [PATCH V3 1/9] specs/qcow2: add compress format extension
From: |
Peter Lieven |
Subject: |
[Qemu-devel] [PATCH V3 1/9] specs/qcow2: add compress format extension |
Date: |
Fri, 14 Jul 2017 11:56:37 +0200 |
Signed-off-by: Peter Lieven <address@hidden>
---
docs/interop/qcow2.txt | 35 ++++++++++++++++++++++++++++++++++-
1 file changed, 34 insertions(+), 1 deletion(-)
diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt
index d7fdb1f..c2d3dab 100644
--- a/docs/interop/qcow2.txt
+++ b/docs/interop/qcow2.txt
@@ -86,7 +86,12 @@ in the description of a field.
be written to (unless for regaining
consistency).
- Bits 2-63: Reserved (set to 0)
+ Bit 2: Compress format bit. If and only if this bit
+ is set then the compress format extension
+ MUST be present and MUST be parsed and checked
+ for compatibility.
+
+ Bits 3-63: Reserved (set to 0)
80 - 87: compatible_features
Bitmask of compatible features. An implementation can
@@ -137,6 +142,7 @@ be stored. Each extension has a structure like the
following:
0x6803f857 - Feature name table
0x23852875 - Bitmaps extension
0x0537be77 - Full disk encryption header pointer
+ 0xC03183A3 - Compress format extension
other - Unknown header extension, can be safely
ignored
@@ -311,6 +317,33 @@ The algorithms used for encryption vary depending on the
method
in the LUKS header, with the physical disk sector as the
input tweak.
+
+== Compress format extension ==
+
+The compress format extension is an optional header extension. It provides
+the ability to specify the compress algorithm and compress parameters
+that are used for compressed clusters. This new header MUST be present if
+the incompatible-feature bit "compress format bit" is set and MUST be absent
+otherwise.
+
+The fields of the compress format extension are:
+
+ Byte 0 - 15: compress_format_name (padded with zeros, but not
+ necessarily null terminated if it has full length).
+ Valid compression format names currently are:
+
+ zlib: Standard zlib deflate compression
+
+ 16: compress_level (uint8_t)
+
+ 0 = default compress level (valid for all formats, default)
+
+ Additional valid compression levels for zlib compression:
+
+ All values between 1 and 9. 1 gives best speed, 9 gives best
+ compression.
+
+
== Host cluster management ==
qcow2 manages the allocation of host clusters by maintaining a reference count
--
1.9.1
- [Qemu-devel] [PATCH V3 0/9] add Qcow2 compress format extension, Peter Lieven, 2017/07/14
- [Qemu-devel] [PATCH V3 2/9] qapi/block-core: add Qcow2Compress parameters, Peter Lieven, 2017/07/14
- [Qemu-devel] [PATCH V3 1/9] specs/qcow2: add compress format extension,
Peter Lieven <=
- [Qemu-devel] [PATCH V3 3/9] block/qcow2: parse compress create options, Peter Lieven, 2017/07/14
- [Qemu-devel] [PATCH V3 8/9] block/qcow2: start using the compress format extension, Peter Lieven, 2017/07/14
- [Qemu-devel] [PATCH V3 5/9] block/qcow2: read and write the compress format extension, Peter Lieven, 2017/07/14
- [Qemu-devel] [PATCH V3 9/9] block/qcow2: add lzo compress format, Peter Lieven, 2017/07/14
- [Qemu-devel] [PATCH V3 7/9] block/qcow2: optimize qcow2_co_pwritev_compressed, Peter Lieven, 2017/07/14
- [Qemu-devel] [PATCH V3 4/9] qemu-img: add documentation for compress settings, Peter Lieven, 2017/07/14
- [Qemu-devel] [PATCH V3 6/9] block/qcow2: simplify ret usage in qcow2_create, Peter Lieven, 2017/07/14