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From: Max Reitz <mreitz@redhat.com>
To: qemu-block@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>,
	Peter Maydell <peter.maydell@linaro.org>,
	qemu-devel@nongnu.org, Max Reitz <mreitz@redhat.com>
Subject: [PULL 02/18] docs: qcow2: introduce compression type feature
Date: Thu, 20 Feb 2020 17:06:54 +0100	[thread overview]
Message-ID: <20200220160710.533297-3-mreitz@redhat.com> (raw)
In-Reply-To: <20200220160710.533297-1-mreitz@redhat.com>

From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.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>
---
 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



  parent reply	other threads:[~2020-02-20 16:09 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-20 16:06 [PULL 00/18] Block patches Max Reitz
2020-02-20 16:06 ` [PULL 01/18] docs: improve qcow2 spec about extending image header Max Reitz
2020-02-20 16:06 ` Max Reitz [this message]
2020-02-20 16:06 ` [PULL 03/18] iotests: Remove the superfluous 2nd check for the availability of quorum Max Reitz
2020-02-20 16:06 ` [PULL 04/18] iotests/147: Fix drive parameters Max Reitz
2020-02-20 16:06 ` [PULL 05/18] qapi: Allow getting flat output from 'query-named-block-nodes' Max Reitz
2020-02-20 16:06 ` [PULL 06/18] qemu-img: Add --target-is-zero to convert Max Reitz
2020-02-20 16:36   ` Eric Blake
2020-02-20 20:18     ` David Edmondson
2020-02-20 16:06 ` [PULL 07/18] block: always fill entire LUKS header space with zeros Max Reitz
2020-02-20 16:07 ` [PULL 08/18] block/backup-top: fix flags handling Max Reitz
2020-02-20 16:07 ` [PULL 09/18] iotests/279: Fix for non-qcow2 formats Max Reitz
2020-02-20 16:07 ` [PULL 10/18] block/nbd: Fix hang in .bdrv_close() Max Reitz
2020-02-20 16:07 ` [PULL 11/18] block: Generic file creation fallback Max Reitz
2020-02-25 10:05   ` Peter Maydell
2020-02-25 10:19     ` Max Reitz
2020-02-20 16:07 ` [PULL 12/18] file-posix: Drop hdev_co_create_opts() Max Reitz
2020-02-20 16:07 ` [PULL 13/18] iscsi: Drop iscsi_co_create_opts() Max Reitz
2020-02-20 16:07 ` [PULL 14/18] iotests: Add test for image creation fallback Max Reitz
2020-02-20 16:07 ` [PULL 15/18] qemu-img: Fix convert -n -B for backing-less targets Max Reitz
2020-02-20 16:07 ` [PULL 16/18] iotests: Test convert -n -B to backing-less target Max Reitz
2020-02-20 16:07 ` [PULL 17/18] block: Fix VM size field width in snapshot dump Max Reitz
2020-02-20 16:07 ` [PULL 18/18] iotests: Test snapshot -l field separation Max Reitz
2020-02-21 14:20 ` [PULL 00/18] Block patches Peter Maydell

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