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From 6fb76589c86264784014d8b555dc9c479c534898 Mon Sep 17 00:00:00 2001
From: Jeffrey Cody <>
Date: Tue, 27 May 2014 19:05:11 +0200
Subject: [PATCH 07/13] block: vhdx - account for identical header sections
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RH-Author: Jeffrey Cody <>
Message-id: <>
Patchwork-id: 59040
O-Subject: [PATCH qemu-kvm RHEL7.1] block: vhdx - account for identical header sections
Bugzilla: 1097020
RH-Acked-by: Laszlo Ersek <>
RH-Acked-by: Fam Zheng <>
RH-Acked-by: Kevin Wolf <>

The VHDX spec v1.00 declares that "a header is current if it is the only
valid header or if it is valid and its SequenceNumber field is greater
than the other header’s SequenceNumber field. The parser must only use
data from the current header. If there is no current header, then the
VHDX file is corrupt."

However, the Disk2VHD tool from Microsoft creates a VHDX image file that
has 2 identical headers, including matching checksums and matching
sequence numbers.  Likely, as a shortcut the tool is just writing the
header twice, for the active and inactive headers, during the image
creation.  Technically, this should be considered a corrupt VHDX file
(at least per the 1.00 spec, and that is how we currently treat it).

But in order to accomodate images created with Disk2VHD, we can safely
create an exception for this case.  If we find identical sequence
numbers, then we check the VHDXHeader-sized chunks of each 64KB header
sections (we won't rely just on the crc32c to indicate the headers are
the same).  If they are identical, then we go ahead and use the first

Reported-by: Nerijus Baliūnas <>
Signed-off-by: Jeff Cody <>
Signed-off-by: Kevin Wolf <>
(cherry picked from commit 6906046169ffa9d829beeeaafe1fadeba51669fb)


Signed-off-by: Jeff Cody <>
BZ: 1097020

Conflict notes: the conflict was with the ret value; current upstream
                removed that in favor of passing in errp to the function

 block/vhdx.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

Signed-off-by: Miroslav Rezanina <>
 block/vhdx.c |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/block/vhdx.c b/block/vhdx.c
index 66a25c9..21ad6ad 100644
--- a/block/vhdx.c
+++ b/block/vhdx.c
@@ -473,8 +473,15 @@ static int vhdx_parse_header(BlockDriverState *bs, BDRVVHDXState *s)
         } else if (h2_seq > h1_seq) {
             s->curr_header = 1;
         } else {
-            ret = -EINVAL;
-            goto fail;
+            /* The Microsoft Disk2VHD tool will create 2 identical
+             * headers, with identical sequence numbers.  If the headers are
+             * identical, don't consider the file corrupt */
+            if (!memcmp(header1, header2, sizeof(VHDXHeader))) {
+                s->curr_header = 0;
+            } else {
+                ret = -EINVAL;
+                goto fail;
+            }