vhd-util : note on Xen/RAX images
Add a note covering what we've discovered about creating RAX/Xenserver compatible images over the last few days. Change-Id: Iffd9dab1ca54f27390ec7850093e828ca7576e98
This commit is contained in:
Ian Wienand
parent
b52b560fb0
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6758849b66
@ -11,6 +11,7 @@ Developer Guide
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developing_elements
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dib_lint
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stable_interfaces
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vhd_creation
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This documentation explains how to get started with creating your own
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disk-image-builder elements as well as some high level concepts for element
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248
doc/source/developer/vhd_creation.rst
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248
doc/source/developer/vhd_creation.rst
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@ -0,0 +1,248 @@
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vhd creation
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============
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There is currently a hard dependency on the patched version of
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``vhd-utils`` to create Xenserver VHD compatible images. The main
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target for these images is the Rackspace Public Cloud.
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This note should explain the current issues.
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The patch to include ``convert`` as an option to ``vhd-utils``,
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avaialble at https://github.com/citrix-openstack/xenserver-utils/, is
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built by infra into a PPA available at
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https://launchpad.net/~openstack-ci-core/+archive/ubuntu/vhd-util.
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Upstream Xen has actually removed all the code related to ``blktap2``
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with
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https://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=5c883cf036cf5ab8b1b79390549e2475f7a568dd.
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The tools have been removed from Debuntu with
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https://bugs.debian.org/917907. So this patch is even less trivial to
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apply; the project has seemingly been split into
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https://github.com/xapi-project/blktap/ but support status is unclear.
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It is tempting to use ``qemu-img`` image conversion routines. Indeed
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this supports converting RAW images to VPC output. However, VPC is a
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fairly flexible standard across a number of different hypervisors.
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The main standard is available from Microsoft at
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https://www.microsoft.com/en-us/download/confirmation.aspx?id=23850
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and is what ``qemu-img`` impelements.
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However, trying to boot an image created with this results in a
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"resize" error. This is described in
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https://bugs.launchpad.net/nova/+bug/862653 but comes down to the
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following in
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https://github.com/xapi-project/blktap/blob/master/vhd/lib/vhd-util-resize.c#L1055::
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if (!vhd_creator_tapdisk(&vhd)) {
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printf("%s not created by xen; resize not supported\n", name);
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err = -EINVAL;
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}
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It seems that Xen will refuse to grow a image without a creator
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``tap\0``. It is tempting to patch ``qemu-img`` to do this (patch
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follows for those interested). However, if you look at the output
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with ``vhd-util read -p -n ./<file>.vhd`` you will notice it complains
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about an invalid ``batmap``. The ``batmap`` appears to be a Xen
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extension to the VPC standard. Checking ``vhd_has_batmap`` at
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https://github.com/xen-project/xen/blob/365aabb6e5023cee476adf81106729efd49c644f/tools/blktap2/vhd/lib/libvhd.c#L1193
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it seems we can fool Xen by setting the vhd version tags low enough
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that it thinks the image doesn't have a ``batmap`` (i.e. presumably
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created with tools before ``batmap``'s existed).
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Side note: there is a bunch of qemu work to implement overlay VHD
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disks with
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https://patchwork.ozlabs.org/project/qemu-devel/list/?submitter=64750
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which has never merged. This also seems to include a ``batmap``
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implementation.
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With the full patch applied below, we get images that appear fairly
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similar from (patched) ``vhd-util`` and ``qemu-img``; generated from
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the same ``.raw`` file.
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qemu-img output::
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VHD Footer Summary:
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-------------------
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Cookie : conectix
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Features : (0x00000002) <RESV>
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File format version : Major: 1, Minor: 0
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Data offset : 512
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Timestamp : Wed Oct 30 06:25:41 2019
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Creator Application : 'tap'
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Creator version : Major: 1, Minor: 0
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Creator OS : Unknown!
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Original disk size : 16667 MB (17477591040 Bytes)
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Current disk size : 16667 MB (17477591040 Bytes)
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Geometry : Cyl: 33865, Hds: 16, Sctrs: 63
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: = 16667 MB (17477591040 Bytes)
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Disk type : Dynamic hard disk
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Checksum : 0xffffec8c|0xffffec8c (Good!)
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UUID : 1bfda481-dd4d-43aa-8f3a-84689b5ab3d7
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Saved state : No
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Hidden : 0
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VHD Header Summary:
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-------------------
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Cookie : cxsparse
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Data offset (unusd) : 18446744073709
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Table offset : 1536
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Header version : 0x00010000
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Max BAT size : 8334
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Block size : 2097152 (2 MB)
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Parent name :
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Parent UUID : 00000000-0000-0000-0000-000000000000
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Parent timestamp : Sat Jan 1 00:00:00 2000
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Checksum : 0xfffff3c9|0xfffff3c9 (Good!)
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vhd-utils output::
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VHD Footer Summary:
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-------------------
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Cookie : conectix
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Features : (0x00000002) <RESV>
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File format version : Major: 1, Minor: 0
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Data offset : 512
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Timestamp : Tue Oct 8 09:18:54 2019
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Creator Application : 'tap'
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Creator version : Major: 1, Minor: 3
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Creator OS : Unknown!
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Original disk size : 16668 MB (17477664768 Bytes)
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Current disk size : 16668 MB (17477664768 Bytes)
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Geometry : Cyl: 33865, Hds: 16, Sctrs: 63
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: = 16667 MB (17477591040 Bytes)
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Disk type : Dynamic hard disk
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Checksum : 0xffffeebb|0xffffeebb (Good!)
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UUID : 14f2710a-b9b8-48f7-94bb-005ba6d566b2
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Saved state : No
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Hidden : 0
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VHD Header Summary:
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-------------------
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Cookie : cxsparse
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Data offset (unusd) : 18446744073709
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Table offset : 1536
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Header version : 0x00010000
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Max BAT size : 8334
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Block size : 2097152 (2 MB)
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Parent name :
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Parent UUID : 00000000-0000-0000-0000-000000000000
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Parent timestamp : Sat Jan 1 00:00:00 2000
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Checksum : 0xfffff3c9|0xfffff3c9 (Good!)
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VHD Batmap Summary:
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-------------------
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Batmap offset : 35840
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Batmap size (secs) : 3
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Batmap version : 0x00010002
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Checksum : 0xfffbf214|0xfffbf214 (Good!)
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This does upload and boot in RAX, but the root disk does not appear to
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grow correctly.
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Emperically, it also seems that fixed sized disks (generated with
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``subformat=fixed``) will not import (at least into Rackspace). I
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also tried resizing the dynamic ``vhd`` (with ``vhd-util
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resize --debug -n ./test.vhd -s $((32 * 1024 * 1024 )) -j
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resize.log``), which looked correct in ``vhd-util`` output (``Current
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disk size`` grew) but Rackspace would not import this image.
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qemu patch
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==========
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Applies against qemu at HEAD
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``16884391c750d0c5e863f55ad7aaaa146fc5181e``
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::
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diff --git a/block/vpc.c b/block/vpc.c
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index a655502..d1716f0 100644
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--- a/block/vpc.c
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+++ b/block/vpc.c
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@@ -60,6 +60,7 @@ enum vhd_type {
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#define VHD_MAX_GEOMETRY (VHD_CHS_MAX_C * VHD_CHS_MAX_H * VHD_CHS_MAX_S)
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#define VPC_OPT_FORCE_SIZE "force_size"
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+#define VPC_OPT_XENSERVER_COMPAT "xenserver_compat"
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/* always big-endian */
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typedef struct vhd_footer {
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@@ -1042,12 +1043,16 @@ static int coroutine_fn vpc_co_create(BlockdevCreateOptions *opts,
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memset(buf, 0, 1024);
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memcpy(footer->creator, "conectix", 8);
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- if (vpc_opts->force_size) {
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+ if (vpc_opts->xenserver_compat) {
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+ memcpy(footer->creator_app, "tap\0", 4);
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+ memcpy(footer->creator_os, "\0\0\0\0", 4);
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+ } else if (vpc_opts->force_size) {
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memcpy(footer->creator_app, "qem2", 4);
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+ memcpy(footer->creator_os, "Wi2k", 4);
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} else {
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memcpy(footer->creator_app, "qemu", 4);
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+ memcpy(footer->creator_os, "Wi2k", 4);
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}
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- memcpy(footer->creator_os, "Wi2k", 4);
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footer->features = cpu_to_be32(0x02);
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footer->version = cpu_to_be32(0x00010000);
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@@ -1058,9 +1063,14 @@ static int coroutine_fn vpc_co_create(BlockdevCreateOptions *opts,
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}
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footer->timestamp = cpu_to_be32(time(NULL) - VHD_TIMESTAMP_BASE);
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- /* Version of Virtual PC 2007 */
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- footer->major = cpu_to_be16(0x0005);
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- footer->minor = cpu_to_be16(0x0003);
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+ if (vpc_opts->xenserver_compat) {
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+ footer->major = cpu_to_be16(0x0001);
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+ footer->minor = cpu_to_be16(0x0000);
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+ } else {
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+ /* Version of Virtual PC 2007 */
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+ footer->major = cpu_to_be16(0x0005);
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+ footer->minor = cpu_to_be16(0x0003);
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+ }
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footer->orig_size = cpu_to_be64(total_size);
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footer->current_size = cpu_to_be64(total_size);
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footer->cyls = cpu_to_be16(cyls);
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@@ -1101,6 +1111,7 @@ static int coroutine_fn vpc_co_create_opts(const char *filename,
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static const QDictRenames opt_renames[] = {
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{ VPC_OPT_FORCE_SIZE, "force-size" },
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+ { VPC_OPT_XENSERVER_COMPAT, "xenserver-compat" },
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{ NULL, NULL },
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};
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@@ -1220,6 +1231,11 @@ static QemuOptsList vpc_create_opts = {
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"specified, rather than using the nearest CHS-based "
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"calculation"
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},
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+ {
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+ .name = VPC_OPT_XENSERVER_COMPAT,
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+ .type = QEMU_OPT_BOOL,
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+ .help = "Set creator to tap"
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+ },
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{ /* end of list */ }
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}
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};
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diff --git a/qapi/block-core.json b/qapi/block-core.json
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index aa97ee2..68daa3c 100644
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--- a/qapi/block-core.json
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+++ b/qapi/block-core.json
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@@ -4669,6 +4669,7 @@
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# @force-size Force use of the exact byte size instead of rounding to the
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# next size that can be represented in CHS geometry
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# (default: false)
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+# @xenserver-compat Xenserver comapt
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#
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# Since: 2.12
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##
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@@ -4676,7 +4677,9 @@
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'data': { 'file': 'BlockdevRef',
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'size': 'size',
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'*subformat': 'BlockdevVpcSubformat',
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- '*force-size': 'bool' } }
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+ '*force-size': 'bool',
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+ '*xenserver-compat': 'bool'
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+ } }
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##
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# @BlockdevCreateOptions:
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