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From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: qemu-devel@nongnu.org, Kevin Wolf <kwolf@redhat.com>,
Hanna Reitz <hreitz@redhat.com>, qemu-block@nongnu.org
Cc: Eric Blake <eblake@redhat.com>
Subject: [PATCH v3] vpc: Read images exported from Azure correctly
Date: Thu, 12 Dec 2024 13:25:12 +0100
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It was found that 'qemu-nbd' is not able to work with some disk images
exported from Azure. Looking at the 512b footer (which contains VPC
metadata):
00000000 63 6f 6e 65 63 74 69 78 00 00 00 02 00 01 00 00 |conectix......=
..|
00000010 ff ff ff ff ff ff ff ff 2e c7 9b 96 77 61 00 00 |............wa=
..|
00000020 00 07 00 00 57 69 32 6b 00 00 00 01 40 00 00 00 |....Wi2k....@.=
..|
00000030 00 00 00 01 40 00 00 00 28 a2 10 3f 00 00 00 02 |....@...(..?..=
..|
00000040 ff ff e7 47 8c 54 df 94 bd 35 71 4c 94 5f e5 44 |...G.T...5qL._=
.D|
00000050 44 53 92 1a 00 00 00 00 00 00 00 00 00 00 00 00 |DS............=
..|
00000060 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |..............=
..|
we can see that Azure uses a different 'Creator application' --
'wa\0\0' (offset 0x1c, likely reads as 'Windows Azure') and QEMU uses this
field to determine how it can get image size. Apparently, Azure uses 'new'
method, just like Hyper-V.
Overall, it seems that only VPC and old QEMUs need to be ignored as all new
creator apps seem to have reliable current_size. Invert the logic and make
'current_size' method the default to avoid adding every new creator app to
the list.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
Changes since v1/v2: invert the logic and make 'vpc' and 'qemu' use CHS
while defaulting to current_size.
---
block/vpc.c | 65 ++++++++++++++++++++++++++++-------------------------
1 file changed, 35 insertions(+), 30 deletions(-)
diff --git a/block/vpc.c b/block/vpc.c
index d95a204612b7..e22d4bfe3fc1 100644
--- a/block/vpc.c
+++ b/block/vpc.c
@@ -216,6 +216,39 @@ static void vpc_parse_options(BlockDriverState *bs, Qe=
muOpts *opts,
}
}
=20
+/*
+ * Microsoft Virtual PC and Microsoft Hyper-V produce and read
+ * VHD image sizes differently. VPC will rely on CHS geometry,
+ * while Hyper-V and disk2vhd use the size specified in the footer.
+ *
+ * We use a couple of approaches to try and determine the correct method:
+ * look at the Creator App field, and look for images that have CHS
+ * geometry that is the maximum value.
+ *
+ * If the CHS geometry is the maximum CHS geometry, then we assume that
+ * the size is the footer->current_size to avoid truncation. Otherwise,
+ * we follow the table based on footer->creator_app:
+ *
+ * Currently known creator apps:
+ * 'vpc ' : CHS Virtual PC (uses disk geometry)
+ * 'qemu' : CHS QEMU (uses disk geometry)
+ * 'qem2' : current_size QEMU (uses current_size)
+ * 'win ' : current_size Hyper-V
+ * 'd2v ' : current_size Disk2vhd
+ * 'tap\0' : current_size XenServer
+ * 'CTXS' : current_size XenConverter
+ * 'wa\0\0': current_size Azure
+ *
+ * The user can override the table values via drive options, however
+ * even with an override we will still use current_size for images
+ * that have CHS geometry of the maximum size.
+ */
+static bool vpc_ignore_current_size(VHDFooter *footer)
+{
+ return !strncmp(footer->creator_app, "vpc ", 4) ||
+ !strncmp(footer->creator_app, "qemu", 4);
+}
+
static int vpc_open(BlockDriverState *bs, QDict *options, int flags,
Error **errp)
{
@@ -304,36 +337,8 @@ static int vpc_open(BlockDriverState *bs, QDict *optio=
ns, int flags,
bs->total_sectors =3D (int64_t)
be16_to_cpu(footer->cyls) * footer->heads * footer->secs_per_cyl;
=20
- /* Microsoft Virtual PC and Microsoft Hyper-V produce and read
- * VHD image sizes differently. VPC will rely on CHS geometry,
- * while Hyper-V and disk2vhd use the size specified in the footer.
- *
- * We use a couple of approaches to try and determine the correct meth=
od:
- * look at the Creator App field, and look for images that have CHS
- * geometry that is the maximum value.
- *
- * If the CHS geometry is the maximum CHS geometry, then we assume that
- * the size is the footer->current_size to avoid truncation. Otherwis=
e,
- * we follow the table based on footer->creator_app:
- *
- * Known creator apps:
- * 'vpc ' : CHS Virtual PC (uses disk geometry)
- * 'qemu' : CHS QEMU (uses disk geometry)
- * 'qem2' : current_size QEMU (uses current_size)
- * 'win ' : current_size Hyper-V
- * 'd2v ' : current_size Disk2vhd
- * 'tap\0' : current_size XenServer
- * 'CTXS' : current_size XenConverter
- *
- * The user can override the table values via drive options, however
- * even with an override we will still use current_size for images
- * that have CHS geometry of the maximum size.
- */
- use_chs =3D (!!strncmp(footer->creator_app, "win ", 4) &&
- !!strncmp(footer->creator_app, "qem2", 4) &&
- !!strncmp(footer->creator_app, "d2v ", 4) &&
- !!strncmp(footer->creator_app, "CTXS", 4) &&
- !!memcmp(footer->creator_app, "tap", 4)) || s->force_use_ch=
s;
+ /* Use CHS or current_size to determine the image size */
+ use_chs =3D vpc_ignore_current_size(footer) || s->force_use_chs;
=20
if (!use_chs || bs->total_sectors =3D=3D VHD_MAX_GEOMETRY || s->force_=
use_sz) {
bs->total_sectors =3D be64_to_cpu(footer->current_size) /
--=20
2.47.0