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[Qemu-devel] [PATCH 3/5] vpc: Ignore geometry for large images

From: Peter Lieven
Subject: [Qemu-devel] [PATCH 3/5] vpc: Ignore geometry for large images
Date: Mon, 23 Feb 2015 15:27:39 +0100

From: Kevin Wolf <address@hidden>

The CHS calculation as done per the VHD spec imposes a maximum image
size of ~127 GB. Real VHD images exist that are larger than that.

Apparently there are two separate non-standard ways to achieve this:
You could use more heads than the spec does - this is the option that
qemu-img create chooses.

However, other images exist where the geometry is set to the maximum
(65536/16/255), but the actual image size is larger. Until now, such
images are truncated at 127 GB when opening them with qemu.

This patch changes the vpc driver to ignore geometry in this case and
only trust the size field in the header.

Signed-off-by: Kevin Wolf <address@hidden>
 block/vpc.c |   10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/block/vpc.c b/block/vpc.c
index 4e5ba85..11d3c86 100644
--- a/block/vpc.c
+++ b/block/vpc.c
@@ -215,12 +215,10 @@ static int vpc_open(BlockDriverState *bs, QDict *options, 
int flags,
     bs->total_sectors = (int64_t)
         be16_to_cpu(footer->cyls) * footer->heads * footer->secs_per_cyl;
-    /* images created with disk2vhd report a far higher virtual size
-     * than expected with the cyls * heads * sectors_per_cyl formula.
-     * use the footer->size instead if the image was created with
-     * disk2vhd.
-     */
-    if (!strncmp(footer->creator_app, "d2v", 4)) {
+    /* Images that have exactly the maximum geometry are probably bigger and
+     * would be truncated if we adhered to the geometry for them. Rely on
+     * footer->size for them. */
+    if (bs->total_sectors == 65535ULL * 16 * 255) {
         bs->total_sectors = be64_to_cpu(footer->size) / BDRV_SECTOR_SIZE;

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