block/vpc: Fix size calculation

The size calculated from the CHS values is not the real image (disk) size,
but usually a smaller value. This is caused by rounding effects.

Only older operating systems use CHS. Such guests won't be able to use
the whole disk. All modern operating systems use the real size.

This patch fixes https://bugs.launchpad.net/qemu/+bug/1105670/.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Message-id: 1360265212-22037-1-git-send-email-sw@weilnetz.de
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

diff --git a/block/vpc.c b/block/vpc.c
index 82229ef5a00b5dc5e5d9f5e519820d85d2d507ae..b4ff5646a221058089c49b19235f4451f08a503d 100644 (file)
--- a/block/vpc.c
+++ b/block/vpc.c
@@ -34,6 +34,8 @@
 
 #define HEADER_SIZE 512
 
+#define VHD_SECTOR_SIZE 512
+
 //#define CACHE
 
 enum vhd_type {
@@ -204,11 +206,13 @@ static int vpc_open(BlockDriverState *bs, int flags)
     /* Write 'checksum' back to footer, or else will leave it with zero. */
     footer->checksum = be32_to_cpu(checksum);
 
-    // The visible size of a image in Virtual PC depends on the geometry
-    // rather than on the size stored in the footer (the size in the footer
-    // is too large usually)
-    bs->total_sectors = (int64_t)
-        be16_to_cpu(footer->cyls) * footer->heads * footer->secs_per_cyl;
+    /* The visible size of a image in Virtual PC depends on the guest:
+     * QEMU and other emulators report the real size (here in sectors).
+     * All modern operating systems use this real size.
+     * Very old operating systems use CHS values to calculate the total size.
+     * This calculated size is usually smaller than the real size.
+     */
+    bs->total_sectors = be64_to_cpu(footer->size) / VHD_SECTOR_SIZE;
 
     /* Allow a maximum disk size of approximately 2 TB */
     if (bs->total_sectors >= 65535LL * 255 * 255) {