[Bug 1870098] Re: [block/vpc] dynamic disk header: off-by-one error for "num_bat_entries"

[Kevin Wolf]

As I don't have your email address, I could not CC you on the patch
email. Can you please verify if the following patch on the mailing list
fixes your problem?

https://lists.gnu.org/archive/html/qemu-block/2020-04/msg00086.html

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https://bugs.launchpad.net/bugs/1870098

Title:
  [block/vpc] dynamic disk header: off-by-one error for
  "num_bat_entries"

Status in QEMU:
  New

Bug description:
  In current qemu versions (observed in 5.0.0-rc1 as well as
  2833ad487cfff7dc33703e4731b75facde1c561e), disk headers for dynamic
  VPCs are written with an incorrect "block allocation table entries"
  value.

  https://www.microsoft.com/en-us/download/details.aspx?id=23850 (the
  corresponding spec) states that:

  "Max Table Entries
  This field holds the maximum entries present in the BAT. This should be equal 
to the number of blocks in the disk (that is, the disk size divided by the 
block size)."

  Inside the qemu code, the value is "disk size divided by the block
  size *plus one*".

  Calculating "num_bat_entries" as "total_sectors/(block_size / 512)"
  *should* fix the issue.

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