Commit cdf9634b authored Jan 20, 2015 by Jeff Cody Committed by Max Reitz Jan 23, 2015

block: vhdx - force FileOffsetMB field to '0' for certain block states



The v1.0.0 spec calls out PAYLOAD_BLOCK_ZERO FileOffsetMB field as being
'reserved'.  In practice, this means that Hyper-V will fail to read a
disk image with PAYLOAD_BLOCK_ZERO block states with a FileOffsetMB
value other than 0.

The other states that indicate a block that is not there
(PAYLOAD_BLOCK_UNDEFINED, PAYLOAD_BLOCK_NOT_PRESENT,
 PAYLOAD_BLOCK_UNMAPPED) have multiple options for what FileOffsetMB may
be set to, and '0' is explicitly called out as an option.

For all the above states, we will also just set the FileOffsetMB value
to 0.

Signed-off-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: a9fe92f53f07e6ab1693811e4312c0d1e958500b.1421787566.git.jcody@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

parent 9a29e18f

block/vhdx.c

+12 −1

Original line number	Diff line number	Diff line
		@@ -1174,7 +1174,18 @@ static void vhdx_update_bat_table_entry(BlockDriverState bs, BDRVVHDXState s,
		{
		/* The BAT entry is a uint64, with 44 bits for the file offset in units of
		* 1MB, and 3 bits for the block state. */
		if ((state == PAYLOAD_BLOCK_ZERO) \|\|
		(state == PAYLOAD_BLOCK_UNDEFINED) \|\|
		(state == PAYLOAD_BLOCK_NOT_PRESENT) \|\|
		(state == PAYLOAD_BLOCK_UNMAPPED)) {
		s->bat[sinfo->bat_idx] = 0; /* For PAYLOAD_BLOCK_ZERO, the
		FileOffsetMB field is denoted as
		'reserved' in the v1.0 spec. If it is
		non-zero, MS Hyper-V will fail to read
		the disk image */
		} else {
		s->bat[sinfo->bat_idx] = sinfo->file_offset;
		}

		s->bat[sinfo->bat_idx] \|= state & VHDX_BAT_STATE_BIT_MASK;