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Date: Thu, 27 Oct 2011 18:12:00 +0200
From: Stefan Weil <sw@weilnetz.de>
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Subject: Re: [Qemu-devel] [PATCH] Teach block/vdi about "discarded" (no
 longer allocated) blocks
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To: Kevin Wolf <kwolf@redhat.com>
Cc: qemu-trivial@nongnu.org, qemu-devel@nongnu.org, Eric Sunshine <sunshine@sunshineco.com>

Am 27.10.2011 10:53, schrieb Kevin Wolf:
> Am 26.10.2011 21:51, schrieb Eric Sunshine:
>> An entry in the VDI block map will hold an offset to the actual block if
>> the block is allocated, or one of two specially-interpreted values if
>> not allocated. Using VirtualBox terminology, value VDI_IMAGE_BLOCK_FREE
>> (0xffffffff) represents a never-allocated block (semantically arbitrary
>> content). VDI_IMAGE_BLOCK_ZERO (0xfffffffe) represents a "discarded"
>> block (semantically zero-filled). block/vdi knows only about
>> VDI_IMAGE_BLOCK_FREE. Teach it about VDI_IMAGE_BLOCK_ZERO.
>>
>> Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
>
> Thanks, applied to the block branch.
>
> Kevin


Kevin, I don't want to block improvements. Nevertheless
I'd like to see a small modification in this patch:
both #defines should be implemented without a type cast.
Please change them or wait until Eric sends an update.

My favorite is this:

#define VDI_UNALLOCATED UINT32_MAX
#define VDI_DISCARD     (VDI_UNALLOCATED - 1)

This would also be ok:

#define VDI_UNALLOCATED 0xffffffffU
#define VDI_DISCARD     0xfffffffeU

Using the macro names and the definitions (with type cast)
from the original VirtualBox code would also be ok.

Cheers,
Stefan