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Re: [Qemu-block] [PATCH v7 3/6] qcow2: Reduce REFT_OFFSET_MASK
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-block] [PATCH v7 3/6] qcow2: Reduce REFT_OFFSET_MASK |
Date: |
Fri, 29 Jun 2018 10:44:44 +0200 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
Am 28.06.2018 um 21:07 hat Eric Blake geschrieben:
> Match our code to the spec change in the previous patch - there's
> no reason for the refcount table to allow larger offsets than the
> L1/L2 tables.
What about internal snapshots? And anyway, because of the metadata
overhead, the physical image size of a fully allocated image is always
going to be at least minimally larger than the virtual disk size.
I'm not necessarily opposed to making the change if there is a good
reason to make it, but I don't see a real need for it and the
justification used here and also in the previous patch is incorrect.
Kevin
> In practice, no image has more than 64PB of
> allocated clusters anyways, as anything beyond that can't be
> expressed via L2 mappings to host offsets.
>
> Suggested-by: Alberto Garcia <address@hidden>
> Signed-off-by: Eric Blake <address@hidden>
> Reviewed-by: Alberto Garcia <address@hidden>
>
> ---
> v4: new patch
> ---
> block/qcow2.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/block/qcow2.h b/block/qcow2.h
> index 01b5250415f..3774229ef9c 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -439,7 +439,7 @@ typedef enum QCow2MetadataOverlap {
> #define L2E_OFFSET_MASK 0x00fffffffffffe00ULL
> #define L2E_COMPRESSED_OFFSET_SIZE_MASK 0x3fffffffffffffffULL
>
> -#define REFT_OFFSET_MASK 0xfffffffffffffe00ULL
> +#define REFT_OFFSET_MASK 0x00fffffffffffe00ULL
>
> static inline int64_t start_of_cluster(BDRVQcow2State *s, int64_t offset)
> {
> --
> 2.14.4
>
- [Qemu-block] [PATCH v7 0/6] minor qcow2 compression improvements, Eric Blake, 2018/06/28
- [Qemu-block] [PATCH v7 4/6] qcow2: Don't allow overflow during cluster allocation, Eric Blake, 2018/06/28
- [Qemu-block] [PATCH v7 5/6] iotests: Add new test 220 for max compressed cluster offset, Eric Blake, 2018/06/28
- [Qemu-block] [PATCH v7 2/6] qcow2: Document some maximum size constraints, Eric Blake, 2018/06/28
- [Qemu-block] [PATCH v7 6/6] qcow2: Avoid memory over-allocation on compressed images, Eric Blake, 2018/06/28