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Re: [Qemu-block] [PATCH v3] specs/qcow2: Fix documentation of the compre
Re: [Qemu-block] [PATCH v3] specs/qcow2: Fix documentation of the compressed cluster descriptor
Wed, 21 Feb 2018 18:08:35 +0100
Am 21.02.2018 um 15:08 hat Alberto Garcia geschrieben:
> This patch fixes several mistakes in the documentation of the
> compressed cluster descriptor:
> 1) the documentation claims that the cluster descriptor contains the
> number of sectors used to store the compressed data, but what it
> actually contains is the number of sectors *minus one* or, in other
> words, the number of additional sectors after the first one.
> 2) the width of the fields is incorrectly specified. The number of bits
> used by each field is
> x = 62 - (cluster_bits - 8) for the offset field
> y = (cluster_bits - 8) for the size field
> So the offset field's location is [0, x-1], not [0, x] as stated.
> 3) the size field does not contain the size of the compressed data,
> but rather the number of sectors where that data is stored. The
> compressed data starts at the exact point specified in the offset
> field and ends when there's enough data to produce a cluster of
> decompressed data. Both points can be in the middle of a sector,
> allowing several compressed clusters to be stored next to one
> another, sharing sectors if necessary.
> Signed-off-by: Alberto Garcia <address@hidden>
Thanks, applied to the block branch.