Re: [Qemu-block] [PATCH v3] specs/qcow2: Fix documentation of the compressed cluster descriptor

[Kevin Wolf]

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.

Kevin