Re: [Qemu-devel] [PATCH V5 01/10] specs/qcow2: add compress format extension

[Eric Blake]

On 07/25/2017 09:41 AM, Peter Lieven wrote:
> Signed-off-by: Peter Lieven <address@hidden>
> ---
>  docs/interop/qcow2.txt | 51 
> +++++++++++++++++++++++++++++++++++++++++++++++++-
>  roms/ipxe              |  2 +-
>  2 files changed, 51 insertions(+), 2 deletions(-)
> 

> +
> +== Compress format extension ==
> +
> +The compress format extension is an optional header extension. It provides
> +the ability to specify the compress algorithm and compress parameters

s/the compress algorithm/the compression algorithm/

> +that are used for compressed clusters. This new header MUST be present if
> +the incompatible-feature bit "compress format bit" is set and MUST be absent
> +otherwise.
> +
> +The fields of the compress format extension are:
> +
> +    Byte  0 - 13:  compress_format_name (padded with zeros, but not
> +                   necessarily null terminated if it has full length).
> +                   Valid compression format names currently are:
> +
> +                   deflate: Standard zlib deflate compression without
> +                            compression header

Why did you name it "deflate" instead of "zlib" again?

> +
> +              14:  compress_level (uint8_t)
> +
> +                   0 = default compress level (valid for all formats, 
> default)
> +
> +                   Additional valid compression levels for deflate 
> compression:
> +
> +                   All values between 1 and 9. 1 gives best speed, 9 gives 
> best
> +                   compression. The default compression level is defined by 
> zlib
> +                   and currently defaults to 6.
> +
> +              15:  compress_window_size (uint8_t)
> +
> +                   Window or dictionary size used by the compression format.
> +                   Currently only used by the deflate compression algorithm.

What must this be set to for other algorithms?  I guess we get to that
in later patches.

> +
> +                   Valid window sizes for deflate compression range from 8 to
> +                   15 inclusively.
> +
> +Note: Omitting the incompatible "Compress format bit" results in the usage
> +of deflate compression with default compression level and a window size of 12
> +(which was default before QEMU 2.11). If exactly these parameters are choosen

s/choosen/chosen,/

> +it is free to the implementation to omit the "Compress format bit" and the

s/it is free to the implementation to omit/the implementation may omit/

> +compress format extension when updating the QCOW2 header.
> +
> +
>  == Host cluster management ==
>  
>  qcow2 manages the allocation of host clusters by maintaining a reference 
> count
> diff --git a/roms/ipxe b/roms/ipxe
> index 0600d3a..b991c67 160000
> --- a/roms/ipxe
> +++ b/roms/ipxe
> @@ -1 +1 @@
> -Subproject commit 0600d3ae94f93efd10fc6b3c7420a9557a3a1670
> +Subproject commit b991c67c1d91574ef22336cc3a5944d1e63230c9

Oops.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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