Re: [Qemu-devel] [PATCH] [RFC] qcow2: add compression type feature

[Max Reitz <mreitz@redhat.com>]

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On 05.02.19 10:08, Denis Plotnikov wrote:
> The patch adds some preparation parts for incompatible compression type
> feature into QCOW2 header that indicates that *all* compressed clusters
> must be (de)compressed using a certain compression type.
> 
> It is implied that the compression type is set on the image creation and
> can be changed only later by image convertion, thus the only compression
> algorithm is used for the image.
> 
> The plan is to add support for ZSTD and then may be something more effective
> in the future.
> 
> ZSDT compression algorithm consumes 3-5 times less CPU power with a
> comparable comression ratio with zlib. It would be wise to use it for
> data compression f.e. for backups.
> 
> The default compression is ZLIB.
> 
> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
> ---
>  block/qcow2.c | 25 +++++++++++++++++++++++++
>  block/qcow2.h | 26 ++++++++++++++++++++++----
>  2 files changed, 47 insertions(+), 4 deletions(-)

Are there plans to pursue this further?

[...]

> diff --git a/block/qcow2.h b/block/qcow2.h
> index 32cce9eee2..fdde5bbefd 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -112,6 +112,10 @@
>  #define QCOW2_OPT_REFCOUNT_CACHE_SIZE "refcount-cache-size"
>  #define QCOW2_OPT_CACHE_CLEAN_INTERVAL "cache-clean-interval"
>  
> +/* Compression types */
> +#define QCOW2_COMPRESSION_TYPE_ZLIB    0
> +#define QCOW2_COMPRESSION_TYPE_ZSTD    1

We probably want QAPI types anyway (qemu-img info should report the
compression type), so I think we could use them instead.

>  typedef struct QCowHeader {
>      uint32_t magic;
>      uint32_t version;
> @@ -197,10 +201,13 @@ enum {
>  
>  /* Incompatible feature bits */
>  enum {
> -    QCOW2_INCOMPAT_DIRTY_BITNR   = 0,
> -    QCOW2_INCOMPAT_CORRUPT_BITNR = 1,
> -    QCOW2_INCOMPAT_DIRTY         = 1 << QCOW2_INCOMPAT_DIRTY_BITNR,
> -    QCOW2_INCOMPAT_CORRUPT       = 1 << QCOW2_INCOMPAT_CORRUPT_BITNR,
> +    QCOW2_INCOMPAT_DIRTY_BITNR            = 0,
> +    QCOW2_INCOMPAT_CORRUPT_BITNR          = 1,
> +    QCOW2_INCOMPAT_COMPRESSION_TYPE_BITNR = 2,
> +    QCOW2_INCOMPAT_DIRTY                  = 1 << QCOW2_INCOMPAT_DIRTY_BITNR,
> +    QCOW2_INCOMPAT_CORRUPT                = 1 << QCOW2_INCOMPAT_CORRUPT_BITNR,
> +    QCOW2_INCOMPAT_COMPRESSION_TYPE       =
> +                                    1 << QCOW2_INCOMPAT_COMPRESSION_TYPE_BITNR,
>  
>      QCOW2_INCOMPAT_MASK          = QCOW2_INCOMPAT_DIRTY
>                                   | QCOW2_INCOMPAT_CORRUPT,

This mask needs to be expanded by QCOW2_INCOMPAT_COMPRESSION_TYPE.

> @@ -256,6 +263,10 @@ typedef struct Qcow2BitmapHeaderExt {
>      uint64_t bitmap_directory_offset;
>  } QEMU_PACKED Qcow2BitmapHeaderExt;
>  
> +typedef struct Qcow2CompressionTypeExt {
> +    uint32_t compression_type;
> +} QEMU_PACKED Qcow2CompressionTypeExt;
> +
>  typedef struct BDRVQcow2State {
>      int cluster_bits;
>      int cluster_size;
> @@ -340,6 +351,13 @@ typedef struct BDRVQcow2State {
>  
>      CoQueue compress_wait_queue;
>      int nb_compress_threads;
> +    /**
> +     * Compression type used for the image. Default: 0 - ZLIB
> +     * The image compression type is set on image creation.
> +     * The only way to change the compression type is to convert the image
> +     * with the desired compresion type set

*compression

And, well, ideally qemu-img amend could perform this operation, too.

Max

> +     */
> +    uint32_t compression_type;
>  } BDRVQcow2State;
>  
>  typedef struct Qcow2COWRegion {
> 



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