Re: [PATCH v4 28/30] qcow2: Add the 'extended_l2' option and the QCOW2_INCOMPAT_EXTL2 bit

[Eric Blake <eblake@redhat.com>]

On 3/17/20 1:16 PM, Alberto Garcia wrote:
> Now that the implementation of subclusters is complete we can finally
> add the necessary options to create and read images with this feature,
> which we call "extended L2 entries".
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> Reviewed-by: Max Reitz <mreitz@redhat.com>
> ---

> +++ b/qapi/block-core.json
> @@ -66,6 +66,9 @@
>   #                 standalone (read-only) raw image without looking at qcow2
>   #                 metadata (since: 4.0)
>   #
> +# @extended-l2: true if the image has extended L2 entries; only valid for
> +#               compat >= 1.1 (since 5.0)

Looks like we'll have to tweak this to 5.1 now (multiple spots).

> +++ b/block/qcow2.h
> @@ -231,13 +231,16 @@ enum {
>       QCOW2_INCOMPAT_DIRTY_BITNR      = 0,
>       QCOW2_INCOMPAT_CORRUPT_BITNR    = 1,
>       QCOW2_INCOMPAT_DATA_FILE_BITNR  = 2,
> +    QCOW2_INCOMPAT_EXTL2_BITNR      = 4,

Why are we skipping bit 3?  (Hmm, now I have to go find the earlier 
patch that touched the spec...)

aha - the spec documented compression bits (the spec change for those 
made 5.0, but the qcow2 implementation did not); we'll have to rebase 
depending on what lands first.  But the resolution of that merge 
conflict will result in both feature bits eventually existing here.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org