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Re: [Qemu-block] [Qemu-devel] [PATCH v2 18/32] qcow2: Update qcow2_get_c

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v2 18/32] qcow2: Update qcow2_get_cluster_offset() to support L2 slices
Date: Tue, 16 Jan 2018 16:42:45 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2

On 12/15/2017 06:53 AM, Alberto Garcia wrote:
> qcow2_get_cluster_offset() checks how many contiguous bytes are
> available at a given offset. The returned number of bytes is limited
> by the amount that can be addressed without having to load more than
> one L2 table.
> Since we'll be loading L2 slices instead of full tables this patch
> changes the limit accordingly using the size of the L2 slice for the
> calculations instead of the full table size.
> The l2_table variable is also renamed to l2_slice to reflect this, and
> offset_to_l2_index() is replaced with offset_to_l2_slice_index().
> Signed-off-by: Alberto Garcia <address@hidden>
> ---
>  block/qcow2-cluster.c | 30 +++++++++++++++---------------
>  1 file changed, 15 insertions(+), 15 deletions(-)

Callers like 'qemu-img map' will potentially have to iterate in more
steps over an entire image; but that's not a severe limitation.  The
block_status() functions already document that as long as drivers make
progress, callers must be prepared for back-to-back calls that return
the same status, so you are not breaking semantics with a shorter
clamping limit.

Maybe some of that is worth mentioning in the commit message.  Either way,

Reviewed-by: Eric Blake <address@hidden>

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

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