Re: [PULL 06/18] qemu-img: Add --target-is-zero to convert

[Eric Blake]

On 2/20/20 10:06 AM, Max Reitz wrote:
> From: David Edmondson <address@hidden>
>
> In many cases the target of a convert operation is a newly provisioned
> target that the user knows is blank (reads as zero). In this situation
> there is no requirement for qemu-img to wastefully zero out the entire
> device.
>
> Add a new option, --target-is-zero, allowing the user to indicate that
> an existing target device will return zeros for all reads.
>
> Signed-off-by: David Edmondson <address@hidden>
> Message-Id: <address@hidden>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> Reviewed-by: Eric Blake <address@hidden>
> Signed-off-by: Max Reitz <address@hidden>
> ---
>   docs/interop/qemu-img.rst |  9 ++++++++-
>   qemu-img-cmds.hx          |  4 ++--
>   qemu-img.c                | 26 +++++++++++++++++++++++---
>   3 files changed, 33 insertions(+), 6 deletions(-)
>
> diff --git a/docs/interop/qemu-img.rst b/docs/interop/qemu-img.rst
> index 42e4451db4..5f40137c10 100644
> --- a/docs/interop/qemu-img.rst
> +++ b/docs/interop/qemu-img.rst
> @@ -214,6 +214,13 @@ Parameters to convert subcommand:
>     will still be printed.  Areas that cannot be read from the source will be
>     treated as containing only zeroes.
>   
> +.. option:: --target-is-zero
> +
> +  Assume that reading the destination image will always return
> +  zeros. This parameter is mutually exclusive with a destination image

Late tweak now that this is in a pull request, so we may want a followup 
patch, but:

The image doesn't always return zeros after we write to it, maybe we 
should tweak this sentence:

Assume that reading the destination image will initially return all zeros.

Also, my earlier comment about 'zeroes' one line before 'zeros' still 
applies - although both spellings are valid, we look inconsistent when 
we can't make up our mind within two adjacent paragraphs.

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