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Re: [Qemu-block] [PATCH v6 2/2] qemu-img: Document --force-share / -U

From: Eric Blake
Subject: Re: [Qemu-block] [PATCH v6 2/2] qemu-img: Document --force-share / -U
Date: Tue, 30 Jan 2018 08:23:50 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2

On 01/30/2018 12:34 AM, Fam Zheng wrote:
> Signed-off-by: Fam Zheng <address@hidden>
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
>  qemu-img.texi | 7 +++++++
>  1 file changed, 7 insertions(+)
> diff --git a/qemu-img.texi b/qemu-img.texi
> index 60a0e080c6..ec7e2f5d1e 100644
> --- a/qemu-img.texi
> +++ b/qemu-img.texi
> @@ -86,6 +86,13 @@ exclusive with the @var{-O} parameters. It is currently 
> required to also use
>  the @var{-n} parameter to skip image creation. This restriction may be 
> relaxed
>  in a future release.
> address@hidden --force-share (-U)
> +If specified, @code{qemu-img} will open the image in shared mode, allowing
> +concurrent writers. For example, this can be used to get the image 
> information

Actually, we only permit one writer at a time.  Would it be better to
say "allowing a concurrent writer"?

> +(with 'info' subcommand) when the image is used by a running guest.  Note 
> that
> +this could produce inconsistent results because of concurrent metadata 
> changes,
> +etc. This option is only allowed when opening images in read-only mode.

After all, we are stating that this process (which must be read-only,
because we can't have two writers at once) is permitting some other
process to be the concurrent writer (but not multiple processes to be
concurrent writers)

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

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