[v2] qemu-img: Document --force-share / -U

Message ID 20171208014456.16635-1-famz@redhat.com
State New
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  • [v2] qemu-img: Document --force-share / -U
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Commit Message

Fam Zheng Dec. 8, 2017, 1:44 a.m.
Signed-off-by: Fam Zheng <famz@redhat.com>

---
v2: - "code{qemu-img}". [Kashyap, Eric]
    - "etc.." -> "etc.".
---
 qemu-img.texi | 9 +++++++++
 1 file changed, 9 insertions(+)

Comments

Stefan Hajnoczi Dec. 8, 2017, 9:54 a.m. | #1
On Fri, Dec 08, 2017 at 09:44:56AM +0800, Fam Zheng wrote:
> +@item --force-share (-U)
> +
> +If specified, @code{qemu-img} will open the image with shared permissions,
> +which makes it less likely to conflict with a running guest's permissions due
> +to image locking. For example, this can be used to get the image information
> +(with 'info' subcommand) when the image is used by a running guest. Note that
> +this could produce inconsistent result because of concurrent metadata changes,
> +etc.

The documentation isn't clear on whether read-write is supported or just
read-only.

Also, should it be declared a legacy option right away to discourage
use in new software?
Kevin Wolf Dec. 8, 2017, 11:47 a.m. | #2
Am 08.12.2017 um 10:54 hat Stefan Hajnoczi geschrieben:
> On Fri, Dec 08, 2017 at 09:44:56AM +0800, Fam Zheng wrote:
> > +@item --force-share (-U)
> > +
> > +If specified, @code{qemu-img} will open the image with shared permissions,
> > +which makes it less likely to conflict with a running guest's permissions due
> > +to image locking. For example, this can be used to get the image information
> > +(with 'info' subcommand) when the image is used by a running guest. Note that
> > +this could produce inconsistent result because of concurrent metadata changes,
> > +etc.
> 
> The documentation isn't clear on whether read-write is supported or just
> read-only.
> 
> Also, should it be declared a legacy option right away to discourage
> use in new software?

I don't think this is a legacy option. As long you know what you're
doing, using it is fine.

Kevin
Kashyap Chamarthy Dec. 11, 2017, 9:05 a.m. | #3
On Fri, Dec 08, 2017 at 09:44:56AM +0800, Fam Zheng wrote:
> Signed-off-by: Fam Zheng <famz@redhat.com>
> 
> ---
> v2: - "code{qemu-img}". [Kashyap, Eric]
>     - "etc.." -> "etc.".
> ---
>  qemu-img.texi | 9 +++++++++
>  1 file changed, 9 insertions(+)

Reviewed-by: Kashyap Chamarthy <kchamart@redhat.com>

[...]
Fam Zheng Dec. 11, 2017, 9:30 a.m. | #4
On Fri, 12/08 09:54, Stefan Hajnoczi wrote:
> On Fri, Dec 08, 2017 at 09:44:56AM +0800, Fam Zheng wrote:
> > +@item --force-share (-U)
> > +
> > +If specified, @code{qemu-img} will open the image with shared permissions,
> > +which makes it less likely to conflict with a running guest's permissions due
> > +to image locking. For example, this can be used to get the image information
> > +(with 'info' subcommand) when the image is used by a running guest. Note that
> > +this could produce inconsistent result because of concurrent metadata changes,
> > +etc.
> 
> The documentation isn't clear on whether read-write is supported or just
> read-only.

block.c will emit an error if used with read-write. I will add a sentence for
that.

Fam

Patch

diff --git a/qemu-img.texi b/qemu-img.texi
index fdcf120f36..6b9f9adfc8 100644
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -57,6 +57,15 @@  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.
 
+@item --force-share (-U)
+
+If specified, @code{qemu-img} will open the image with shared permissions,
+which makes it less likely to conflict with a running guest's permissions due
+to image locking. For example, this can be used to get the image information
+(with 'info' subcommand) when the image is used by a running guest. Note that
+this could produce inconsistent result because of concurrent metadata changes,
+etc.
+
 @item fmt
 is the disk image format. It is guessed automatically in most cases. See below
 for a description of the supported disk formats.