Re: [Qemu-devel] [PATCH v6 02/22] qapi: Add lock-mode in blockdev-add options

[Fam Zheng <famz@redhat.com>]

On Fri, 06/17 11:17, Kevin Wolf wrote:
> Am 03.06.2016 um 10:48 hat Fam Zheng geschrieben:
> > To allow overriding the default locking behavior when opening the image.
> > 
> > Signed-off-by: Fam Zheng <famz@redhat.com>
> > ---
> >  qapi/block-core.json | 19 ++++++++++++++++++-
> >  1 file changed, 18 insertions(+), 1 deletion(-)
> > 
> > diff --git a/qapi/block-core.json b/qapi/block-core.json
> > index 98a20d2..23ec31d 100644
> > --- a/qapi/block-core.json
> > +++ b/qapi/block-core.json
> > @@ -2032,6 +2032,20 @@
> >              '*read-pattern': 'QuorumReadPattern' } }
> >  
> >  ##
> > +# @BlockdevLockMode
> > +#
> > +# Describes how QEMU should lock the image.
> > +#
> > +# @off:       Disabled
> > +# @shared:    Use shared lock for both RO and RW images.
> > +# @exclusive: Use exclusive lock for RW images, and shared lock for RO images.
> 
> This feels odd. If I request 'exclusive', I want to have exclusive.
> Reasons may include that I anticipate reopening the image r/w later for
> a commit operation and don't want to have this blocked by other readers.
> 
> I see where you're coming from, though, because this might not be a good
> default. Perhaps we need to have both then, an 'exclusive' option that
> does what it promises and a 'default' option that infers the wanted
> locking mode from the writability of the image.

Fair enough, though I'd call it "auto" instead of "default", what do you think?

Fam