[libvirt] [PATCH 2/2] Add -mem-shared option

[Eduardo Habkost]

+Markus

On Tue, Dec 03, 2019 at 03:43:03PM +0100, Igor Mammedov wrote:
> On Tue, 3 Dec 2019 09:56:15 +0100
> Thomas Huth <thuth at redhat.com> wrote:
> 
> > On 02/12/2019 22.00, Eduardo Habkost wrote:
> > > On Mon, Dec 02, 2019 at 08:39:48AM +0100, Igor Mammedov wrote:  
> > >> On Fri, 29 Nov 2019 18:46:12 +0100
> > >> Paolo Bonzini <pbonzini at redhat.com> wrote:
> > >>  
> > >>> On 29/11/19 13:16, Igor Mammedov wrote:  
> > >>>> As for "-m", I'd make it just an alias that translates
> > >>>>  -m/mem-path/mem-prealloc    
> > >>>
> > >>> I think we should just deprecate -mem-path/-mem-prealloc in 5.0.  CCing
> > >>> Thomas as mister deprecation. :)  
> > >>
> > >> I'll add that to my series  
> > > 
> > > Considering that the plan is to eventually reimplement those
> > > options as syntactic sugar for memory backend options (hopefully
> > > in less than 2 QEMU releases), what's the point of deprecating
> > > them?  
> > 
> > Well, it depends on the "classification" [1] of the parameter...
> > 
> > Let's ask: What's the main purpose of the option?
> > 
> > Is it easier to use than the "full" option, and thus likely to be used
> > by a lot of people who run QEMU directly from the CLI? In that case it
> > should stay as "convenience option" and not be deprecated.
> > 
> > Or is the option merely there to give the upper layers like libvirt or
> > some few users and their scripts some more grace period to adapt their
> > code, but we all agree that the options are rather ugly and should
> > finally go away? Then it's rather a "legacy option" and the deprecation
> > process is the right way to go. Our QEMU interface is still way 
> > overcrowded, we should try to keep it as clean as possible.
> 
> After switching to memdev for main RAM, users could use relatively
> short global options
>  -global memory-backend.prealloc|share=on
> and
>  -global memory-backend-file.mem-path=X|prealloc|share=on
> 
> instead of us adding and maintaining slightly shorter
>  -mem-shared/-mem-path/-mem-prealloc

Global properties are a convenient way to expose knobs through
the command line with little effort, but we have no documentation
on which QOM properties are really supposed to be touched by
users using -global.

Unless we fix the lack of documentation, I'd prefer to have
syntactic sugar translated to -global instead of recommending
direct usage of -global.

-- 
Eduardo