Re: [PATCH v3] machine: add missing doc for memory-backend option

[Daniel P . Berrangé]

On Wed, Jan 27, 2021 at 04:35:22PM +0100, Igor Mammedov wrote:
> On Wed, 27 Jan 2021 15:24:26 +0100
> Michal Privoznik <mprivozn@redhat.com> wrote:
> 
> > On 1/27/21 11:54 AM, Daniel P. Berrangé wrote:
> > > On Wed, Jan 27, 2021 at 10:45:11AM +0000, Daniel P. Berrangé wrote:  
> > >> On Thu, Jan 21, 2021 at 11:15:04AM -0500, Igor Mammedov wrote:  
> > 
> > 
> > >>
> > >> How does a mgmt app know which machine types need to use this
> > >> option ? The machine type names are opaque strings, and apps
> > >> must not attempt to parse or interpret the version number
> > >> inside the machine type name, as they can be changed by
> > >> distros.  IOW, saying to use it for machine types 4.0 and
> > >> older isn't a valid usage strategy IMHO.
> it's possible (but no necessary) to use knob with new machine types
> (defaults for these match suggested property value).

IIUC, this means that setting the property has no impact on
migration ABI for new machine types > 4.0....

> Limiting knob usage to 4.0 and older would allow us to drop
> without extra efforts once 4.0 is deprecated/removed.

...so, even if we set the property unconditionally for *all*
machine types, then we can still remove it in future, becuase
its removal won't affect ABI of the 5.x, 6.x machine types.


Regards,
Daniel
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