[PATCH] virsh: Fix logic wrt to --current flag in cmdSetmem

[Peter Krempa]

On Tue, May 18, 2021 at 15:55:45 +0200, Pavel Hrdina wrote:
> On Tue, May 18, 2021 at 03:17:56PM +0200, Michal Prívozník wrote:
> > On 5/18/21 3:12 PM, Pavel Hrdina wrote:
> > > On Tue, May 18, 2021 at 03:02:55PM +0200, Ján Tomko wrote:
> > >> On a Tuesday in 2021, Michal Privoznik wrote:
> > >>> In my commit of v7.1.0-rc1~376 I've simplified the logic of
> > >>> handling @flags. My assumption back then was that calling
> > >>> virDomainSetMemory() is equivalent to
> > >>> virDomainSetMemoryFlags(flags = 0). But that is not the case,
> > >>> because it is equivalent to virDomainSetMemoryFlags(flags =
> > >>> VIR_DOMAIN_AFFECT_LIVE). Fix the condition that calls the old
> > >>> API.
> > >>>
> > >>> Fixes: b5e267e8c59a257652f88d034cb1e0ce1ed4b58a
> > >>
> > >> before that commit, if the user did not specify any of:
> > >>   config, live, current
> > >> we used the old API.
> > >>
> > >> After this change, the new API will be used for those cases.
> > > 
> > > The question is if we support using upstream virsh with old libvirt
> > > where only non-flags API is available. If not we should drop the
> > > non-flags API usage from virsh completely.
> > 
> > I think in general we do. In this specific case,
> > virDomainSetMemoryFlags() API was introduced in v0.9.0 release (which is
> > 10 years ago). And since we dropped RHEL-7 support recently and the
> > oldest QEMU we support is from late 2017 our attempt to be that
> > backwards compatible is questionable IMO.
> 
> Exactly my question. We have some support matrix where libvirt should be
> able to compile and run but there is no explicit support policy for
> using virsh with old libvirt or for obsolete APIs that should not be
> used. I would vote to use the same matrix as we already have.
> 
> That would allow us to remove probably all non-flags APIs from virsh
> code.

This fix, well a variation of it removing the old API would be the only
acceptable variant here.

The original code in virsh prior to the change would call the old API
also when no flag was used.

This patch is not really fixing the old behaviour though, because with
no flag you get the behavior of '--current' rather than the pre-existing
behavior of implying '--live'.

Thus we either declare that we do want to change the behaviour in virsh
and use it as an excuse to delete the use of the old api,

or

this patch needs to be fixed more to restore the logic,

or

just revert the original commit.

But this patch as-is is wrong and is not really fixing the behaviour
without adding more regression.