Re: [PATCH v6 10/15] hostmem: Wire up RAM_NORESERVE via "reserve" property

[David Hildenbrand]

On 23.04.21 14:10, Markus Armbruster wrote:
> David Hildenbrand <david@redhat.com> writes:
>
> > > > diff --git a/backends/hostmem.c b/backends/hostmem.c
> > > > index c6c1ff5b99..58fdc1b658 100644
> > > > --- a/backends/hostmem.c
> > > > +++ b/backends/hostmem.c
> > > > @@ -217,6 +217,11 @@ static void host_memory_backend_set_prealloc(Object *obj, 
> > > > bool value,
> > > >        Error *local_err = NULL;
> > > >        HostMemoryBackend *backend = MEMORY_BACKEND(obj);
> > > >    +    if (!backend->reserve && value) {
> > > > +        error_setg(errp, "'prealloc=on' and 'reserve=off' are incompatible");
> > > > +        return;
> > > > +    }
> > >
> > > Aha.  Shouldn't this be documented in qom.json?
> >
> > Whoops, skipped that comment. Can add it if that's the place to
> > document that.
>
> Yes, please.  .json doc comments is where we document the external
> interface.

What about something like this:

diff --git a/qapi/qom.json b/qapi/qom.json
index e9b86893a5..4fa3137aab 100644
--- a/qapi/qom.json
+++ b/qapi/qom.json
@@ -559,6 +559,12 @@
 #                                        false generally, but true for machine
 #                                        types <= 4.0)
 #
+# Note: prealloc=true and reserve=false cannot be set at the same time. With
+#       reserve=true, the behavior depends on the operating system: for 
example,
+#       Linux will not reserve swap space for shared file mappings --
+#       "not applicable". In contrast, reserve=false will bail out if it cannot
+#       be configured accordingly.
+#
 # Since: 2.1
 ##
 { 'struct': 'MemoryBackendProperties',


--
Thanks,

David / dhildenb