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

[David Hildenbrand <david@redhat.com>]

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