[PULL 3/3] hostmem: Don't report pmem attribute if unsupported

[Eduardo Habkost]

From: Michal Privoznik <mprivozn@redhat.com>

When management applications (like Libvirt) want to check whether
memory-backend-file.pmem is supported they can list object
properties using 'qom-list-properties'. However, 'pmem' is
declared always (and thus reported always) and only at runtime
QEMU errors out if it was built without libpmem (and thus can not
guarantee write persistence). This is suboptimal since we have
ability to declare attributes at compile time.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Tested-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1915216
Message-Id: 
<dfcc5dc7e2efc0283bc38e3036da2c0323621cdb.1611647111.git.mprivozn@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 backends/hostmem-file.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index 733408e076f..b683da9daf8 100644
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -124,6 +124,7 @@ static void file_memory_backend_set_align(Object *o, 
Visitor *v,
     fb->align = val;
 }
 
+#ifdef CONFIG_LIBPMEM
 static bool file_memory_backend_get_pmem(Object *o, Error **errp)
 {
     return MEMORY_BACKEND_FILE(o)->is_pmem;
@@ -140,17 +141,9 @@ static void file_memory_backend_set_pmem(Object *o, bool 
value, Error **errp)
         return;
     }
 
-#ifndef CONFIG_LIBPMEM
-    if (value) {
-        error_setg(errp, "Lack of libpmem support while setting the 'pmem=on'"
-                   " of %s. We can't ensure data persistence.",
-                   object_get_typename(o));
-        return;
-    }
-#endif
-
     fb->is_pmem = value;
 }
+#endif /* CONFIG_LIBPMEM */
 
 static bool file_memory_backend_get_readonly(Object *obj, Error **errp)
 {
@@ -203,8 +196,10 @@ file_backend_class_init(ObjectClass *oc, void *data)
         file_memory_backend_get_align,
         file_memory_backend_set_align,
         NULL, NULL);
+#ifdef CONFIG_LIBPMEM
     object_class_property_add_bool(oc, "pmem",
         file_memory_backend_get_pmem, file_memory_backend_set_pmem);
+#endif
     object_class_property_add_bool(oc, "readonly",
         file_memory_backend_get_readonly,
         file_memory_backend_set_readonly);
-- 
2.28.0