hostmem: use object id for memory region name with >= 4.0

hostmem-file and hostmem-memfd use the whole object path for the
memory region name, and hostname-ram uses only the path component (the
object id, or canonical path basename):

qemu -m 1024 -object memory-backend-file,id=mem,size=1G,mem-path=/tmp/foo -numa node,memdev=mem -monitor stdio
(qemu) info ramblock
              Block Name    PSize              Offset               Used              Total
            /objects/mem    4 KiB  0x0000000000000000 0x0000000040000000 0x0000000040000000

qemu -m 1024 -object memory-backend-memfd,id=mem,size=1G -numa node,memdev=mem -monitor stdio
(qemu) info ramblock
              Block Name    PSize              Offset               Used              Total
            /objects/mem    4 KiB  0x0000000000000000 0x0000000040000000 0x0000000040000000

qemu -m 1024 -object memory-backend-ram,id=mem,size=1G -numa node,memdev=mem -monitor stdio
(qemu) info ramblock
              Block Name    PSize              Offset               Used              Total
                     mem    4 KiB  0x0000000000000000 0x0000000040000000 0x0000000040000000

For consistency, change to use object id for -file and -memfd as well
with >= 4.0.

Having a consistent naming allows to migrate to different hostmem
backends.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Eduardo Habkost <ehabkost@redhat.com>

backends/hostmem-file.c

@@ -43,7 +43,7 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
 {
     HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(backend);
 #ifdef CONFIG_POSIX
-    gchar *path;
+    gchar *name;
 #endif
 
     if (!backend->size) {
@@ -58,14 +58,14 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
     error_setg(errp, "-mem-path not supported on this host");
 #else
     backend->force_prealloc = mem_prealloc;
-    path = object_get_canonical_path(OBJECT(backend));
+    name = host_memory_backend_get_name(backend);
     memory_region_init_ram_from_file(&backend->mr, OBJECT(backend),
-                                     path,
+                                     name,
                                      backend->size, fb->align,
                                      (backend->share ? RAM_SHARED : 0) |
                                      (fb->is_pmem ? RAM_PMEM : 0),
                                      fb->mem_path, errp);
-    g_free(path);
+    g_free(name);
 #endif
 }
 

backends/hostmem-memfd.c

@@ -53,7 +53,7 @@ memfd_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
         return;
     }
 
-    name = object_get_canonical_path(OBJECT(backend));
+    name = host_memory_backend_get_name(backend);
     memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend),
                                    name, backend->size,
                                    backend->share, fd, errp);

backends/hostmem-ram.c

@@ -16,21 +16,20 @@
 
 #define TYPE_MEMORY_BACKEND_RAM "memory-backend-ram"
 
-
 static void
 ram_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
 {
-    char *path;
+    char *name;
 
     if (!backend->size) {
         error_setg(errp, "can't create backend with size 0");
         return;
     }
 
-    path = object_get_canonical_path_component(OBJECT(backend));
+    name = host_memory_backend_get_name(backend);
-    memory_region_init_ram_shared_nomigrate(&backend->mr, OBJECT(backend), path,
+    memory_region_init_ram_shared_nomigrate(&backend->mr, OBJECT(backend), name,
                            backend->size, backend->share, errp);
-    g_free(path);
+    g_free(name);
 }
 
 static void

backends/hostmem.c

@@ -28,6 +28,16 @@ QEMU_BUILD_BUG_ON(HOST_MEM_POLICY_BIND != MPOL_BIND);
 QEMU_BUILD_BUG_ON(HOST_MEM_POLICY_INTERLEAVE != MPOL_INTERLEAVE);
 #endif
 
+char *
+host_memory_backend_get_name(HostMemoryBackend *backend)
+{
+    if (!backend->use_canonical_path) {
+        return object_get_canonical_path_component(OBJECT(backend));
+    }
+
+    return object_get_canonical_path(OBJECT(backend));
+}
+
 static void
 host_memory_backend_get_size(Object *obj, Visitor *v, const char *name,
                              void *opaque, Error **errp)
@@ -247,6 +257,11 @@ static void host_memory_backend_init(Object *obj)
     backend->prealloc = mem_prealloc;
 }
 
+static void host_memory_backend_post_init(Object *obj)
+{
+    object_apply_compat_props(obj);
+}
+
 bool host_memory_backend_mr_inited(HostMemoryBackend *backend)
 {
     /*
@@ -395,6 +410,23 @@ static void host_memory_backend_set_share(Object *o, bool value, Error **errp)
     backend->share = value;
 }
 
+static bool
+host_memory_backend_get_use_canonical_path(Object *obj, Error **errp)
+{
+    HostMemoryBackend *backend = MEMORY_BACKEND(obj);
+
+    return backend->use_canonical_path;
+}
+
+static void
+host_memory_backend_set_use_canonical_path(Object *obj, bool value,
+                                           Error **errp)
+{
+    HostMemoryBackend *backend = MEMORY_BACKEND(obj);
+
+    backend->use_canonical_path = value;
+}
+
 static void
 host_memory_backend_class_init(ObjectClass *oc, void *data)
 {
@@ -441,6 +473,9 @@ host_memory_backend_class_init(ObjectClass *oc, void *data)
         &error_abort);
     object_class_property_set_description(oc, "share",
         "Mark the memory as private to QEMU or shared", &error_abort);
+    object_class_property_add_bool(oc, "x-use-canonical-path-for-ramblock-id",
+        host_memory_backend_get_use_canonical_path,
+        host_memory_backend_set_use_canonical_path, &error_abort);
 }
 
 static const TypeInfo host_memory_backend_info = {
@@ -451,6 +486,7 @@ static const TypeInfo host_memory_backend_info = {
     .class_init = host_memory_backend_class_init,
     .instance_size = sizeof(HostMemoryBackend),
     .instance_init = host_memory_backend_init,
+    .instance_post_init = host_memory_backend_post_init,
     .interfaces = (InterfaceInfo[]) {
         { TYPE_USER_CREATABLE },
         { }

hw/core/machine.c

@@ -32,6 +32,14 @@ GlobalProperty hw_compat_3_1[] = {
         .driver   = "pcie-root-port",
         .property = "x-width",
         .value    = "1",
+    },{
+        .driver   = "memory-backend-file",
+        .property = "x-use-canonical-path-for-ramblock-id",
+        .value    = "true",
+    },{
+        .driver   = "memory-backend-memfd",
+        .property = "x-use-canonical-path-for-ramblock-id",
+        .value    = "true",
     },
 };
 const size_t hw_compat_3_1_len = G_N_ELEMENTS(hw_compat_3_1);

include/sysemu/hostmem.h

@@ -53,7 +53,7 @@ struct HostMemoryBackend {
 
     /* protected */
     uint64_t size;
-    bool merge, dump;
+    bool merge, dump, use_canonical_path;
     bool prealloc, force_prealloc, is_mapped, share;
     DECLARE_BITMAP(host_nodes, MAX_NODES + 1);
     HostMemPolicy policy;
@@ -67,5 +67,6 @@ MemoryRegion *host_memory_backend_get_memory(HostMemoryBackend *backend);
 void host_memory_backend_set_mapped(HostMemoryBackend *backend, bool mapped);
 bool host_memory_backend_is_mapped(HostMemoryBackend *backend);
 size_t host_memory_backend_pagesize(HostMemoryBackend *memdev);
+char *host_memory_backend_get_name(HostMemoryBackend *backend);
 
 #endif