[Xen-devel] [RFC QEMU PATCH 6/8] hostmem: add a host memory backend for Xen

[Haozhong Zhang <haozhong.zhang@xxxxxxxxx>]

Some virtual devices (e.g. NVDIMM) use the host memory backend to map
its backend resources to the guest. When those devices are used on Xen,
the mapping has to be managed out of QEMU. In order to reuse other parts
of the implementation of those devices, we introduce a host memory
backend for Xen (memory-backend-xen) which plays as a placeholder and
does not map any backend resource. Therefore, those devices when used on
Xen just needs to use the new backend.

Following is an example of the command options of an NVDIMM device using
a file backend on Xen:
   -object memory-backend-xen,id=mem1,mem-path=$FILENAME,size=$SIZE
   -device nvdimm,id=nvdimm1,memdev=mem1

Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
---
Cc: Eduardo Habkost <ehabkost@xxxxxxxxxx>
Cc: Igor Mammedov <imammedo@xxxxxxxxxx>
---
 backends/Makefile.objs |   1 +
 backends/hostmem-xen.c | 120 +++++++++++++++++++++++++++++++++++++++++++++++++
 backends/hostmem.c     |   9 ++++
 3 files changed, 130 insertions(+)
 create mode 100644 backends/hostmem-xen.c

diff --git a/backends/Makefile.objs b/backends/Makefile.objs
index 31a3a89..a587aca 100644
--- a/backends/Makefile.objs
+++ b/backends/Makefile.objs
@@ -9,3 +9,4 @@ common-obj-$(CONFIG_TPM) += tpm.o
 
 common-obj-y += hostmem.o hostmem-ram.o
 common-obj-$(CONFIG_LINUX) += hostmem-file.o
+common-obj-${CONFIG_XEN_BACKEND} += hostmem-xen.o
diff --git a/backends/hostmem-xen.c b/backends/hostmem-xen.c
new file mode 100644
index 0000000..144feee
--- /dev/null
+++ b/backends/hostmem-xen.c
@@ -0,0 +1,120 @@
+/*
+ * QEMU Host Memory Backend for Xen
+ *
+ * Copyright(C) 2016 Intel Corporation.
+ *
+ * Author:
+ *  Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/mmap-alloc.h"
+#include "sysemu/hostmem.h"
+#include "qapi/error.h"
+#include "qom/object_interfaces.h"
+
+#define TYPE_MEMORY_BACKEND_XEN "memory-backend-xen"
+
+#define MEMORY_BACKEND_XEN(obj) \
+    OBJECT_CHECK(HostMemoryBackendXen, (obj), TYPE_MEMORY_BACKEND_XEN)
+
+typedef struct HostMemoryBackendXen HostMemoryBackendXen;
+
+struct HostMemoryBackendXen {
+    HostMemoryBackend parent_obj;
+
+    char *mem_path;
+};
+
+static void xen_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
+{
+    HostMemoryBackendXen *db = MEMORY_BACKEND_XEN(backend);
+    int fd;
+    size_t page_size;
+
+    if (!backend->size) {
+        error_setg(errp, "can't create backend with size 0");
+        return;
+    }
+    memory_region_init(&backend->mr,
+                       OBJECT(backend), db->mem_path, backend->size);
+
+    fd = open(db->mem_path, O_RDONLY);
+    if (!fd) {
+        error_setg(errp, "can't open file %s, err %d", db->mem_path, errno);
+        return;
+    }
+    page_size = qemu_fd_getpagesize(fd);
+    backend->mr.align = MAX(page_size, QEMU_VMALLOC_ALIGN);
+    close(fd);
+}
+
+static void xen_backend_class_init(ObjectClass *oc, void *data)
+{
+    HostMemoryBackendClass *bc = MEMORY_BACKEND_CLASS(oc);
+
+    bc->alloc = xen_backend_memory_alloc;
+}
+
+static char *get_mem_path(Object *o, Error **errp)
+{
+    HostMemoryBackendXen *db = MEMORY_BACKEND_XEN(o);
+
+    return g_strdup(db->mem_path);
+}
+
+static void set_mem_path(Object *o, const char *str, Error **errp)
+{
+    HostMemoryBackend *backend = MEMORY_BACKEND(o);
+    HostMemoryBackendXen *db = MEMORY_BACKEND_XEN(o);
+
+    if (memory_region_size(&backend->mr)) {
+        error_setg(errp, "cannot change property value");
+        return;
+    }
+    g_free(db->mem_path);
+    db->mem_path = g_strdup(str);
+}
+
+static void
+xen_backend_instance_init(Object *o)
+{
+    object_property_add_str(o, "mem-path", get_mem_path,
+                            set_mem_path, NULL);
+}
+
+static void xen_backend_instance_finalize(Object *o)
+{
+    HostMemoryBackendXen *db = MEMORY_BACKEND_XEN(o);
+
+    g_free(db->mem_path);
+}
+
+static const TypeInfo xen_backend_info = {
+    .name = TYPE_MEMORY_BACKEND_XEN,
+    .parent = TYPE_MEMORY_BACKEND,
+    .class_init = xen_backend_class_init,
+    .instance_init = xen_backend_instance_init,
+    .instance_finalize = xen_backend_instance_finalize,
+    .instance_size = sizeof(HostMemoryBackendXen),
+};
+
+static void register_types(void)
+{
+    type_register_static(&xen_backend_info);
+}
+
+type_init(register_types);
diff --git a/backends/hostmem.c b/backends/hostmem.c
index b7a208d..75a969d 100644
--- a/backends/hostmem.c
+++ b/backends/hostmem.c
@@ -27,6 +27,8 @@ QEMU_BUILD_BUG_ON(HOST_MEM_POLICY_BIND != MPOL_BIND);
 QEMU_BUILD_BUG_ON(HOST_MEM_POLICY_INTERLEAVE != MPOL_INTERLEAVE);
 #endif
 
+#include "hw/xen/xen.h"
+
 static void
 host_memory_backend_get_size(Object *obj, Visitor *v, const char *name,
                              void *opaque, Error **errp)
@@ -294,6 +296,13 @@ host_memory_backend_memory_complete(UserCreatable *uc, 
Error **errp)
             goto out;
         }
 
+        /* The backend storage of MEMORY_BACKEND_XEN is managed by Xen,
+         * so no further work in this function is needed.
+         */
+        if (xen_enabled() && !backend->mr.ram_block) {
+            goto out;
+        }
+
         ptr = memory_region_get_ram_ptr(&backend->mr);
         sz = memory_region_size(&backend->mr);
 
-- 
2.10.1


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