[Qemu-devel] [RFC PATCH 2/4] nvdimm: add functions to initialize and perform flush on back store

[Haozhong Zhang]

fsync() is used to persist modifications to the back store. If the
host NVDIMM is used as the back store, fsync() on Linux will trigger
the write to the host flush hint address.

Signed-off-by: Haozhong Zhang <address@hidden>
---
 hw/mem/nvdimm.c         | 22 ++++++++++++++++++++++
 include/hw/mem/nvdimm.h | 13 +++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/hw/mem/nvdimm.c b/hw/mem/nvdimm.c
index db896b0..484ab8b 100644
--- a/hw/mem/nvdimm.c
+++ b/hw/mem/nvdimm.c
@@ -78,6 +78,26 @@ static MemoryRegion *nvdimm_get_memory_region(PCDIMMDevice 
*dimm)
     return &nvdimm->nvdimm_mr;
 }
 
+static void nvdimm_flush_init(NVDIMMDevice *nvdimm, MemoryRegion *hostmem_mr)
+{
+    if (nvdimm->flush_hint_enabled) {
+        nvdimm->backend_fd = memory_region_get_fd(hostmem_mr);
+    } else {
+        nvdimm->backend_fd = -1;
+    }
+}
+
+void nvdimm_flush(NVDIMMDevice *nvdimm)
+{
+    if (nvdimm->backend_fd != -1) {
+        /*
+         * If the backend store is a physical NVDIMM device, fsync()
+         * will trigger the flush via the flush hint on the host device.
+         */
+        fsync(nvdimm->backend_fd);
+    }
+}
+
 static void nvdimm_realize(PCDIMMDevice *dimm, Error **errp)
 {
     MemoryRegion *mr = host_memory_backend_get_memory(dimm->hostmem, errp);
@@ -105,6 +125,8 @@ static void nvdimm_realize(PCDIMMDevice *dimm, Error **errp)
     memory_region_init_alias(&nvdimm->nvdimm_mr, OBJECT(dimm),
                              "nvdimm-memory", mr, 0, pmem_size);
     nvdimm->nvdimm_mr.align = align;
+
+    nvdimm_flush_init(nvdimm, mr);
 }
 
 /*
diff --git a/include/hw/mem/nvdimm.h b/include/hw/mem/nvdimm.h
index 03e1ff9..eb71f41 100644
--- a/include/hw/mem/nvdimm.h
+++ b/include/hw/mem/nvdimm.h
@@ -71,6 +71,18 @@ struct NVDIMMDevice {
      * guest via ACPI NFIT and _FIT method if NVDIMM hotplug is supported.
      */
     MemoryRegion nvdimm_mr;
+
+    /*
+     * If true, a flush hint address structure will be built for this
+     * NVDIMM device.
+     */
+    bool flush_hint_enabled;
+    /*
+     * File descriptor of the backend store, which is used in nvdimm
+     * flush.  It's cached in NVDIMMDevice rather than being fetched
+     * at each request in order to accelerate the flush a little bit.
+     */
+    int backend_fd;
 };
 typedef struct NVDIMMDevice NVDIMMDevice;
 
@@ -132,4 +144,5 @@ void nvdimm_build_acpi(GArray *table_offsets, GArray 
*table_data,
                        uint32_t ram_slots);
 void nvdimm_plug(AcpiNVDIMMState *state);
 void nvdimm_acpi_plug_cb(HotplugHandler *hotplug_dev, DeviceState *dev);
+void nvdimm_flush(NVDIMMDevice *nvdimm);
 #endif
-- 
2.10.1