storage: Flush host cache after write

Although we are flushing cache after some critical writes (e.g.
volume creation), after some others we do not (e.g. volume cloning).
This patch fix this issue. That is for volume cloning, writing
header of logical volume, and storage wipe.

src/storage/storage_backend.c

@@ -208,6 +208,14 @@ virStorageBackendCopyToFD(virStorageVolDefPtr vol,
         } while ((amtleft -= interval) > 0);
     }
 
+    if (fdatasync(fd) < 0) {
+        ret = -errno;
+        virReportSystemError(errno, _("cannot sync data to file '%s'"),
+                             vol->target.path);
+        goto cleanup;
+    }
+
+
     if (VIR_CLOSE(inputfd) < 0) {
         ret = -errno;
         virReportSystemError(errno,

src/storage/storage_backend_logical.c

@@ -424,6 +424,13 @@ virStorageBackendLogicalBuildPool(virConnectPtr conn ATTRIBUTE_UNUSED,
             VIR_FORCE_CLOSE(fd);
             goto cleanup;
         }
+        if (fsync(fd) < 0) {
+            virReportSystemError(errno,
+                                 _("cannot flush header of device'%s'"),
+                                 pool->def->source.devices[i].path);
+            VIR_FORCE_CLOSE(fd);
+            goto cleanup;
+        }
         if (VIR_CLOSE(fd) < 0) {
             virReportSystemError(errno,
                                  _("cannot close device '%s'"),

src/storage/storage_driver.c

@@ -1777,6 +1777,14 @@ storageWipeExtent(virStorageVolDefPtr vol,
         remaining -= written;
     }
 
+    if (fdatasync(fd) < 0) {
+        ret = -errno;
+        virReportSystemError(errno,
+                             _("cannot sync data to volume with path '%s'"),
+                             vol->target.path);
+        goto out;
+    }
+
     VIR_DEBUG("Wrote %zu bytes to volume with path '%s'",
               *bytes_wiped, vol->target.path);