diff -Nru qemu.org/block/sheepdog.c qemu/block/sheepdog.c
--- qemu.org/block/sheepdog.c	2011-05-16 20:31:15.000000000 +0900
+++ qemu/block/sheepdog.c	2011-05-16 20:39:46.000000000 +0900
@@ -1292,12 +1292,65 @@
     return 0;
 }
 
+static int sd_prealloc(uint32_t vid, int64_t vdi_size)
+{
+    int fd, ret;
+    SheepdogInode *inode;
+    char *buf;
+    unsigned long idx, max_idx;
+
+    fd = connect_to_sdog(NULL, NULL);
+    if (fd < 0) {
+        return -EIO;
+    }
+
+    inode = qemu_malloc(sizeof(*inode));
+    buf = qemu_malloc(SD_DATA_OBJ_SIZE);
+
+    ret = read_object(fd, (char *)inode, vid_to_vdi_oid(vid),
+                      0, sizeof(*inode), 0);
+
+    max_idx = (vdi_size + SD_DATA_OBJ_SIZE - 1) / SD_DATA_OBJ_SIZE;
+
+    for (idx = 0; idx < max_idx; idx++) {
+        uint64_t oid;
+        oid = vid_to_data_oid(vid, idx);
+
+        if (inode->data_vdi_id[idx]) {
+            ret = read_object(fd, buf, vid_to_vdi_oid(inode->data_vdi_id[idx]),
+                              1, SD_DATA_OBJ_SIZE, 0);
+            if (ret)
+                goto out;
+        } else {
+            memset(buf, 0, SD_DATA_OBJ_SIZE);
+        }
+
+        ret = write_object(fd, buf, oid, 1, SD_DATA_OBJ_SIZE, 0, 1);
+        if (ret)
+            goto out;
+
+        inode->data_vdi_id[idx] = vid;
+        ret = write_object(fd, (char *)inode, vid_to_vdi_oid(vid),
+                           1, sizeof(*inode), 0, 0);
+        if (ret)
+            goto out;
+    }
+out:
+    free(inode);
+    free(buf);
+    closesocket(fd);
+
+    return ret;
+}
+
+
 static int sd_create(const char *filename, QEMUOptionParameter *options)
 {
     int ret;
     uint32_t vid = 0, base_vid = 0;
     int64_t vdi_size = 0;
     char *backing_file = NULL;
+	int prealloc = 0;
     BDRVSheepdogState s;
     char vdi[SD_MAX_VDI_LEN], tag[SD_MAX_VDI_TAG_LEN];
     uint32_t snapid;
@@ -1317,7 +1370,18 @@
             vdi_size = options->value.n;
         } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) {
             backing_file = options->value.s;
-        }
+        } else if (!strcmp(options->name, BLOCK_OPT_PREALLOC)) {
+            if (!options->value.s || !strcmp(options->value.s, "off")) {
+                prealloc = 0;
+            } else if (!strcmp(options->value.s, "data")) {
+                prealloc = 1;
+            } else {
+                error_report("Invalid preallocation mode: '%s'\n",
+                    options->value.s);
+                return -EINVAL;
+            }
+
+		}
         options++;
     }
 
@@ -1353,8 +1417,12 @@
         base_vid = s->inode.vdi_id;
         bdrv_delete(bs);
     }
+    ret = do_sd_create((char *)filename, vdi_size, base_vid, &vid, 0, NULL, NULL);
+    if (!prealloc || ret)
+        return ret;
+
+    return sd_prealloc(vid, vdi_size);
 
-    return do_sd_create((char *)vdi, vdi_size, base_vid, &vid, 0, s.addr, s.port);
 }
 
 static void sd_close(BlockDriverState *bs)
@@ -1990,6 +2058,11 @@
         .type = OPT_STRING,
         .help = "File name of a base image"
     },
+	{
+        .name = BLOCK_OPT_PREALLOC,
+        .type = OPT_STRING,
+        .help = "Preallocation mode (allowed values: off, data)"
+    },
     { NULL }
 };