block/cow.c: fix warnings with _FORTIFY_SOURCE

CC    block/cow.o
cc1: warnings being treated as errors
block/cow.c: In function 'cow_create':
block/cow.c:251: error: ignoring return value of 'write', declared with attribute warn_unused_result
block/cow.c:253: error: ignoring return value of 'ftruncate', declared with attribute warn_unused_result
make: *** [block/cow.o] Error 1
Signed-off-by: NKirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: NJuan Quintela <quintela@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

block/cow.c

@@ -209,6 +209,7 @@ static int cow_create(const char *filename, QEMUOptionParameter *options)
     struct stat st;
     int64_t image_sectors = 0;
     const char *image_filename = NULL;
+    int ret;
 
     /* Read out options */
     while (options && options->name) {
@@ -248,11 +249,23 @@ static int cow_create(const char *filename, QEMUOptionParameter *options)
     }
     cow_header.sectorsize = cpu_to_be32(512);
     cow_header.size = cpu_to_be64(image_sectors * 512);
-    write(cow_fd, &cow_header, sizeof(cow_header));
+    ret = qemu_write_full(cow_fd, &cow_header, sizeof(cow_header));
+    if (ret != sizeof(cow_header)) {
+        ret = -1;
+        goto exit;
+    }
+
     /* resize to include at least all the bitmap */
-    ftruncate(cow_fd, sizeof(cow_header) + ((image_sectors + 7) >> 3));
+    ret = ftruncate(cow_fd, sizeof(cow_header) + ((image_sectors + 7) >> 3));
+    if (ret) {
+        ret = -errno;
+        goto exit;
+    }
+
+    ret = 0;
+exit:
     close(cow_fd);
-    return 0;
+    return ret;
 }
 
 static void cow_flush(BlockDriverState *bs)