bs->copy_on_read--;
}
+/*
+ * Returns the flags that bs->file should get, based on the given flags for
+ * the parent BDS
+ */
+static int bdrv_inherited_flags(int flags)
+{
+ /* Enable protocol handling, disable format probing for bs->file */
+ flags |= BDRV_O_PROTOCOL;
+
+ /* Our block drivers take care to send flushes and respect unmap policy,
+ * so we can enable both unconditionally on lower layers. */
+ flags |= BDRV_O_CACHE_WB | BDRV_O_UNMAP;
+
+ /* The backing file of a temporary snapshot is read-only */
+ if (flags & BDRV_O_SNAPSHOT) {
+ flags &= ~BDRV_O_RDWR;
+ }
+
+ /* Clear flags that only apply to the top layer */
+ flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING);
+
+ return flags;
+}
+
static int bdrv_open_flags(BlockDriverState *bs, int flags)
{
int open_flags = flags | BDRV_O_CACHE_WB;
assert(file == NULL);
ret = bdrv_open_image(&file, filename, options, "file",
- bdrv_open_flags(bs, flags | BDRV_O_UNMAP) |
- BDRV_O_PROTOCOL, true, &local_err);
+ bdrv_inherited_flags(flags),
+ true, &local_err);
if (ret < 0) {
goto unlink_and_fail;
}