curl: Support auto-read-only option

If read-only=off, but auto-read-only=on is given, just degrade to
read-only.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

block/curl.c

@@ -684,10 +684,10 @@ static int curl_open(BlockDriverState *bs, QDict *options, int flags,
     const char *protocol_delimiter;
     int ret;
 
-
-    if (flags & BDRV_O_RDWR) {
-        error_setg(errp, "curl block device does not support writes");
-        return -EROFS;
+    ret = bdrv_apply_auto_read_only(bs, "curl driver does not support writes",
+                                    errp);
+    if (ret < 0) {
+        return ret;
     }
 
     if (!libcurl_initialized) {