Clarify bitfield padding issue (#445)

* Clarify bitfield padding issue

* Add a more elaborate note to fuse_file_info

diff --git a/include/fuse_common.h b/include/fuse_common.h
index 0481aac4a5f8cc733955e455deceae4958d88b8c..efee19485c6387afdec5c244bda6d0f60fc39d85 100644 (file)
--- a/include/fuse_common.h
+++ b/include/fuse_common.h
@@ -83,7 +83,13 @@ struct fuse_file_info {
        unsigned int cache_readdir : 1;
 
        /** Padding.  Reserved for future use*/
-       unsigned int padding : 26;
+       unsigned int padding : 25;
+       /* The following int was once allocated by accident, it is kept for
+          backwards compatibility. `padding2` may be used to implement additional
+          flags in the future just like `padding`. For the sake of compatibility
+          make sure that the bitfields fit into blocks of 32 bits exactly so that
+          no hidden padding exists in between. */
+       unsigned int padding2 : 32;
 
        /** File handle id.  May be filled in by filesystem in create,
         * open, and opendir().  Available in most other file operations on the
@@ -246,7 +252,7 @@ struct fuse_loop_config {
 #define FUSE_CAP_READDIRPLUS           (1 << 13)
 
 /**
- * Indicates that the filesystem supports adaptive readdirplus. 
+ * Indicates that the filesystem supports adaptive readdirplus.
  *
  * If FUSE_CAP_READDIRPLUS is not set, this flag has no effect.
  *