binder: Split flat_binder_object

flat_binder_object is used for both handling
binder objects and file descriptors, even though
the two are mostly independent. Since we'll
have more fixup objects in binder in the future,
instead of extending flat_binder_object again,
split out file descriptors to their own object
while retaining backwards compatibility to
existing user-space clients. All binder objects
just share a header.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Martijn Coenen <maco@google.com>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Amit Pundir <amit.pundir@linaro.org>
Cc: Serban Constantinescu <serban.constantinescu@arm.com>
Cc: Dmitry Shmidt <dimitrysh@google.com>
Cc: Rom Lemarchand <romlem@google.com>
Cc: Android Kernel Team <kernel-team@android.com>
Signed-off-by: Martijn Coenen <maco@google.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/uapi/linux/android/binder.h

@@ -48,6 +48,14 @@ typedef __u64 binder_size_t;
 typedef __u64 binder_uintptr_t;
 #endif
 
+/**
+ * struct binder_object_header - header shared by all binder metadata objects.
+ * @type:	type of the object
+ */
+struct binder_object_header {
+	__u32        type;
+};
+
 /*
  * This is the flattened representation of a Binder object for transfer
  * between processes.  The 'offsets' supplied as part of a binder transaction
@@ -56,9 +64,8 @@ typedef __u64 binder_uintptr_t;
  * between processes.
  */
 struct flat_binder_object {
-	/* 8 bytes for large_flat_header. */
-	__u32		type;
-	__u32		flags;
+	struct binder_object_header	hdr;
+	__u32				flags;
 
 	/* 8 bytes of data. */
 	union {
@@ -70,6 +77,24 @@ struct flat_binder_object {
 	binder_uintptr_t	cookie;
 };
 
+/**
+ * struct binder_fd_object - describes a filedescriptor to be fixed up.
+ * @hdr:	common header structure
+ * @pad_flags:	padding to remain compatible with old userspace code
+ * @pad_binder:	padding to remain compatible with old userspace code
+ * @fd:		file descriptor
+ * @cookie:	opaque data, used by user-space
+ */
+struct binder_fd_object {
+	struct binder_object_header	hdr;
+	__u32				pad_flags;
+	union {
+		binder_uintptr_t	pad_binder;
+		__u32			fd;
+	};
+
+	binder_uintptr_t		cookie;
+};
 /*
  * On 64-bit platforms where user code may run in 32-bits the driver must
  * translate the buffer (and local binder) addresses appropriately.