Rewrite V4L2 controls to keep a list of them (fix #5269)

The V4L2 plug-in is a bit peculiar with dynamically generated object
variables. We need to keep track of which controls/variables we have,
so that we can remove the variables callbacks later. The only other
way to solve this bug, that I could think of, consisted of extending
the VLC variables subsystem (which would be worse in code freeze).

This rewrite also fixes a few other bugs:
 * Support menu with non-zero based minumum choice
 * Support menu with discontinuous choices range
 * Redumdant use the extended controls API as fallback
   (This only makes sense to set more than one control at a time,
    or to set 64-bits and string controls. VLC does none of that.)
 * Unused "controls-update" and "allcontrols" variables.
 * Skipping disabled, read-only and volatile controls.

Support for the legacy control enumeration API (pre-2.6.18 kernel) is
removed; and the code is now independent of the VLC object type (it
could easily be reused for say, a V4L2 video output).

modules/access/v4l2/access.c

@@ -73,6 +73,7 @@ void AccessClose( vlc_object_t *obj )
     access_t *access = (access_t *)obj;
     demux_sys_t *sys = (demux_sys_t *)access->p_sys;
 
+    ControlsDeinit( obj, sys->controls );
     v4l2_close( sys->i_fd );
     free( sys );
 }

modules/access/v4l2/demux.c

@@ -116,6 +116,7 @@ void DemuxClose( vlc_object_t *obj )
         free( sys->p_buffers );
     }
 
+    ControlsDeinit( obj, sys->controls );
     v4l2_close( fd );
     free( sys );
 }

modules/access/v4l2/v4l2.h

@@ -41,8 +41,6 @@
 
 #define CFG_PREFIX "v4l2-"
 
-int ControlList(vlc_object_t *, int fd, bool b_demux);
-
 /* TODO: remove this, use callbacks */
 typedef enum {
     IO_METHOD_READ=1,
@@ -50,7 +48,9 @@ typedef enum {
     IO_METHOD_USERPTR,
 } io_method;
 
-/* TODO: move this to .c */
+typedef struct vlc_v4l2_ctrl vlc_v4l2_ctrl_t;
+
+/* TODO: move this to access.c and demux.c (separately) */
 struct demux_sys_t
 {
     int  i_fd;
@@ -67,6 +67,8 @@ struct demux_sys_t
 
     es_out_id_t *p_es;
 
+    vlc_v4l2_ctrl_t *controls;
+
 #ifdef HAVE_LIBV4L2
     bool b_libv4l2;
 #endif
@@ -93,3 +95,7 @@ void GetMaxDimensions(vlc_object_t *, int fd, uint32_t fmt, float fps_min,
 /* access.c */
 int AccessOpen(vlc_object_t *);
 void AccessClose(vlc_object_t *);
+
+/* controls.c */
+vlc_v4l2_ctrl_t *ControlsInit(vlc_object_t *, int fd);
+void ControlsDeinit(vlc_object_t *, vlc_v4l2_ctrl_t *);

modules/access/v4l2/video.c

@@ -1036,7 +1036,7 @@ static int InitVideo( vlc_object_t *p_obj, int i_fd, demux_sys_t *p_sys,
 
     /* TODO: Move the resolution stuff up here */
     /* if MPEG encoder card, no need to do anything else after this */
-    ControlList( p_obj, i_fd, b_demux );
+    p_sys->controls = ControlsInit( p_obj, i_fd );
 
     /* Reset Cropping */
     memset( &cropcap, 0, sizeof(cropcap) );