change tut01 to use global buffer

Index: tut01-skeleton-drv.c
===================================================================
@@ -25,7 +25,7 @@
  *  - open:  start device usage
  *  - close: ends device usage
  *  - write: store transfered data in an internal buffer
- *  - read:  return previously stored data and erase buffer
+ *  - read:  return previously stored data
  *
  */
 

@@ -39,17 +39,18 @@
 #define DEVICE_NAME		"tut01-skeleton-drv01"
 #define SOME_SUB_CLASS		4711
 
+
 /**
- * The context of a device instance
+ * The size of the global buffer 
  *
- * A context is created each time a device is opened and passed to
- * other device handlers when they are called.
+ */
+int global_buffer_size = 0;
+
+/**
+ * A global buffer 
  *
  */
-typedef struct buffer_s {
-	int size;
-	char data[SIZE_MAX];
-} buffer_t;
+char global_buffer[SIZE_MAX]; 
 
 /**
  * Open the device

@@ -60,9 +61,6 @@
 static int simple_rtdm_open_nrt(struct rtdm_dev_context *context,
 				rtdm_user_info_t * user_info, int oflags)
 {
-	buffer_t * buffer = (buffer_t *) context->dev_private;
-	buffer->size = 0; /* clear the buffer */
-
 	return 0;
 }
 

@@ -88,11 +86,9 @@
 				    rtdm_user_info_t * user_info, void *buf,
 				    size_t nbyte)
 {
-	buffer_t * buffer = (buffer_t *) context->dev_private;
-	int size = (buffer->size > nbyte) ? nbyte : buffer->size;
+	int size = (global_buffer_size > nbyte) ? nbyte : global_buffer_size; 
 
-	buffer->size = 0;
-	if (rtdm_safe_copy_to_user(user_info, buf, buffer->data, size))
+	if (rtdm_safe_copy_to_user(user_info, buf, global_buffer, size))
 		rtdm_printk("ERROR : can't copy data from driver\n");
 
 	return size;

@@ -108,13 +104,12 @@
 				     rtdm_user_info_t * user_info,
 				     const void *buf, size_t nbyte)
 {
-	buffer_t * buffer = (buffer_t *) context->dev_private;
+	global_buffer_size = (nbyte > SIZE_MAX) ? SIZE_MAX : nbyte;
 
-	buffer->size = (nbyte > SIZE_MAX) ? SIZE_MAX : nbyte;
-	if (rtdm_safe_copy_from_user(user_info, buffer->data, buf, buffer->size))
+	if (rtdm_safe_copy_from_user(user_info, global_buffer, buf, global_buffer_size))
 		rtdm_printk("ERROR : can't copy data to driver\n");
 
-	return nbyte;
+	return global_buffer_size;
 }
 
 /**

@@ -125,7 +120,7 @@
 	.struct_version = RTDM_DEVICE_STRUCT_VER,
 
 	.device_flags = RTDM_NAMED_DEVICE,
-	.context_size = sizeof(buffer_t),
+	.context_size = 0,				/* no context for this device */
 	.device_name = DEVICE_NAME,
 
 	.open_nrt = simple_rtdm_open_nrt,

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