V4L/DVB (7658): dvb-core: Fix DMX_SET_BUFFER_SIZE in case the buffer shrinks

This patch fixes the bug in DMX_SET_BUFFER_SIZE for the demux.
Basically it resets read and write pointers to 0 in case they are
beyond the new size of the buffer.

Signed-off-by: Andrea Odetti <mariofutire@gmail.com>
Signed-off-by: Oliver Endriss <o.endriss@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/dvb/dvb-core/dmxdev.c

@@ -281,7 +281,9 @@ static int dvb_dmxdev_set_buffer_size(struct dmxdev_filter *dmxdevfilter,
 	mem = buf->data;
 	buf->data = NULL;
 	buf->size = size;
-	dvb_ringbuffer_flush(buf);
+
+	/* reset and not flush in case the buffer shrinks */
+	dvb_ringbuffer_reset(buf);
 	spin_unlock_irq(&dmxdevfilter->dev->lock);
 	vfree(mem);
 

drivers/media/dvb/dvb-core/dvb_ringbuffer.c

@@ -90,7 +90,11 @@ void dvb_ringbuffer_flush(struct dvb_ringbuffer *rbuf)
 	rbuf->error = 0;
 }
 
-
+void dvb_ringbuffer_reset(struct dvb_ringbuffer *rbuf)
+{
+	rbuf->pread = rbuf->pwrite = 0;
+	rbuf->error = 0;
+}
 
 void dvb_ringbuffer_flush_spinlock_wakeup(struct dvb_ringbuffer *rbuf)
 {

drivers/media/dvb/dvb-core/dvb_ringbuffer.h

@@ -69,6 +69,7 @@ struct dvb_ringbuffer {
 **     to lock read or write operations.
 **     Two or more readers must be locked against each other.
 **     Flushing the buffer counts as a read operation.
+**     Resetting the buffer counts as a read and write operation.
 **     Two or more writers must be locked against each other.
 */
 
@@ -85,6 +86,13 @@ extern ssize_t dvb_ringbuffer_free(struct dvb_ringbuffer *rbuf);
 extern ssize_t dvb_ringbuffer_avail(struct dvb_ringbuffer *rbuf);
 
 
+/*
+** Reset the read and write pointers to zero and flush the buffer
+** This counts as a read and write operation
+*/
+extern void dvb_ringbuffer_reset(struct dvb_ringbuffer *rbuf);
+
+
 /* read routines & macros */
 /* ---------------------- */
 /* flush buffer */