From c245d0d3253680f0f8caf751ae99d10bd74034bf Mon Sep 17 00:00:00 2001
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 30 May 2018 02:11:43 +0200
Subject: [PATCH] Implement ring buffer clear

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
 lib/ringbuffer/frontend_internal.h    | 26 ++++++++++++++++++++++++++
 lib/ringbuffer/ring_buffer_frontend.c | 10 ++++++++++
 lib/ringbuffer/ring_buffer_vfs.c      |  6 ++++++
 lib/ringbuffer/vfs.h                  |  5 +++++
 4 files changed, 47 insertions(+)

diff --git a/lib/ringbuffer/frontend_internal.h b/lib/ringbuffer/frontend_internal.h
index d02a73d3..a1bfe558 100644
--- a/lib/ringbuffer/frontend_internal.h
+++ b/lib/ringbuffer/frontend_internal.h
@@ -154,6 +154,8 @@ extern
 void lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf);
 extern
 void lib_ring_buffer_switch_remote_empty(struct lib_ring_buffer *buf);
+extern
+void lib_ring_buffer_clear(struct lib_ring_buffer *buf);
 
 /* Buffer write helpers */
 
@@ -185,6 +187,30 @@ void lib_ring_buffer_reserve_push_reader(struct lib_ring_buffer *buf,
 					      consumed_new) != consumed_old));
 }
 
+/*
+ * Move consumed position to the beginning of subbuffer in which the
+ * write offset is.
+ */
+static inline
+void lib_ring_buffer_clear_reader(struct lib_ring_buffer *buf,
+				  struct channel *chan)
+{
+	const struct lib_ring_buffer_config *config = &chan->backend.config;
+	unsigned long offset, consumed_old, consumed_new;
+
+	do {
+		offset = v_read(config, &buf->offset);
+		consumed_old = atomic_long_read(&buf->consumed);
+		if (unlikely(subbuf_trunc(offset, chan)
+			      - subbuf_trunc(consumed_old, chan)
+			     > 0))
+			consumed_new = subbuf_trunc(offset, chan);
+		else
+			return;
+	} while (unlikely(atomic_long_cmpxchg(&buf->consumed, consumed_old,
+					      consumed_new) != consumed_old));
+}
+
 static inline
 int lib_ring_buffer_pending_data(const struct lib_ring_buffer_config *config,
 				 struct lib_ring_buffer *buf,
diff --git a/lib/ringbuffer/ring_buffer_frontend.c b/lib/ringbuffer/ring_buffer_frontend.c
index 0d2d6936..3cab3652 100644
--- a/lib/ringbuffer/ring_buffer_frontend.c
+++ b/lib/ringbuffer/ring_buffer_frontend.c
@@ -1957,6 +1957,16 @@ void lib_ring_buffer_switch_remote_empty(struct lib_ring_buffer *buf)
 }
 EXPORT_SYMBOL_GPL(lib_ring_buffer_switch_remote_empty);
 
+void lib_ring_buffer_clear(struct lib_ring_buffer *buf)
+{
+	struct lib_ring_buffer_backend *bufb = &buf->backend;
+	struct channel *chan = bufb->chan;
+
+	lib_ring_buffer_switch_remote(buf);
+	lib_ring_buffer_clear_reader(buf, chan);
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_clear);
+
 /*
  * Returns :
  * 0 if ok
diff --git a/lib/ringbuffer/ring_buffer_vfs.c b/lib/ringbuffer/ring_buffer_vfs.c
index f6c0e3df..b423432d 100644
--- a/lib/ringbuffer/ring_buffer_vfs.c
+++ b/lib/ringbuffer/ring_buffer_vfs.c
@@ -263,6 +263,9 @@ long lib_ring_buffer_ioctl(struct file *filp, unsigned int cmd,
 	case RING_BUFFER_FLUSH_EMPTY:
 		lib_ring_buffer_switch_remote_empty(buf);
 		return 0;
+	case RING_BUFFER_CLEAR:
+		lib_ring_buffer_clear(buf);
+		return 0;
 	default:
 		return -ENOIOCTLCMD;
 	}
@@ -414,6 +417,9 @@ long lib_ring_buffer_compat_ioctl(struct file *filp, unsigned int cmd,
 	case RING_BUFFER_COMPAT_FLUSH_EMPTY:
 		lib_ring_buffer_switch_remote_empty(buf);
 		return 0;
+	case RING_BUFFER_COMPAT_CLEAR:
+		lib_ring_buffer_clear(buf);
+		return 0;
 	default:
 		return -ENOIOCTLCMD;
 	}
diff --git a/lib/ringbuffer/vfs.h b/lib/ringbuffer/vfs.h
index b30b0f58..2061156d 100644
--- a/lib/ringbuffer/vfs.h
+++ b/lib/ringbuffer/vfs.h
@@ -112,6 +112,8 @@ ssize_t vfs_lib_ring_buffer_splice_read(struct file *in, loff_t *ppos,
  * so it can be read again.
  */
 #define RING_BUFFER_METADATA_CACHE_DUMP		_IO(0xF6, 0x10)
+/* Clear ring buffer content. */
+#define RING_BUFFER_CLEAR			_IO(0xF6, 0x11)
 
 #ifdef CONFIG_COMPAT
 /* Get a snapshot of the current ring buffer producer and consumer positions */
@@ -156,6 +158,9 @@ ssize_t vfs_lib_ring_buffer_splice_read(struct file *in, loff_t *ppos,
 /* Flush the current sub-buffer, even if empty. */
 #define RING_BUFFER_COMPAT_FLUSH_EMPTY			\
 	RING_BUFFER_FLUSH_EMPTY
+/* Clear ring buffer content. */
+#define RING_BUFFER_COMPAT_CLEAR			\
+	RING_BUFFER_CLEAR
 #endif /* CONFIG_COMPAT */
 
 #endif /* _LIB_RING_BUFFER_VFS_H */
-- 
2.34.1