1 files changed, 60 insertions, 4 deletions

diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index 5c626fdc10db..44f2245debda 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -30,9 +30,10 @@ struct pipe_buffer {
  *	struct pipe_inode_info - a linux kernel pipe
  *	@mutex: mutex protecting the whole thing
  *	@wait: reader/writer wait point in case of empty/full pipe
- *	@nrbufs: the number of non-empty pipe buffers in this pipe
- *	@buffers: total number of buffers (should be a power of 2)
- *	@curbuf: the current pipe buffer entry
+ *	@head: The point of buffer production
+ *	@tail: The point of buffer consumption
+ *	@max_usage: The maximum number of slots that may be used in the ring
+ *	@ring_size: total number of buffers (should be a power of 2)
  *	@tmp_page: cached released page
  *	@readers: number of current readers of this pipe
  *	@writers: number of current writers of this pipe
@@ -48,7 +49,10 @@ struct pipe_buffer {
 struct pipe_inode_info {
 	struct mutex mutex;
 	wait_queue_head_t wait;
-	unsigned int nrbufs, curbuf, buffers;
+	unsigned int head;
+	unsigned int tail;
+	unsigned int max_usage;
+	unsigned int ring_size;
 	unsigned int readers;
 	unsigned int writers;
 	unsigned int files;
@@ -105,6 +109,58 @@ struct pipe_buf_operations {
 };
 
 /**
+ * pipe_empty - Return true if the pipe is empty
+ * @head: The pipe ring head pointer
+ * @tail: The pipe ring tail pointer
+ */
+static inline bool pipe_empty(unsigned int head, unsigned int tail)
+{
+	return head == tail;
+}
+
+/**
+ * pipe_occupancy - Return number of slots used in the pipe
+ * @head: The pipe ring head pointer
+ * @tail: The pipe ring tail pointer
+ */
+static inline unsigned int pipe_occupancy(unsigned int head, unsigned int tail)
+{
+	return head - tail;
+}
+
+/**
+ * pipe_full - Return true if the pipe is full
+ * @head: The pipe ring head pointer
+ * @tail: The pipe ring tail pointer
+ * @limit: The maximum amount of slots available.
+ */
+static inline bool pipe_full(unsigned int head, unsigned int tail,
+			     unsigned int limit)
+{
+	return pipe_occupancy(head, tail) >= limit;
+}
+
+/**
+ * pipe_space_for_user - Return number of slots available to userspace
+ * @head: The pipe ring head pointer
+ * @tail: The pipe ring tail pointer
+ * @pipe: The pipe info structure
+ */
+static inline unsigned int pipe_space_for_user(unsigned int head, unsigned int tail,
+					       struct pipe_inode_info *pipe)
+{
+	unsigned int p_occupancy, p_space;
+
+	p_occupancy = pipe_occupancy(head, tail);
+	if (p_occupancy >= pipe->max_usage)
+		return 0;
+	p_space = pipe->ring_size - p_occupancy;
+	if (p_space > pipe->max_usage)
+		p_space = pipe->max_usage;
+	return p_space;
+}
+
+/**
  * pipe_buf_get - get a reference to a pipe_buffer
  * @pipe:	the pipe that the buffer belongs to
  * @buf:	the buffer to get a reference to