[PATCH] relayfs: abolish prev_padding

[Jason Xing <kerneljasonxing@gmail.com>]

From: Jason Xing <kernelxing@tencent.com>

prev_padding represents the unused space of certain subbuffer. If the
content of a call of relay_write() exceeds the limit of the remainder of
this subbuffer, it will skip storing in the rest space and record the
start point as buf->prev_padding in relay_switch_subbuf(). Since the buf
is a per-cpu big buffer, the point of prev_padding as a global value for
the whole buffer instead of a single subbuffer (whose padding info is
stored in buf->padding[]) seems meaningless from the real use cases, so
we don't bother to record it any more.

Reviewed-by: Yushan Zhou <katrinzhou@tencent.com>
Signed-off-by: Jason Xing <kernelxing@tencent.com>
---
 drivers/gpu/drm/i915/gt/uc/intel_guc_log.c |  3 +--
 drivers/net/wwan/iosm/iosm_ipc_trace.c     |  3 +--
 drivers/net/wwan/t7xx/t7xx_port_trace.c    |  2 +-
 include/linux/relay.h                      |  5 +----
 kernel/relay.c                             | 14 ++++++++------
 kernel/trace/blktrace.c                    |  2 +-
 6 files changed, 13 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_log.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_log.c
index e8a04e476c57..09a64f224c49 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_log.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_log.c
@@ -220,8 +220,7 @@ static int guc_action_control_log(struct intel_guc *guc, bool enable,
  */
 static int subbuf_start_callback(struct rchan_buf *buf,
 				 void *subbuf,
-				 void *prev_subbuf,
-				 size_t prev_padding)
+				 void *prev_subbuf)
 {
 	/*
 	 * Use no-overwrite mode by default, where relay will stop accepting
diff --git a/drivers/net/wwan/iosm/iosm_ipc_trace.c b/drivers/net/wwan/iosm/iosm_ipc_trace.c
index eeecfa3d10c5..9656254c1c6c 100644
--- a/drivers/net/wwan/iosm/iosm_ipc_trace.c
+++ b/drivers/net/wwan/iosm/iosm_ipc_trace.c
@@ -51,8 +51,7 @@ static int ipc_trace_remove_buf_file_handler(struct dentry *dentry)
 }
 
 static int ipc_trace_subbuf_start_handler(struct rchan_buf *buf, void *subbuf,
-					  void *prev_subbuf,
-					  size_t prev_padding)
+					  void *prev_subbuf)
 {
 	if (relay_buf_full(buf)) {
 		pr_err_ratelimited("Relay_buf full dropping traces");
diff --git a/drivers/net/wwan/t7xx/t7xx_port_trace.c b/drivers/net/wwan/t7xx/t7xx_port_trace.c
index 4ed8b4e29bf1..f16d3b01302c 100644
--- a/drivers/net/wwan/t7xx/t7xx_port_trace.c
+++ b/drivers/net/wwan/t7xx/t7xx_port_trace.c
@@ -33,7 +33,7 @@ static int t7xx_trace_remove_buf_file_handler(struct dentry *dentry)
 }
 
 static int t7xx_trace_subbuf_start_handler(struct rchan_buf *buf, void *subbuf,
-					   void *prev_subbuf, size_t prev_padding)
+					   void *prev_subbuf)
 {
 	if (relay_buf_full(buf)) {
 		pr_err_ratelimited("Relay_buf full dropping traces");
diff --git a/include/linux/relay.h b/include/linux/relay.h
index 72b876dd5cb8..f80b0eb1e905 100644
--- a/include/linux/relay.h
+++ b/include/linux/relay.h
@@ -47,7 +47,6 @@ struct rchan_buf
 	unsigned int page_count;	/* number of current buffer pages */
 	unsigned int finalized;		/* buffer has been finalized */
 	size_t *padding;		/* padding counts per sub-buffer */
-	size_t prev_padding;		/* temporary variable */
 	size_t bytes_consumed;		/* bytes consumed in cur read subbuf */
 	size_t early_bytes;		/* bytes consumed before VFS inited */
 	unsigned int cpu;		/* this buf's cpu */
@@ -84,7 +83,6 @@ struct rchan_callbacks
 	 * @buf: the channel buffer containing the new sub-buffer
 	 * @subbuf: the start of the new sub-buffer
 	 * @prev_subbuf: the start of the previous sub-buffer
-	 * @prev_padding: unused space at the end of previous sub-buffer
 	 *
 	 * The client should return 1 to continue logging, 0 to stop
 	 * logging.
@@ -100,8 +98,7 @@ struct rchan_callbacks
 	 */
 	int (*subbuf_start) (struct rchan_buf *buf,
 			     void *subbuf,
-			     void *prev_subbuf,
-			     size_t prev_padding);
+			     void *prev_subbuf);
 
 	/*
 	 * create_buf_file - create file to represent a relay channel buffer
diff --git a/kernel/relay.c b/kernel/relay.c
index 5ac7e711e4b6..5aeb9226e238 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -250,13 +250,13 @@ EXPORT_SYMBOL_GPL(relay_buf_full);
  */
 
 static int relay_subbuf_start(struct rchan_buf *buf, void *subbuf,
-			      void *prev_subbuf, size_t prev_padding)
+			      void *prev_subbuf)
 {
 	if (!buf->chan->cb->subbuf_start)
 		return !relay_buf_full(buf);
 
 	return buf->chan->cb->subbuf_start(buf, subbuf,
-					   prev_subbuf, prev_padding);
+					   prev_subbuf);
 }
 
 /**
@@ -302,7 +302,7 @@ static void __relay_reset(struct rchan_buf *buf, unsigned int init)
 	for (i = 0; i < buf->chan->n_subbufs; i++)
 		buf->padding[i] = 0;
 
-	relay_subbuf_start(buf, buf->data, NULL, 0);
+	relay_subbuf_start(buf, buf->data, NULL);
 }
 
 /**
@@ -664,9 +664,11 @@ size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
 		goto toobig;
 
 	if (buf->offset != buf->chan->subbuf_size + 1) {
-		buf->prev_padding = buf->chan->subbuf_size - buf->offset;
+		size_t prev_padding;
+
+		prev_padding = buf->chan->subbuf_size - buf->offset;
 		old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
-		buf->padding[old_subbuf] = buf->prev_padding;
+		buf->padding[old_subbuf] = prev_padding;
 		buf->subbufs_produced++;
 		if (buf->dentry)
 			d_inode(buf->dentry)->i_size +=
@@ -691,7 +693,7 @@ size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
 	new_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
 	new = buf->start + new_subbuf * buf->chan->subbuf_size;
 	buf->offset = 0;
-	if (!relay_subbuf_start(buf, new, old, buf->prev_padding)) {
+	if (!relay_subbuf_start(buf, new, old)) {
 		buf->offset = buf->chan->subbuf_size + 1;
 		return 0;
 	}
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 3679a6d18934..d1a89714e805 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -461,7 +461,7 @@ static const struct file_operations blk_msg_fops = {
  * the user space app in telling how many lost events there were.
  */
 static int blk_subbuf_start_callback(struct rchan_buf *buf, void *subbuf,
-				     void *prev_subbuf, size_t prev_padding)
+				     void *prev_subbuf)
 {
 	struct blk_trace *bt;
 
-- 
2.43.5