[PATCH v2 2/4] relayfs: introduce dump of relayfs statistics function

[Jason Xing <kerneljasonxing@gmail.com>]

From: Jason Xing <kernelxing@tencent.com>

In this version, only support dumping the counter for buffer full and
implement the framework of how it works.

Users can pass certain flag to fetch what field/statistics they expect
to know. Each time it only returns one result. So do not pass multiple
flags.

Reviewed-by: Yushan Zhou <katrinzhou@tencent.com>
Signed-off-by: Jason Xing <kernelxing@tencent.com>
---
v2
1. refactor relay_dump() and make it only return a pure size_t result
of the value that users specifies.
2. revise the commit log.
---
 include/linux/relay.h |  7 +++++++
 kernel/relay.c        | 31 +++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/include/linux/relay.h b/include/linux/relay.h
index ce7a1b396872..3fb285716e34 100644
--- a/include/linux/relay.h
+++ b/include/linux/relay.h
@@ -31,6 +31,12 @@
 /*
  * Relay buffer statistics dump
  */
+enum {
+	RELAY_DUMP_BUF_FULL = (1 << 0),
+
+	RELAY_DUMP_LAST = RELAY_DUMP_BUF_FULL,
+};
+
 struct rchan_buf_stats
 {
 	unsigned int full_count;	/* counter for buffer full */
@@ -167,6 +173,7 @@ struct rchan *relay_open(const char *base_filename,
 			 void *private_data);
 extern void relay_close(struct rchan *chan);
 extern void relay_flush(struct rchan *chan);
+extern size_t relay_dump(struct rchan *chan, int flags);
 extern void relay_subbufs_consumed(struct rchan *chan,
 				   unsigned int cpu,
 				   size_t consumed);
diff --git a/kernel/relay.c b/kernel/relay.c
index eb3f630f3896..f47fc750e559 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -701,6 +701,37 @@ void relay_flush(struct rchan *chan)
 }
 EXPORT_SYMBOL_GPL(relay_flush);
 
+/**
+ *	relay_dump - dump channel buffer statistics
+ *	@chan: the channel
+ *	@flags: select particular information to dump
+ *
+ *	Returns the count of certain field that caller specifies.
+ */
+size_t relay_dump(struct rchan *chan, int flags)
+{
+	unsigned int i, count = 0;
+	struct rchan_buf *rbuf;
+
+	if (!chan || flags > RELAY_DUMP_LAST)
+		return 0;
+
+	if (chan->is_global) {
+		rbuf = *per_cpu_ptr(chan->buf, 0);
+		if (flags & RELAY_DUMP_BUF_FULL)
+			count = rbuf->stats.full_count;
+	} else {
+		for_each_online_cpu(i) {
+			if ((rbuf = *per_cpu_ptr(chan->buf, i)))
+				if (flags & RELAY_DUMP_BUF_FULL)
+					count += rbuf->stats.full_count;
+		}
+	}
+
+	return count;
+}
+EXPORT_SYMBOL_GPL(relay_dump);
+
 /**
  *	relay_file_open - open file op for relay files
  *	@inode: the inode
-- 
2.43.5