linux-kernel - [PATCH v3 2/4] relayfs: introduce getting relayfs statistics function

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Message-Id: <20250518025734.61479-3-kerneljasonxing@gmail.com>
Date: Sun, 18 May 2025 10:57:32 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: axboe@...nel.dk,
	rostedt@...dmis.org,
	mhiramat@...nel.org,
	mathieu.desnoyers@...icios.com,
	akpm@...ux-foundation.org
Cc: linux-kernel@...r.kernel.org,
	linux-block@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	Jason Xing <kernelxing@...cent.com>,
	Yushan Zhou <katrinzhou@...cent.com>
Subject: [PATCH v3 2/4] relayfs: introduce getting relayfs statistics function

From: Jason Xing <kernelxing@...cent.com>

In this version, only support getting 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@...cent.com>
Signed-off-by: Jason Xing <kernelxing@...cent.com>
---
v3
1. rename and adjust relay_stats()
2. move rbuf init out of if statement

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        | 30 ++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/include/linux/relay.h b/include/linux/relay.h
index cd77eb285a48..5310967f9d74 100644
--- a/include/linux/relay.h
+++ b/include/linux/relay.h
@@ -31,6 +31,12 @@
 /*
  * Relay buffer statistics
  */
+enum {
+	RELAY_STATS_BUF_FULL = (1 << 0),
+
+	RELAY_STATS_LAST = RELAY_STATS_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);
+size_t relay_stats(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..fd70d0e03216 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -701,6 +701,36 @@ void relay_flush(struct rchan *chan)
 }
 EXPORT_SYMBOL_GPL(relay_flush);
 
+/**
+ *	relay_stats - get channel buffer statistics
+ *	@chan: the channel
+ *	@flags: select particular information to get
+ *
+ *	Returns the count of certain field that caller specifies.
+ */
+size_t relay_stats(struct rchan *chan, int flags)
+{
+	unsigned int i, count = 0;
+	struct rchan_buf *rbuf;
+
+	if (!chan || flags > RELAY_STATS_LAST)
+		return 0;
+
+	if (chan->is_global) {
+		rbuf = *per_cpu_ptr(chan->buf, 0);
+		if (flags & RELAY_STATS_BUF_FULL)
+			count = rbuf->stats.full_count;
+	} else {
+		for_each_online_cpu(i) {
+			rbuf = *per_cpu_ptr(chan->buf, i);
+			if (rbuf && flags & RELAY_STATS_BUF_FULL)
+				count += rbuf->stats.full_count;
+		}
+	}
+
+	return count;
+}
+
 /**
  *	relay_file_open - open file op for relay files
  *	@inode: the inode
-- 
2.43.5