From: Jason Xing <kernelx...@tencent.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 <katrinz...@tencent.com>
Signed-off-by: Jason Xing <kernelx...@tencent.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


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