relayfs: introduce getting relayfs statistics function

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.

Link: https://lkml.kernel.org/r/20250612061201.34272-4-kerneljasonxing@gmail.com
Signed-off-by: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Yushan Zhou <katrinzhou@tencent.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/relay.h b/include/linux/relay.h
index cd77eb285a4807a3abec1787cff0e8f476037bd8..5310967f9d74ccf6434792fa6fd114de98c598a1 100644 (file)
--- 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 4b07efddc2cfe073b28957de0d44eedcb29d930f..2fc27c0e771e215b41928f9a41b488108c9896d6 100644 (file)
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -700,6 +700,36 @@ 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