blktrace: use rbuf->stats.full as a drop indicator in relayfs

Replace internal subbuf_start in blktrace with the default policy in
relayfs.

Remove dropped field from struct blktrace.  Correspondingly, call the
common helper in relay.  By incrementing full_count to keep track of how
many times we encountered a full buffer issue, user space will know how
many events were lost.

Link: https://lkml.kernel.org/r/20250612061201.34272-5-kerneljasonxing@gmail.com
Signed-off-by: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Yushan Zhou <katrinzhou@tencent.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
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/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index d3083c88474e6a4c8c83cd43de963a76738f425e..5401b90061355aed30d78892b163c652de24fef5 100644 (file)
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -415,9 +415,10 @@ static ssize_t blk_dropped_read(struct file *filp, char __user *buffer,
                                size_t count, loff_t *ppos)
 {
        struct blk_trace *bt = filp->private_data;
+       size_t dropped = relay_stats(bt->rchan, RELAY_STATS_BUF_FULL);
        char buf[16];
 
-       snprintf(buf, sizeof(buf), "%u\n", atomic_read(&bt->dropped));
+       snprintf(buf, sizeof(buf), "%zu\n", dropped);
 
        return simple_read_from_buffer(buffer, count, ppos, buf, strlen(buf));
 }
@@ -456,23 +457,6 @@ static const struct file_operations blk_msg_fops = {
        .llseek =       noop_llseek,
 };
 
-/*
- * Keep track of how many times we encountered a full subbuffer, to aid
- * 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)
-{
-       struct blk_trace *bt;
-
-       if (!relay_buf_full(buf))
-               return 1;
-
-       bt = buf->chan->private_data;
-       atomic_inc(&bt->dropped);
-       return 0;
-}
-
 static int blk_remove_buf_file_callback(struct dentry *dentry)
 {
        debugfs_remove(dentry);
@@ -491,7 +475,6 @@ static struct dentry *blk_create_buf_file_callback(const char *filename,
 }
 
 static const struct rchan_callbacks blk_relay_callbacks = {
-       .subbuf_start           = blk_subbuf_start_callback,
        .create_buf_file        = blk_create_buf_file_callback,
        .remove_buf_file        = blk_remove_buf_file_callback,
 };
@@ -580,7 +563,6 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
        }
 
        bt->dev = dev;
-       atomic_set(&bt->dropped, 0);
        INIT_LIST_HEAD(&bt->running_list);
 
        ret = -EIO;