linux-kernel - [PATCH v2 03/15] blktrace: split out relaying a blktrace event

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Message-ID: <20250925150231.67342-4-johannes.thumshirn@wdc.com>
Date: Thu, 25 Sep 2025 17:02:19 +0200
From: Johannes Thumshirn <johannes.thumshirn@....com>
To: Jens Axboe <axboe@...nel.dk>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	linux-btrace@...r.kernel.org,
	John Garry <john.g.garry@...cle.com>,
	Hannes Reinecke <hare@...e.de>,
	Damien Le Moal <dlemoal@...nel.org>,
	Christoph Hellwig <hch@....de>,
	Naohiro Aota <naohiro.aota@....com>,
	Shinichiro Kawasaki <shinichiro.kawasaki@....com>,
	Chaitanya Kulkarni <chaitanyak@...dia.com>,
	"Martin K . Petersen" <martin.petersen@...cle.com>,
	Johannes Thumshirn <johannes.thumshirn@....com>
Subject: [PATCH v2 03/15] blktrace: split out relaying a blktrace event

Split out the code relaying a blktrace event to user-space using relayfs.

This enables adding a second version supporting a new version of the
protocol.

Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@....com>
---
 kernel/trace/blktrace.c | 60 ++++++++++++++++++++++-------------------
 1 file changed, 32 insertions(+), 28 deletions(-)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 25a0a1b09747..51745832c713 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -91,6 +91,26 @@ static void record_blktrace_event(struct blk_io_trace *t, pid_t pid, int cpu,
 		memcpy((void *)t + sizeof(*t) + cgid_len, pdu_data, pdu_len);
 }
 
+static void relay_blktrace_event(struct blk_trace *bt, unsigned long sequence,
+				 pid_t pid, int cpu, sector_t sector, int bytes,
+				 u32 what, int error, u64 cgid,
+				 ssize_t cgid_len, void *pdu_data, int pdu_len)
+{
+	struct blk_io_trace *t;
+	size_t trace_len = sizeof(*t) + pdu_len + cgid_len;
+
+	t = relay_reserve(bt->rchan, trace_len);
+	if (!t)
+		return;
+
+	t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION;
+	t->sequence = sequence;
+	t->time = ktime_to_ns(ktime_get());
+
+	record_blktrace_event(t, pid, cpu, sector, bytes, what, bt->dev, error,
+			      cgid, cgid_len, pdu_data, pdu_len);
+}
+
 /*
  * Send out a notify message.
  */
@@ -126,16 +146,9 @@ static void trace_note(struct blk_trace *bt, pid_t pid, int action,
 	if (!bt->rchan)
 		return;
 
-	t = relay_reserve(bt->rchan, trace_len);
-	if (t) {
-		t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION;
-		t->time = ktime_to_ns(ktime_get());
-
-		record_blktrace_event(t, pid, cpu, 0, 0,
-				      action | (cgid ? __BLK_TN_CGROUP : 0),
-				      bt->dev, 0, cgid, cgid_len, (void *)data,
-				      len);
-	}
+	relay_blktrace_event(bt, 0, pid, cpu, 0, 0,
+			     action | (cgid ? __BLK_TN_CGROUP : 0), 0, cgid,
+			     cgid_len, (void *)data, len);
 }
 
 /*
@@ -246,7 +259,6 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
 	struct task_struct *tsk = current;
 	struct ring_buffer_event *event = NULL;
 	struct trace_buffer *buffer = NULL;
-	struct blk_io_trace *t;
 	unsigned long flags = 0;
 	unsigned long *sequence;
 	unsigned int trace_ctx = 0;
@@ -278,20 +290,21 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
 		return;
 	cpu = raw_smp_processor_id();
 
-	trace_len = sizeof(*t) + pdu_len + cgid_len;
 	if (blk_tracer) {
 		tracing_record_cmdline(current);
 
 		buffer = blk_tr->array_buffer.buffer;
 		trace_ctx = tracing_gen_ctx_flags(0);
+		trace_len = sizeof(struct blk_io_trace) + pdu_len + cgid_len;
 		event = trace_buffer_lock_reserve(buffer, TRACE_BLK,
 						  trace_len, trace_ctx);
 		if (!event)
 			return;
-		t = ring_buffer_event_data(event);
 
-		record_blktrace_event(t, pid, cpu, sector, bytes, what, bt->dev,
-				      error, cgid, cgid_len, pdu_data, pdu_len);
+		record_blktrace_event(ring_buffer_event_data(event),
+				      pid, cpu, sector, bytes, what, bt->dev,
+				      error, cgid, cgid_len, pdu_data,
+				      pdu_len);
 
 		trace_buffer_unlock_commit(blk_tr, buffer, event, trace_ctx);
 		return;
@@ -306,19 +319,10 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
 	 * from coming in and stepping on our toes.
 	 */
 	local_irq_save(flags);
-	t = relay_reserve(bt->rchan, trace_len);
-	if (t) {
-		sequence = per_cpu_ptr(bt->sequence, cpu);
-
-		t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION;
-		t->sequence = ++(*sequence);
-		t->time = ktime_to_ns(ktime_get());
-
-		record_blktrace_event(t, pid, cpu, sector, bytes, what,
-				      bt->dev, error, cgid, cgid_len,
-				      pdu_data, pdu_len);
-	}
-
+	sequence = per_cpu_ptr(bt->sequence, cpu);
+	(*sequence)++;
+	relay_blktrace_event(bt, *sequence, pid, cpu, sector, bytes, what,
+			     error, cgid, cgid_len, pdu_data, pdu_len);
 	local_irq_restore(flags);
 }
 
-- 
2.51.0