linux-kernel - [for-next][PATCH 10/13] tracing: Add trace_seq_pop() and seq_buf

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Message-ID: <20251029144125.122306386@kernel.org>
Date: Wed, 29 Oct 2025 10:40:51 -0400
From: Steven Rostedt <rostedt@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Peter Zijlstra <peterz@...radead.org>,
 Namhyung Kim <namhyung@...nel.org>,
 Takaya Saeki <takayas@...gle.com>,
 Tom Zanussi <zanussi@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>,
 Ian Rogers <irogers@...gle.com>,
 Douglas Raillard <douglas.raillard@....com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Jiri Olsa <jolsa@...nel.org>,
 Adrian Hunter <adrian.hunter@...el.com>,
 Ingo Molnar <mingo@...hat.com>
Subject: [for-next][PATCH 10/13] tracing: Add trace_seq_pop() and seq_buf_pop()

From: Steven Rostedt <rostedt@...dmis.org>

In order to allow an interface to remove an added character from the
trace_seq and seq_buf descriptors, add helper functions trace_seq_pop()
and seq_buf_pop().

Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Takaya Saeki <takayas@...gle.com>
Cc: Tom Zanussi <zanussi@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ian Rogers <irogers@...gle.com>
Cc: Douglas Raillard <douglas.raillard@....com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Ingo Molnar <mingo@...hat.com>
Link: https://lore.kernel.org/20251028231148.594898736@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 include/linux/seq_buf.h   | 17 +++++++++++++++++
 include/linux/trace_seq.h | 13 +++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/include/linux/seq_buf.h b/include/linux/seq_buf.h
index 52791e070506..9f2839e73f8a 100644
--- a/include/linux/seq_buf.h
+++ b/include/linux/seq_buf.h
@@ -149,6 +149,23 @@ static inline void seq_buf_commit(struct seq_buf *s, int num)
 	}
 }
 
+/**
+ * seq_buf_pop - pop off the last written character
+ * @s: the seq_buf handle
+ *
+ * Removes the last written character to the seq_buf @s.
+ *
+ * Returns the last character or -1 if it is empty.
+ */
+static inline int seq_buf_pop(struct seq_buf *s)
+{
+	if (!s->len)
+		return -1;
+
+	s->len--;
+	return (unsigned int)s->buffer[s->len];
+}
+
 extern __printf(2, 3)
 int seq_buf_printf(struct seq_buf *s, const char *fmt, ...);
 extern __printf(2, 0)
diff --git a/include/linux/trace_seq.h b/include/linux/trace_seq.h
index 557780fe1c77..4a0b8c172d27 100644
--- a/include/linux/trace_seq.h
+++ b/include/linux/trace_seq.h
@@ -80,6 +80,19 @@ static inline bool trace_seq_has_overflowed(struct trace_seq *s)
 	return s->full || seq_buf_has_overflowed(&s->seq);
 }
 
+/**
+ * trace_seq_pop - pop off the last written character
+ * @s: trace sequence descriptor
+ *
+ * Removes the last written character to the trace_seq @s.
+ *
+ * Returns the last character or -1 if it is empty.
+ */
+static inline int trace_seq_pop(struct trace_seq *s)
+{
+	return seq_buf_pop(&s->seq);
+}
+
 /*
  * Currently only defined when tracing is enabled.
  */
-- 
2.51.0