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([2001:fb1:db:5c33:ea21:9586:4d37:987d]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ccc9d3bbaesm92010215ad.57.2026.07.12.21.54.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 12 Jul 2026 21:54:08 -0700 (PDT) From: Woradorn Laodhanadhaworn To: rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, linux-kernel-mentees@lists.linux.dev, shuah@kernel.org, skhan@linuxfoundation.org, me@brighamcampbell.com, jkoolstra@xs4all.nl, woradorn.laon@gmail.com Subject: [PATCH v4] tracing: Use seq_buf for string concatenation Date: Mon, 13 Jul 2026 11:52:49 +0700 Message-ID: <20260713045249.69942-1-woradorn.laon@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel-mentees@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In preparation for removing the strlcat API[1], replace the string concatenation logic with a struct seq_buf, which tracks the current position and the remaining space internally. Use seq_buf_str() to NUL-terminate before passing to early_enable_events(). Link: https://github.com/KSPP/linux/issues/370 [1] Signed-off-by: Woradorn Laodhanadhaworn --- v1 -> v2: - Fixed WARN_ON when booting with empty trace_event. v2 -> v3: - Addressed Sashiko's concern about the compound literal backing buffer. - Replaced the compund literal with an explicit declared buffer and pointed seq_buf.buffer to it. This guarantees the backing storage is placed in `.init.data` and reclaimed after boot. v3 -> v4: - Removed typecast a const char* to non const. v1: https://lore.kernel.org/all/20260620175441.223342-1-woradorn.laon@gmail.com v2: https://lore.kernel.org/all/20260622094623.18469-1-woradorn.laon@gmail.com v3: https://lore.kernel.org/all/20260623145147.12145-1-woradorn.laon@gmail.com Sashiko: https://sashiko.dev/#/patchset/20260622094623.18469-1-woradorn.laon%40gmail.com kernel/trace/trace_events.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index c46e623e7e0d..4f5a0e73a89b 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -22,6 +22,7 @@ #include #include #include +#include #include #include @@ -4501,13 +4502,20 @@ extern struct trace_event_call *__start_ftrace_events[]; extern struct trace_event_call *__stop_ftrace_events[]; static char bootup_event_buf[COMMAND_LINE_SIZE] __initdata; +static struct seq_buf bootup_event_seq __initdata = { + .buffer = bootup_event_buf, + .size = sizeof(bootup_event_buf), +}; static __init int setup_trace_event(char *str) { - if (bootup_event_buf[0] != '\0') - strlcat(bootup_event_buf, ",", COMMAND_LINE_SIZE); + if (seq_buf_used(&bootup_event_seq) > 0) + seq_buf_puts(&bootup_event_seq, ","); + + seq_buf_puts(&bootup_event_seq, str); - strlcat(bootup_event_buf, str, COMMAND_LINE_SIZE); + if (seq_buf_has_overflowed(&bootup_event_seq)) + return -ENOMEM; trace_set_ring_buffer_expanded(NULL); disable_tracing_selftest("running event tracing"); @@ -4766,6 +4774,7 @@ static __init int event_trace_enable(void) */ __trace_early_add_events(tr); + seq_buf_str(&bootup_event_seq); early_enable_events(tr, bootup_event_buf, false); trace_printk_start_comm(); @@ -4794,6 +4803,7 @@ static __init int event_trace_enable_again(void) if (!tr) return -ENODEV; + seq_buf_str(&bootup_event_seq); early_enable_events(tr, bootup_event_buf, true); return 0; -- 2.43.0