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Message-ID: <20251019100605.1.I095f1e2c6c27f9f4de0b4841f725f356c643a13f@changeid>
Date: Sun, 19 Oct 2025 10:06:14 -0700
From: Douglas Anderson <dianders@...omium.org>
To: linux-kernel@...r.kernel.org
Cc: Andrew Chant <achant@...gle.com>,
Douglas Anderson <dianders@...omium.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Brian Gerst <brgerst@...il.com>,
Christian Brauner <brauner@...nel.org>,
Francesco Valla <francesco@...la.it>,
Geert Uytterhoeven <geert+renesas@...der.be>,
Guo Weikang <guoweikang.kernel@...il.com>,
Huacai Chen <chenhuacai@...nel.org>,
Jan Hendrik Farr <kernel@...rr.cc>,
Jeff Xu <jeffxu@...omium.org>,
Kees Cook <kees@...nel.org>,
Masahiro Yamada <masahiroy@...nel.org>,
Michal Koutný <mkoutny@...e.com>,
Miguel Ojeda <ojeda@...nel.org>,
"Mike Rapoport (Microsoft)" <rppt@...nel.org>,
Nathan Chancellor <nathan@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Randy Dunlap <rdunlap@...radead.org>,
Shakeel Butt <shakeel.butt@...ux.dev>,
Tejun Heo <tj@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
"Uladzislau Rezki (Sony)" <urezki@...il.com>
Subject: [PATCH] init/main.c: Wrap long kernel cmdline when printing to logs
The kernel cmdline length is allowed to be longer than what printk can
handle. When this happens the cmdline that's printed to the kernel
ring buffer at bootup is cutoff and some kernel cmdline options are
"hidden" from the logs. This undercuts the usefulness of the log
message.
Add wrapping to the printout. Allow wrapping to be set lower by a
Kconfig knob "CONFIG_CMDLINE_LOG_WRAP_IDEAL_LEN". By default, the
wrapping is set to 1021 characters, which is measured to be the
current maximum that pr_notice() can handle. Anyone whose cmdline
isn't being cut off today should see no difference in log output.
Wrapping is based on spaces, ignoring quotes. All lines are prefixed
with "Kernel command line: " and lines that are not the last line have
a " \" suffix added to them. The prefix and suffix count towards the
line length for wrapping purposes. The ideal length will be exceeded
if no appropriate place to wrap is found.
Signed-off-by: Douglas Anderson <dianders@...omium.org>
---
init/Kconfig | 10 +++++++
init/main.c | 83 +++++++++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 92 insertions(+), 1 deletion(-)
diff --git a/init/Kconfig b/init/Kconfig
index cab3ad28ca49..905b2ece4127 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1512,6 +1512,16 @@ config BOOT_CONFIG_EMBED_FILE
This bootconfig will be used if there is no initrd or no other
bootconfig in the initrd.
+config CMDLINE_LOG_WRAP_IDEAL_LEN
+ int "Length to try to wrap the cmdline when logged at boot"
+ default 1021
+ range 40 1021
+ help
+ At boot time, the kernel command line is logged to the console.
+ It will attempt to be wrapped at this many characters. If there
+ are more than this many non-space characters in a row, log lines
+ may exceed this ideal maximum length.
+
config INITRAMFS_PRESERVE_MTIME
bool "Preserve cpio archive mtimes in initramfs"
depends on BLK_DEV_INITRD
diff --git a/init/main.c b/init/main.c
index 07a3116811c5..0adc1575a2cb 100644
--- a/init/main.c
+++ b/init/main.c
@@ -906,6 +906,87 @@ static void __init early_numa_node_init(void)
#endif
}
+#define KERNEL_CMDLINE_PREFIX "Kernel command line: "
+#define KERNEL_CMDLINE_PREFIX_LEN (sizeof(KERNEL_CMDLINE_PREFIX) - 1)
+#define KERNEL_CMDLINE_CONTINUATION " \\"
+#define KERNEL_CMDLINE_CONTINUATION_LEN (sizeof(KERNEL_CMDLINE_CONTINUATION) - 1)
+
+#define IDEAL_CMDLINE_LEN (CONFIG_CMDLINE_LOG_WRAP_IDEAL_LEN - \
+ KERNEL_CMDLINE_PREFIX_LEN)
+#define IDEAL_CMDLINE_SPLIT_LEN (IDEAL_CMDLINE_LEN - KERNEL_CMDLINE_CONTINUATION_LEN)
+
+/**
+ * print_kernel_cmdline() - Print the kernel cmdline with wrapping.
+ * @cmdline: The cmdline to print.
+ *
+ * Print the kernel command line, trying to wrap based on the Kconfig knob
+ * CONFIG_CMDLINE_LOG_WRAP_IDEAL_LEN.
+ *
+ * Wrapping is based on spaces, ignoring quotes. All lines are prefixed
+ * with "Kernel command line: " and lines that are not the last line have
+ * a " \" suffix added to them. The prefix and suffix count towards the
+ * line length for wrapping purposes. The ideal length will be exceeded
+ * if no appropriate place to wrap is found.
+ *
+ * Example output if CONFIG_CMDLINE_LOG_WRAP_IDEAL_LEN is 40:
+ * Kernel command line: loglevel=7 \
+ * Kernel command line: init=/sbin/init \
+ * Kernel command line: root=PARTUUID=8c3efc1a-768b-6642-8d0c-89eb782f19f0/PARTNROFF=1 \
+ * Kernel command line: rootwait ro \
+ * Kernel command line: my_quoted_arg="The \
+ * Kernel command line: quick brown fox \
+ * Kernel command line: jumps over the \
+ * Kernel command line: lazy dog."
+ */
+static void print_kernel_cmdline(const char *cmdline)
+{
+ size_t len = strlen(cmdline);
+
+ while (len > IDEAL_CMDLINE_LEN) {
+ const char *first_space;
+ const char *prev_cutoff;
+ const char *cutoff;
+ int to_print;
+ size_t used;
+
+ /* Find the last ' ' that wouldn't make the line too long */
+ prev_cutoff = NULL;
+ cutoff = cmdline;
+ while (true) {
+ cutoff = strchr(cutoff + 1, ' ');
+ if (!cutoff || cutoff - cmdline > IDEAL_CMDLINE_SPLIT_LEN)
+ break;
+ prev_cutoff = cutoff;
+ }
+ if (prev_cutoff)
+ cutoff = prev_cutoff;
+ else if (!cutoff)
+ break;
+
+ /* Find the beginning and end of the string of spaces */
+ first_space = cutoff;
+ while (first_space > cmdline && first_space[-1] == ' ')
+ first_space--;
+ to_print = first_space - cmdline;
+ while (*cutoff == ' ')
+ cutoff++;
+ used = cutoff - cmdline;
+
+ /* If the whole string is used, break and do the final printout */
+ if (len == used)
+ break;
+
+ if (to_print)
+ pr_notice("%s%.*s%s\n", KERNEL_CMDLINE_PREFIX,
+ to_print, cmdline, KERNEL_CMDLINE_CONTINUATION);
+
+ len -= used;
+ cmdline += used;
+ }
+ if (len)
+ pr_notice("%s%s\n", KERNEL_CMDLINE_PREFIX, cmdline);
+}
+
asmlinkage __visible __init __no_sanitize_address __noreturn __no_stack_protector
void start_kernel(void)
{
@@ -942,7 +1023,7 @@ void start_kernel(void)
early_numa_node_init();
boot_cpu_hotplug_init();
- pr_notice("Kernel command line: %s\n", saved_command_line);
+ print_kernel_cmdline(saved_command_line);
/* parameters may set static keys */
parse_early_param();
after_dashes = parse_args("Booting kernel",
--
2.51.0.858.gf9c4a03a3a-goog
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