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Message-ID: <95295969cda8464d95339b2a7ecaefe1d865f8d8.1763492585.git.chris@chrisdown.name>
Date: Wed, 19 Nov 2025 03:07:46 +0800
From: Chris Down <chris@...isdown.name>
To: Petr Mladek <pmladek@...e.com>
Cc: linux-kernel@...r.kernel.org,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Sergey Senozhatsky <senozhatsky@...omium.org>,
Steven Rostedt <rostedt@...dmis.org>,
John Ogness <john.ogness@...utronix.de>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
Tony Lindgren <tony.lindgren@...ux.intel.com>, kernel-team@...com
Subject: [PATCH v7 10/13] printk: Add sysctl interface to set global loglevels
Introduce two new sysctl interfaces for configuring global loglevels:
- kernel.console_loglevel: Sets the global console loglevel, determining
the minimum priority of messages printed to consoles. Messages with a
loglevel lower than this value will be printed.
- kernel.default_message_loglevel: Sets the default loglevel for
messages that do not specify an explicit loglevel.
The kernel.printk sysctl was previously used to set multiple loglevel
parameters simultaneously, but it was confusing and lacked proper
validation. By introducing these dedicated sysctl interfaces, we provide
a clearer and more granular way to configure the loglevels.
Signed-off-by: Petr Mladek <pmladek@...e.com>
Signed-off-by: Chris Down <chris@...isdown.name>
---
Documentation/admin-guide/sysctl/kernel.rst | 17 ++++++-
include/linux/sysctl.h | 7 +++
kernel/printk/sysctl.c | 52 +++++++++++++++++++++
kernel/sysctl.c | 18 +++----
4 files changed, 84 insertions(+), 10 deletions(-)
diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index f3ee807b5d8b..043d5f663b7d 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -1079,6 +1079,20 @@ otherwise the 'doze' mode will be used.
==============================================================
+Some of these settings may be overridden per-console, see
+Documentation/admin-guide/per-console-loglevel.rst. See ``man 2 syslog`` for
+more information on the different loglevels.
+
+console_loglevel
+================
+
+Messages with a higher priority than this will be printed to consoles.
+
+default_message_loglevel
+========================
+
+Messages without an explicit priority will be printed with this priority.
+
printk
======
@@ -1087,8 +1101,7 @@ The four values in printk denote: ``console_loglevel``,
``default_console_loglevel`` respectively.
These values influence printk() behavior when printing or
-logging error messages. See '``man 2 syslog``' for more info on
-the different loglevels.
+logging error messages.
======================== =====================================
console_loglevel messages with a higher priority than
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 92e9146b1104..c2f72d172f64 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -235,6 +235,13 @@ extern struct ctl_table_header *register_sysctl_mount_point(const char *path);
void do_sysctl_args(void);
bool sysctl_is_alias(char *param);
+int do_proc_dointvec_conv(bool *negp, unsigned long *lvalp, int *valp,
+ int write, void *data);
+int do_proc_dointvec(const struct ctl_table *table, int write,
+ void *buffer, size_t *lenp, loff_t *ppos,
+ int (*conv)(bool *negp, unsigned long *lvalp, int *valp,
+ int write, void *data),
+ void *data);
int do_proc_douintvec(const struct ctl_table *table, int write,
void *buffer, size_t *lenp, loff_t *ppos,
int (*conv)(unsigned long *lvalp,
diff --git a/kernel/printk/sysctl.c b/kernel/printk/sysctl.c
index da77f3f5c1fe..feec6cf939af 100644
--- a/kernel/printk/sysctl.c
+++ b/kernel/printk/sysctl.c
@@ -11,6 +11,9 @@
static const int ten_thousand = 10000;
+static int min_msg_loglevel = LOGLEVEL_EMERG;
+static int max_msg_loglevel = LOGLEVEL_DEBUG;
+
static int proc_dointvec_minmax_sysadmin(const struct ctl_table *table, int write,
void *buffer, size_t *lenp, loff_t *ppos)
{
@@ -20,6 +23,39 @@ static int proc_dointvec_minmax_sysadmin(const struct ctl_table *table, int writ
return proc_dointvec_minmax(table, write, buffer, lenp, ppos);
}
+static int do_proc_dointvec_console_loglevel(bool *negp, unsigned long *lvalp,
+ int *valp,
+ int write, void *data)
+{
+ int level, ret;
+
+ /*
+ * If writing, first do so via a temporary local int so we can
+ * bounds-check it before touching *valp.
+ */
+ int *intp = write ? &level : valp;
+
+ ret = do_proc_dointvec_conv(negp, lvalp, intp, write, data);
+ if (ret)
+ return ret;
+
+ if (write) {
+ if (level != console_clamp_loglevel(level))
+ return -ERANGE;
+ WRITE_ONCE(*valp, level);
+ }
+
+ return 0;
+}
+
+static int proc_dointvec_console_loglevel(const struct ctl_table *table,
+ int write, void *buffer, size_t *lenp,
+ loff_t *ppos)
+{
+ return do_proc_dointvec(table, write, buffer, lenp, ppos,
+ do_proc_dointvec_console_loglevel, NULL);
+}
+
static const struct ctl_table printk_sysctls[] = {
{
.procname = "printk",
@@ -76,6 +112,22 @@ static const struct ctl_table printk_sysctls[] = {
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_TWO,
},
+ {
+ .procname = "console_loglevel",
+ .data = &console_loglevel,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_console_loglevel,
+ },
+ {
+ .procname = "default_message_loglevel",
+ .data = &default_message_loglevel,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &min_msg_loglevel,
+ .extra2 = &max_msg_loglevel,
+ },
};
void __init printk_sysctl_init(void)
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index cb6196e3fa99..3ed010b8f6b3 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -354,9 +354,9 @@ static void proc_put_char(void **buf, size_t *size, char c)
}
}
-static int do_proc_dointvec_conv(bool *negp, unsigned long *lvalp,
- int *valp,
- int write, void *data)
+int do_proc_dointvec_conv(bool *negp, unsigned long *lvalp,
+ int *valp,
+ int write, void *data)
{
if (write) {
if (*negp) {
@@ -380,6 +380,7 @@ static int do_proc_dointvec_conv(bool *negp, unsigned long *lvalp,
}
return 0;
}
+EXPORT_SYMBOL(do_proc_dointvec_conv);
static int do_proc_douintvec_conv(unsigned long *lvalp,
unsigned int *valp,
@@ -471,15 +472,16 @@ static int __do_proc_dointvec(void *tbl_data, const struct ctl_table *table,
return err;
}
-static int do_proc_dointvec(const struct ctl_table *table, int write,
- void *buffer, size_t *lenp, loff_t *ppos,
- int (*conv)(bool *negp, unsigned long *lvalp, int *valp,
- int write, void *data),
- void *data)
+int do_proc_dointvec(const struct ctl_table *table, int write,
+ void *buffer, size_t *lenp, loff_t *ppos,
+ int (*conv)(bool *negp, unsigned long *lvalp, int *valp,
+ int write, void *data),
+ void *data)
{
return __do_proc_dointvec(table->data, table, write,
buffer, lenp, ppos, conv, data);
}
+EXPORT_SYMBOL(do_proc_dointvec);
static int do_proc_douintvec_w(unsigned int *tbl_data,
const struct ctl_table *table,
--
2.51.2
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