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Subject[patch] debug: add sysrq_always_enabled boot option
Subject: [patch] debug: add sysrq_always_enabled boot option
From: Ingo Molnar <mingo@elte.hu>

most distributions enable sysrq support but set it to 0 by default. Add
a sysrq_always_enabled boot option to always-enable sysrq keys. Useful
for debugging - without having to modify the disribution's config files
(which might not be possible if the kernel is on a live CD, etc.).

also, while at it, clean up the sysrq interfaces.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
Documentation/kernel-parameters.txt | 6 +++++
drivers/char/sysrq.c | 37 ++++++++++++++++++++++++++++++------
drivers/char/viocons.c | 10 +++------
include/linux/sysrq.h | 22 +++++++++++++++++----
kernel/sysctl.c | 3 --
5 files changed, 60 insertions(+), 18 deletions(-)

Index: linux/Documentation/kernel-parameters.txt
===================================================================
--- linux.orig/Documentation/kernel-parameters.txt
+++ linux/Documentation/kernel-parameters.txt
@@ -1637,6 +1637,12 @@ and is between 256 and 4096 characters.
sym53c416= [HW,SCSI]
See header of drivers/scsi/sym53c416.c.

+ sysrq_always_enabled
+ [KNL]
+ Ignore sysrq setting - this boot parameter will
+ neutralize any effect of /proc/sys/kernel/sysrq.
+ Useful for debugging.
+
t128= [HW,SCSI]
See header of drivers/scsi/t128.c.

Index: linux/drivers/char/sysrq.c
===================================================================
--- linux.orig/drivers/char/sysrq.c
+++ linux/drivers/char/sysrq.c
@@ -41,7 +41,34 @@
#include <asm/irq_regs.h>

/* Whether we react on sysrq keys or just ignore them */
-int sysrq_enabled = 1;
+int __read_mostly __sysrq_enabled = 1;
+
+static int __read_mostly sysrq_always_enabled = 0;
+
+int sysrq_on(void)
+{
+ return __sysrq_enabled || sysrq_always_enabled;
+}
+
+/*
+ * A value of 1 means 'all', other nonzero values are an op mask:
+ */
+static inline int sysrq_on_mask(int mask)
+{
+ return sysrq_always_enabled || __sysrq_enabled == 1 ||
+ (__sysrq_enabled & mask);
+}
+
+int __init sysrq_always_enabled_setup(char *str)
+{
+ sysrq_always_enabled = 1;
+ printk(KERN_INFO "debug: sysrq always enabled.\n");
+
+ return 1;
+}
+
+__setup("sysrq_always_enabled", sysrq_always_enabled_setup);
+

static void sysrq_handle_loglevel(int key, struct tty_struct *tty)
{
@@ -383,8 +410,7 @@ void __handle_sysrq(int key, struct tty_
* Should we check for enabled operations (/proc/sysrq-trigger
* should not) and is the invoked operation enabled?
*/
- if (!check_mask || sysrq_enabled == 1 ||
- (sysrq_enabled & op_p->enable_mask)) {
+ if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
printk("%s\n", op_p->action_msg);
console_loglevel = orig_log_level;
op_p->handler(key, tty);
@@ -418,9 +444,8 @@ void __handle_sysrq(int key, struct tty_
*/
void handle_sysrq(int key, struct tty_struct *tty)
{
- if (!sysrq_enabled)
- return;
- __handle_sysrq(key, tty, 1);
+ if (sysrq_on())
+ __handle_sysrq(key, tty, 1);
}
EXPORT_SYMBOL(handle_sysrq);

Index: linux/drivers/char/viocons.c
===================================================================
--- linux.orig/drivers/char/viocons.c
+++ linux/drivers/char/viocons.c
@@ -61,10 +61,7 @@
static DEFINE_SPINLOCK(consolelock);
static DEFINE_SPINLOCK(consoleloglock);

-#ifdef CONFIG_MAGIC_SYSRQ
static int vio_sysrq_pressed;
-extern int sysrq_enabled;
-#endif

#define VIOCHAR_NUM_BUF 16

@@ -936,8 +933,10 @@ static void vioHandleData(struct HvLpEve
*/
num_pushed = 0;
for (index = 0; index < cevent->len; index++) {
-#ifdef CONFIG_MAGIC_SYSRQ
- if (sysrq_enabled) {
+ /*
+ * Will be optimized away if !CONFIG_MAGIC_SYSRQ:
+ */
+ if (sysrq_on()) {
/* 0x0f is the ascii character for ^O */
if (cevent->data[index] == '\x0f') {
vio_sysrq_pressed = 1;
@@ -956,7 +955,6 @@ static void vioHandleData(struct HvLpEve
continue;
}
}
-#endif
/*
* The sysrq sequence isn't included in this check if
* sysrq is enabled and compiled into the kernel because
Index: linux/include/linux/sysrq.h
===================================================================
--- linux.orig/include/linux/sysrq.h
+++ linux/include/linux/sysrq.h
@@ -37,23 +37,37 @@ struct sysrq_key_op {

#ifdef CONFIG_MAGIC_SYSRQ

+extern int sysrq_on(void);
+
+/*
+ * Do not use this one directly:
+ */
+extern int __sysrq_enabled;
+
/* Generic SysRq interface -- you may call it from any device driver, supplying
* ASCII code of the key, pointer to registers and kbd/tty structs (if they
* are available -- else NULL's).
*/

-void handle_sysrq(int, struct tty_struct *);
-void __handle_sysrq(int, struct tty_struct *, int check_mask);
-int register_sysrq_key(int, struct sysrq_key_op *);
-int unregister_sysrq_key(int, struct sysrq_key_op *);
+void handle_sysrq(int key, struct tty_struct *tty);
+void __handle_sysrq(int key, struct tty_struct *tty, int check_mask);
+int register_sysrq_key(int key, struct sysrq_key_op *op);
+int unregister_sysrq_key(int key, struct sysrq_key_op *op);
struct sysrq_key_op *__sysrq_get_key_op(int key);

#else

+static inline int sysrq_on(void)
+{
+ return 0;
+}
static inline int __reterr(void)
{
return -EINVAL;
}
+static inline void handle_sysrq(int key, struct tty_struct *tty)
+{
+}

#define register_sysrq_key(ig,nore) __reterr()
#define unregister_sysrq_key(ig,nore) __reterr()
Index: linux/kernel/sysctl.c
===================================================================
--- linux.orig/kernel/sysctl.c
+++ linux/kernel/sysctl.c
@@ -65,7 +65,6 @@ extern int sysctl_overcommit_memory;
extern int sysctl_overcommit_ratio;
extern int sysctl_panic_on_oom;
extern int max_threads;
-extern int sysrq_enabled;
extern int core_uses_pid;
extern int suid_dumpable;
extern char core_pattern[];
@@ -697,7 +696,7 @@ static ctl_table kern_table[] = {
{
.ctl_name = KERN_SYSRQ,
.procname = "sysrq",
- .data = &sysrq_enabled,
+ .data = &__sysrq_enabled,
.maxlen = sizeof (int),
.mode = 0644,
.proc_handler = &proc_dointvec,
-
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