[PATCH] debug: add sysrq_always_enabled boot option

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.

[bunk@stusta.de: make sysrq_always_enabled_setup() static]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 31 insertions, 6 deletions

diff --git a/drivers/char/sysrq.c b/drivers/char/sysrq.c
index 05810c8d20bc..13935235e066 100644
--- a/drivers/char/sysrq.c
+++ b/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;
+
+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);
+}
+
+static 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)
 {
@@ -379,8 +406,7 @@ void __handle_sysrq(int key, struct tty_struct *tty, int check_mask)
                  * 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);
@@ -414,9 +440,8 @@ void __handle_sysrq(int key, struct tty_struct *tty, int check_mask)
  */
 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);