Re: [PATCH] Configurable Magic Sysrq
From: Jan Kara
Date: Fri Oct 29 2004 - 08:39:24 EST
> Andrew Morton <akpm@xxxxxxxx> writes:
>
> > Jan Kara <jack@xxxxxxx> wrote:
> >>
> >> I know about a few people who would like to use some functionality of
> >> the Magic Sysrq but don't want to enable all the functions it provides.
> >
> > That's a new one. Can you tell us more about why people want to do such a
> > thing?
> >
> >> So I wrote a patch which should allow them to do so. It allows to
> >> configure available functions of Sysrq via /proc/sys/kernel/sysrq (the
> >> interface is backward compatible). If you think it's useful then use it :)
> >> Andrew, do you think it can go into mainline or it's just an overdesign?
> >
> > Patch looks reasonable - we just need to decide whether the requirement
> > warrants its inclusion.
> >
> > There have been a few changes in the sysrq code since 2.6.9 and there are
> > more changes queued up in -mm. The patch applies OK, but it'll need
> > checking and redoing. There's a new `sysrq-f' command in the pipeline
> > which causes a manual oom-killer call.
>
> See also the patch I just posted to lkml.
OK, Andrew, are you accepting the patch? The sysrq should probably go
into SYSRQ_ENABLE_SIGNAL group...
> I also thought of an improved way of selecting keys to enable.
> Instead of an arbitrary bitmask, would it be possible to simply list
> the keys you want to enable, such as "echo sku > /proc/sys/kernel/sysrq"?
That would be possible of course but you'd have to do your own parsing
in kernel and you are not supposed to change the sysrq setting often - usually
just compute your favourite number, put it into boot scripts and you're
done. So I'm not convinced it's useful very much. The attached patch is
against 2.6.10-rc1-mm1 (I also added poweroff to SYSRQ_ENABLE_BOOT group
of functions).
Honza
--
Jan Kara <jack@xxxxxxx>
SuSE CR Labs
Implement enabling of specific sysrq functions.
Signed-off-by: Jan Kara <jack@xxxxxxx>
diff -ru linux-2.6.10-rc1-mm1/Documentation/sysrq.txt linux-2.6.10-rc1-mm1-sysrq/Documentation/sysrq.txt
--- linux-2.6.10-rc1-mm1/Documentation/sysrq.txt 2004-10-29 14:43:29.828759600 +0200
+++ linux-2.6.10-rc1-mm1-sysrq/Documentation/sysrq.txt 2004-10-29 15:05:41.415327672 +0200
@@ -10,13 +10,28 @@
* How do I enable the magic SysRq key?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
You need to say "yes" to 'Magic SysRq key (CONFIG_MAGIC_SYSRQ)' when
-configuring the kernel. When running on a kernel with SysRq compiled in, it
-may be DISABLED at run-time using following command:
+configuring the kernel. When running a kernel with SysRq compiled in,
+/proc/sys/kernel/sysrq controls the functions allowed to be invoked via
+the SysRq key. By default the file contains 1 which means that every
+possible SysRq request is allowed (in older versions SysRq was disabled
+by default, and you were required to specifically enable it at run-time
+but this is not the case any more). Here is the list of possible values
+in /proc/sys/kernel/sysrq:
+ 0 - disable sysrq completely
+ 1 - enable all functions of sysrq
+ >1 - bitmask of allowed sysrq functions (see below for detailed function
+ description):
+ 2 - enable control of console logging level
+ 4 - enable control of keyboard (SAK, unraw)
+ 8 - enable debugging dumps of processes etc.
+ 16 - enable sync command
+ 32 - enable remount read-only
+ 64 - enable signalling of processes (term, kill, oom-kill)
+ 128 - allow reboot/poweroff
+ 256 - allow entering KGDB via sysrq
- echo "0" > /proc/sys/kernel/sysrq
-
-Note that previous versions disabled sysrq by default, and you were required
-to specifically enable it at run-time. That is not the case any longer.
+You can set the value in the file by the following command:
+ echo "number" >/proc/sys/kernel/sysrq
* How do I use the magic SysRq key?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
diff -ru linux-2.6.10-rc1-mm1/drivers/char/sysrq.c linux-2.6.10-rc1-mm1-sysrq/drivers/char/sysrq.c
--- linux-2.6.10-rc1-mm1/drivers/char/sysrq.c 2004-10-29 14:43:33.399216808 +0200
+++ linux-2.6.10-rc1-mm1-sysrq/drivers/char/sysrq.c 2004-10-29 14:59:08.513057896 +0200
@@ -35,6 +35,15 @@
#include <linux/spinlock.h>
#include <asm/ptrace.h>
+
+extern void reset_vc(unsigned int);
+
+/* Whether we react on sysrq keys or just ignore them */
+int sysrq_enabled = 1;
+
+/* Machine specific power off function */
+void (*sysrq_power_off)(void);
+
#ifdef CONFIG_KGDB_SYSRQ
#define GDB_OP &kgdb_op
@@ -48,21 +57,13 @@
.handler = kgdb_sysrq,
.help_msg = "kGdb|Fgdb",
.action_msg = "Debug breakpoint\n",
+ .enable_mask = SYSRQ_ENABLE_BREAKPOINT,
};
#else
#define GDB_OP NULL
#endif
-
-extern void reset_vc(unsigned int);
-
-/* Whether we react on sysrq keys or just ignore them */
-int sysrq_enabled = 1;
-
-/* Machine specific power off function */
-void (*sysrq_power_off)(void);
-
/* Loglevel sysrq handler */
static void sysrq_handle_loglevel(int key, struct pt_regs *pt_regs,
struct tty_struct *tty)
@@ -77,6 +78,7 @@
.handler = sysrq_handle_loglevel,
.help_msg = "loglevel0-8",
.action_msg = "Changing Loglevel",
+ .enable_mask = SYSRQ_ENABLE_LOG,
};
@@ -93,6 +95,7 @@
.handler = sysrq_handle_SAK,
.help_msg = "saK",
.action_msg = "SAK",
+ .enable_mask = SYSRQ_ENABLE_KEYBOARD,
};
#endif
@@ -110,6 +113,7 @@
.handler = sysrq_handle_unraw,
.help_msg = "unRaw",
.action_msg = "Keyboard mode set to XLATE",
+ .enable_mask = SYSRQ_ENABLE_KEYBOARD,
};
#endif /* CONFIG_VT */
@@ -124,6 +128,7 @@
.handler = sysrq_handle_reboot,
.help_msg = "reBoot",
.action_msg = "Resetting",
+ .enable_mask = SYSRQ_ENABLE_BOOT,
};
static void sysrq_handle_sync(int key, struct pt_regs *pt_regs,
@@ -136,6 +141,7 @@
.handler = sysrq_handle_sync,
.help_msg = "Sync",
.action_msg = "Emergency Sync",
+ .enable_mask = SYSRQ_ENABLE_SYNC,
};
static void sysrq_handle_mountro(int key, struct pt_regs *pt_regs,
@@ -148,6 +154,7 @@
.handler = sysrq_handle_mountro,
.help_msg = "Unmount",
.action_msg = "Emergency Remount R/O",
+ .enable_mask = SYSRQ_ENABLE_REMOUNT,
};
/* END SYNC SYSRQ HANDLERS BLOCK */
@@ -165,6 +172,7 @@
.handler = sysrq_handle_showregs,
.help_msg = "showPc",
.action_msg = "Show Regs",
+ .enable_mask = SYSRQ_ENABLE_DUMP,
};
@@ -177,6 +185,7 @@
.handler = sysrq_handle_showstate,
.help_msg = "showTasks",
.action_msg = "Show State",
+ .enable_mask = SYSRQ_ENABLE_DUMP,
};
@@ -189,6 +198,7 @@
.handler = sysrq_handle_showmem,
.help_msg = "showMem",
.action_msg = "Show Memory",
+ .enable_mask = SYSRQ_ENABLE_DUMP,
};
/* SHOW SYSRQ HANDLERS BLOCK */
@@ -219,6 +229,7 @@
.handler = sysrq_handle_term,
.help_msg = "tErm",
.action_msg = "Terminate All Tasks",
+ .enable_mask = SYSRQ_ENABLE_SIGNAL,
};
static void sysrq_handle_moom(int key, struct pt_regs *pt_regs,
@@ -231,6 +242,7 @@
.handler = sysrq_handle_moom,
.help_msg = "Full",
.action_msg = "Manual OOM execution",
+ .enable_mask = SYSRQ_ENABLE_SIGNAL,
};
static void sysrq_handle_kill(int key, struct pt_regs *pt_regs,
@@ -243,6 +255,7 @@
.handler = sysrq_handle_kill,
.help_msg = "kIll",
.action_msg = "Kill All Tasks",
+ .enable_mask = SYSRQ_ENABLE_SIGNAL,
};
/* END SIGNAL SYSRQ HANDLERS BLOCK */
@@ -362,9 +375,13 @@
op_p = __sysrq_get_key_op(key);
if (op_p) {
- printk ("%s\n", op_p->action_msg);
- console_loglevel = orig_log_level;
- op_p->handler(key, pt_regs, tty);
+ if (sysrq_enabled == 1 || sysrq_enabled & op_p->enable_mask) {
+ printk ("%s\n", op_p->action_msg);
+ console_loglevel = orig_log_level;
+ op_p->handler(key, pt_regs, tty);
+ }
+ else
+ printk("This sysrq operation is disabled.\n");
} else {
printk("HELP : ");
/* Only print the help msg once per handler */
diff -ru linux-2.6.10-rc1-mm1/include/linux/sysrq.h linux-2.6.10-rc1-mm1-sysrq/include/linux/sysrq.h
--- linux-2.6.10-rc1-mm1/include/linux/sysrq.h 2004-10-18 23:53:06.000000000 +0200
+++ linux-2.6.10-rc1-mm1-sysrq/include/linux/sysrq.h 2004-10-29 15:00:57.528485032 +0200
@@ -16,10 +16,22 @@
struct pt_regs;
struct tty_struct;
+/* Possible values of bitmask for enabling sysrq functions */
+/* 0x0001 is reserved for enable everything */
+#define SYSRQ_ENABLE_LOG 0x0002
+#define SYSRQ_ENABLE_KEYBOARD 0x0004
+#define SYSRQ_ENABLE_DUMP 0x0008
+#define SYSRQ_ENABLE_SYNC 0x0010
+#define SYSRQ_ENABLE_REMOUNT 0x0020
+#define SYSRQ_ENABLE_SIGNAL 0x0040
+#define SYSRQ_ENABLE_BOOT 0x0080
+#define SYSRQ_ENABLE_BREAKPOINT 0x0100
+
struct sysrq_key_op {
void (*handler)(int, struct pt_regs *, struct tty_struct *);
char *help_msg;
char *action_msg;
+ int enable_mask;
};
#ifdef CONFIG_MAGIC_SYSRQ
diff -ru linux-2.6.10-rc1-mm1/kernel/power/poweroff.c linux-2.6.10-rc1-mm1-sysrq/kernel/power/poweroff.c
--- linux-2.6.10-rc1-mm1/kernel/power/poweroff.c 2004-10-18 23:54:08.000000000 +0200
+++ linux-2.6.10-rc1-mm1-sysrq/kernel/power/poweroff.c 2004-10-29 15:03:01.228679744 +0200
@@ -32,7 +32,8 @@
static struct sysrq_key_op sysrq_poweroff_op = {
.handler = handle_poweroff,
.help_msg = "powerOff",
- .action_msg = "Power Off\n"
+ .action_msg = "Power Off\n",
+ .enable_mask = SYSRQ_ENABLE_BOOT,
};
static int pm_sysrq_init(void)