[PATCH v2 0/2] Add configurable handler to execute a compound action

[PATCH v2 0/2] Add configurable handler to execute a compound action

[Andrzej Pietrasiewicz]

This is a follow-up of this thread:

https://www.spinics.net/lists/linux-input/msg68446.html

It only touches DRM (dri-devel) in such a way that it changes the help
message of sysrq_drm_fb_helper_restore_op, otherwise it is unrelated to DRM.

Patch 2/2 adds a configurable handler to execute a compound action.

Userland might want to execute e.g. 'w' (show blocked tasks), followed
by 's' (sync), followed by 1000 ms delay and then followed by 'c' (crash)
upon a single magic SysRq. Or one might want to execute the famous "Raising
Elephants Is So Utterly Boring" action. This patch adds a configurable
handler, triggered with 'C', for this exact purpose. The user specifies the
composition of the compound action using syntax similar to getopt, where
each letter corresponds to an individual action and a colon followed by a
number corresponds to a delay of that many milliseconds, e.g.:

ws:1000c

or

r:100eis:1000ub

An example of userspace that wants to perform a compound action is
Chrome OS, where SysRq-X (pressed for the second time within a certain
time period from the first time) causes showing the locked tasks, syncing,
waiting a 1000 ms delay and crashing the system.

Since all the slots in the sysrq_key_table[] are already taken or reserved,
patch 1/2 extends it to cover also capital letter versions.

v1..v2:
- used toupper() instead of opencoding it (Jiri Slaby)
- updated help message of sysrq_drm_fb_helper_restore_op (Jiri Slaby)
- used unsigned int for specifying delays (Jiri Slaby)
- improved printed messages formatting (Jiri Slaby)

Andrzej Pietrasiewicz (2):
  tty/sysrq: Extend the sysrq_key_table to cover capital letters
  tty/sysrq: Add configurable handler to execute a compound action

 Documentation/admin-guide/sysrq.rst |  11 +++
 drivers/gpu/drm/drm_fb_helper.c     |   2 +-
 drivers/tty/sysrq.c                 | 129 +++++++++++++++++++++++++++-
 include/linux/sysrq.h               |   1 +
 4 files changed, 140 insertions(+), 3 deletions(-)


base-commit: 9123e3a74ec7b934a4a099e98af6a61c2f80bbf5
-- 
2.17.1

[PATCH v2 1/2] tty/sysrq: Extend the sysrq_key_table to cover capital letters

[Andrzej Pietrasiewicz]

All slots in sysrq_key_table[] are either used, reserved or at least
commented with their intended use. This patch adds capital letter versions
available, which means adding 26 more entries.

For already existing SysRq operations the user presses Alt-SysRq-<key>, and
for the newly added ones Alt-Shift-SysRq-<key>.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
---
 Documentation/admin-guide/sysrq.rst |  2 ++
 drivers/gpu/drm/drm_fb_helper.c     |  2 +-
 drivers/tty/sysrq.c                 | 49 +++++++++++++++++++++++++++--
 3 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/sysrq.rst b/Documentation/admin-guide/sysrq.rst
index e6424d8c5846..67dfa4c29093 100644
--- a/Documentation/admin-guide/sysrq.rst
+++ b/Documentation/admin-guide/sysrq.rst
@@ -79,6 +79,8 @@ On all
 
 		echo t > /proc/sysrq-trigger
 
+The :kbd:`<command key>` is case sensitive.
+
 What are the 'command' keys?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 8697554ccd41..1543d9d10970 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -325,7 +325,7 @@ static void drm_fb_helper_sysrq(int dummy1)
 
 static const struct sysrq_key_op sysrq_drm_fb_helper_restore_op = {
 	.handler = drm_fb_helper_sysrq,
-	.help_msg = "force-fb(V)",
+	.help_msg = "force-fb(v)",
 	.action_msg = "Restore framebuffer console",
 };
 #else
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index a8e39b2cdd55..959f9e121cc6 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -19,6 +19,7 @@
 #include <linux/sched/rt.h>
 #include <linux/sched/debug.h>
 #include <linux/sched/task.h>
+#include <linux/ctype.h>
 #include <linux/interrupt.h>
 #include <linux/mm.h>
 #include <linux/fs.h>
@@ -440,7 +441,7 @@ static const struct sysrq_key_op sysrq_unrt_op = {
 /* Key Operations table and lock */
 static DEFINE_SPINLOCK(sysrq_key_table_lock);
 
-static const struct sysrq_key_op *sysrq_key_table[36] = {
+static const struct sysrq_key_op *sysrq_key_table[62] = {
 	&sysrq_loglevel_op,		/* 0 */
 	&sysrq_loglevel_op,		/* 1 */
 	&sysrq_loglevel_op,		/* 2 */
@@ -497,6 +498,32 @@ static const struct sysrq_key_op *sysrq_key_table[36] = {
 	/* y: May be registered on sparc64 for global register dump */
 	NULL,				/* y */
 	&sysrq_ftrace_dump_op,		/* z */
+	NULL,				/* A */
+	NULL,				/* B */
+	NULL,				/* C */
+	NULL,				/* D */
+	NULL,				/* E */
+	NULL,				/* F */
+	NULL,				/* G */
+	NULL,				/* H */
+	NULL,				/* I */
+	NULL,				/* J */
+	NULL,				/* K */
+	NULL,				/* L */
+	NULL,				/* M */
+	NULL,				/* N */
+	NULL,				/* O */
+	NULL,				/* P */
+	NULL,				/* Q */
+	NULL,				/* R */
+	NULL,				/* S */
+	NULL,				/* T */
+	NULL,				/* U */
+	NULL,				/* V */
+	NULL,				/* W */
+	NULL,				/* X */
+	NULL,				/* Y */
+	NULL,				/* Z */
 };
 
 /* key2index calculation, -1 on invalid index */
@@ -508,6 +535,8 @@ static int sysrq_key_table_key2index(int key)
 		retval = key - '0';
 	else if ((key >= 'a') && (key <= 'z'))
 		retval = key + 10 - 'a';
+	else if ((key >= 'A') && (key <= 'Z'))
+		retval = key + 36 - 'A';
 	else
 		retval = -1;
 	return retval;
@@ -621,6 +650,8 @@ struct sysrq_state {
 	unsigned long key_down[BITS_TO_LONGS(KEY_CNT)];
 	unsigned int alt;
 	unsigned int alt_use;
+	unsigned int shift;
+	unsigned int shift_use;
 	bool active;
 	bool need_reinject;
 	bool reinjecting;
@@ -805,10 +836,20 @@ static bool sysrq_handle_keypress(struct sysrq_state *sysrq,
 		}
 		break;
 
+	case KEY_LEFTSHIFT:
+	case KEY_RIGHTSHIFT:
+		if (!value)
+			sysrq->shift = KEY_RESERVED;
+		else if (value != 2)
+			sysrq->shift = code;
+		break;
+
 	case KEY_SYSRQ:
 		if (value == 1 && sysrq->alt != KEY_RESERVED) {
 			sysrq->active = true;
 			sysrq->alt_use = sysrq->alt;
+			/* either RESERVED (for released) or actual code */
+			sysrq->shift_use = sysrq->shift;
 			/*
 			 * If nothing else will be pressed we'll need
 			 * to re-inject Alt-SysRq keysroke.
@@ -831,8 +872,12 @@ static bool sysrq_handle_keypress(struct sysrq_state *sysrq,
 
 	default:
 		if (sysrq->active && value && value != 2) {
+			unsigned char c = sysrq_xlate[code];
+
 			sysrq->need_reinject = false;
-			__handle_sysrq(sysrq_xlate[code], true);
+			if (sysrq->shift_use != KEY_RESERVED)
+				c = toupper(c);
+			__handle_sysrq(c, true);
 		}
 		break;
 	}
-- 
2.17.1

[PATCH v2 2/2] tty/sysrq: Add configurable handler to execute a compound action

[Andrzej Pietrasiewicz]

Userland might want to execute e.g. 'w' (show blocked tasks), followed
by 's' (sync), followed by 1000 ms delay and then followed by 'c' (crash)
upon a single magic SysRq. Or one might want to execute the famous "Raising
Elephants Is So Utterly Boring" action. This patch adds a configurable
handler, triggered with 'C', for this exact purpose. The user specifies the
composition of the compound action using syntax similar to getopt, where
each letter corresponds to an individual action and a colon followed by a
number corresponds to a delay of that many milliseconds, e.g.:

ws:1000c

or

r:100eis:1000ub

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
---
 Documentation/admin-guide/sysrq.rst |  9 ++++
 drivers/tty/sysrq.c                 | 82 ++++++++++++++++++++++++++++-
 include/linux/sysrq.h               |  1 +
 3 files changed, 91 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/sysrq.rst b/Documentation/admin-guide/sysrq.rst
index 67dfa4c29093..80bdd8bf9636 100644
--- a/Documentation/admin-guide/sysrq.rst
+++ b/Documentation/admin-guide/sysrq.rst
@@ -32,6 +32,7 @@ to 1. Here is the list of possible values in /proc/sys/kernel/sysrq:
          64 =  0x40 - enable signalling of processes (term, kill, oom-kill)
         128 =  0x80 - allow reboot/poweroff
         256 = 0x100 - allow nicing of all RT tasks
+        512 = 0x200 - allow compound action
 
 You can set the value in the file by the following command::
 
@@ -148,6 +149,14 @@ Command	    Function
 
 ``z``	    Dump the ftrace buffer
 
+``C``	    Execute a predefined, compound action. The action is defined with
+	    sysrq.sysrq_compound_action module parameter, whose value contains known
+	    command keys (except ``C`` to prevent recursion). The command keys can
+	    be optionally followed by a colon and a number of milliseconds to wait
+	    after executing the last action. For example:
+
+	    sysrq.sysrq_compound_action=r:100eis:1000ub
+
 ``0``-``9`` Sets the console log level, controlling which kernel messages
             will be printed to your console. (``0``, for example would make
             it so that only emergency messages like PANICs or OOPSes would
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 959f9e121cc6..fec770de325b 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -20,6 +20,7 @@
 #include <linux/sched/debug.h>
 #include <linux/sched/task.h>
 #include <linux/ctype.h>
+#include <linux/delay.h>
 #include <linux/interrupt.h>
 #include <linux/mm.h>
 #include <linux/fs.h>
@@ -438,6 +439,15 @@ static const struct sysrq_key_op sysrq_unrt_op = {
 	.enable_mask	= SYSRQ_ENABLE_RTNICE,
 };
 
+static void sysrq_action_compound(int key);
+
+static struct sysrq_key_op sysrq_action_compound_op = {
+	.handler	= sysrq_action_compound,
+	.help_msg	= "execute-compound-action(C)",
+	.action_msg	= "Execute compound action",
+	.enable_mask	= SYSRQ_ENABLE_COMPOUND,
+};
+
 /* Key Operations table and lock */
 static DEFINE_SPINLOCK(sysrq_key_table_lock);
 
@@ -500,7 +510,7 @@ static const struct sysrq_key_op *sysrq_key_table[62] = {
 	&sysrq_ftrace_dump_op,		/* z */
 	NULL,				/* A */
 	NULL,				/* B */
-	NULL,				/* C */
+	&sysrq_action_compound_op,	/* C */
 	NULL,				/* D */
 	NULL,				/* E */
 	NULL,				/* F */
@@ -633,6 +643,7 @@ EXPORT_SYMBOL(handle_sysrq);
 
 #ifdef CONFIG_INPUT
 static int sysrq_reset_downtime_ms;
+static char *sysrq_compound_action;
 
 /* Simple translation table for the SysRq keys */
 static const unsigned char sysrq_xlate[KEY_CNT] =
@@ -786,6 +797,62 @@ static void sysrq_of_get_keyreset_config(void)
 {
 }
 #endif
+#define SYSRQ_COMPOUND_ACTION_VALIDATE	0
+#define SYSRQ_COMPOUND_ACTION_RUN	1
+
+static int sysrq_process_compound_action(int pass)
+{
+	const char *action = sysrq_compound_action;
+	const struct sysrq_key_op *op_p;
+	int ret;
+	unsigned int delay;
+
+	while (*action) {
+		op_p = __sysrq_get_key_op(*action);
+		if (!op_p)
+			return -EINVAL;
+
+		/* Don't allow calling ourselves recursively */
+		if (op_p == &sysrq_action_compound_op)
+			return -EINVAL;
+
+		if (pass == SYSRQ_COMPOUND_ACTION_RUN)
+			__handle_sysrq(*action, false);
+
+		if (*++action == ':') {
+			ret = sscanf(action++, ":%u", &delay);
+			if (ret < 1) /* we want at least ":[0-9]" => 1 item */
+				return -EINVAL;
+
+			while (*action >= '0' && *action <= '9')
+				++action;
+			if (pass == SYSRQ_COMPOUND_ACTION_RUN)
+				mdelay(delay);
+		}
+	}
+
+	return 0;
+}
+
+static void sysrq_action_compound(int key)
+{
+	if (!sysrq_compound_action) {
+		pr_err("Unconfigured compound action for %s\n",
+		       sysrq_action_compound_op.help_msg);
+
+		return;
+	}
+
+	if (sysrq_process_compound_action(SYSRQ_COMPOUND_ACTION_VALIDATE)) {
+		pr_err("Incorrect compound action %s for %s\n",
+		       sysrq_compound_action,
+		       sysrq_action_compound_op.help_msg);
+
+		return;
+	}
+
+	sysrq_process_compound_action(SYSRQ_COMPOUND_ACTION_RUN);
+}
 
 static void sysrq_reinject_alt_sysrq(struct work_struct *work)
 {
@@ -1077,8 +1144,21 @@ module_param_array_named(reset_seq, sysrq_reset_seq, sysrq_reset_seq,
 
 module_param_named(sysrq_downtime_ms, sysrq_reset_downtime_ms, int, 0644);
 
+module_param(sysrq_compound_action, charp, 0644);
+MODULE_PARM_DESC(sysrq_compound_action,
+	"\tCompound sysrq action to be executed on Alt-Shift-SysRq-C\n"
+	"\tThe compound action definition consists of known SysRq action letters except 'C',\n"
+	"\teach letter can be optionally followed by a colon and a number of milliseconds to wait\n"
+	"\tafter executing the last action.\n"
+	"\tExample:\n"
+	"\tTo unRaw, wait 100ms, tErminate, kIll, Sync, wait 1000ms, Unmount, Boot\n"
+	"\tsysrq.sysrq_compound_action=r:100eis:1000ub");
 #else
 
+{
+}
+
+static void sysrq_action_compound(int key)
 static inline void sysrq_register_handler(void)
 {
 }
diff --git a/include/linux/sysrq.h b/include/linux/sysrq.h
index 3a582ec7a2f1..6df4442f12a9 100644
--- a/include/linux/sysrq.h
+++ b/include/linux/sysrq.h
@@ -28,6 +28,7 @@
 #define SYSRQ_ENABLE_SIGNAL	0x0040
 #define SYSRQ_ENABLE_BOOT	0x0080
 #define SYSRQ_ENABLE_RTNICE	0x0100
+#define SYSRQ_ENABLE_COMPOUND	0x0200
 
 struct sysrq_key_op {
 	void (* const handler)(int);
-- 
2.17.1