panic: add note that 'panic_print' parameter is deprecated

Just like for 'panic_print's systcl interface, add similar note for setup
of kernel cmdline parameter and parameter under /sys/module/kernel/.

Also add __core_param_cb() macro, which enables to add special get/set
operation for a kernel parameter.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Feng Tang <[email protected]>
Suggested-by: Petr Mladek <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Cc: Askar Safin <[email protected]>
Cc: John Ogness <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Lance Yang <[email protected]>
Cc: "Paul E . McKenney" <[email protected]>
Cc: Steven Rostedt <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

include/linux/moduleparam.h

@@ -349,6 +349,19 @@ static inline void kernel_param_unlock(struct module *mod)
 	__module_param_call("", name, &param_ops_##type, &var, perm,	\
 			    -1, KERNEL_PARAM_FL_UNSAFE)
 
+/**
+ * __core_param_cb - similar like core_param, with a set/get ops instead of type.
+ * @name: the name of the cmdline and sysfs parameter (often the same as var)
+ * @var: the variable
+ * @ops: the set & get operations for this parameter.
+ * @perm: visibility in sysfs
+ *
+ * Ideally this should be called 'core_param_cb', but the name has been
+ * used for module core parameter, so add the '__' prefix
+ */
+#define __core_param_cb(name, ops, arg, perm) \
+	__module_param_call("", name, ops, arg, perm, -1, 0)
+
 #endif /* !MODULE */
 
 /**

kernel/panic.c

@@ -937,12 +937,29 @@ EXPORT_SYMBOL(__stack_chk_fail);
 #endif
 
 core_param(panic, panic_timeout, int, 0644);
-core_param(panic_print, panic_print, ulong, 0644);
 core_param(pause_on_oops, pause_on_oops, int, 0644);
 core_param(panic_on_warn, panic_on_warn, int, 0644);
 core_param(crash_kexec_post_notifiers, crash_kexec_post_notifiers, bool, 0644);
 core_param(panic_console_replay, panic_console_replay, bool, 0644);
 
+static int panic_print_set(const char *val, const struct kernel_param *kp)
+{
+	pr_info_once("Kernel: 'panic_print' parameter will be obsoleted by both 'panic_sys_info' and 'panic_console_replay'\n");
+	return  param_set_ulong(val, kp);
+}
+
+static int panic_print_get(char *val, const struct kernel_param *kp)
+{
+	pr_info_once("Kernel: 'panic_print' parameter will be obsoleted by both 'panic_sys_info' and 'panic_console_replay'\n");
+	return  param_get_ulong(val, kp);
+}
+
+static const struct kernel_param_ops panic_print_ops = {
+	.set	= panic_print_set,
+	.get	= panic_print_get,
+};
+__core_param_cb(panic_print, &panic_print_ops, &panic_print, 0644);
+
 static int __init oops_setup(char *s)
 {
 	if (!s)