kobject: Make support for uevent_helper optional.

Support for uevent_helper, aka hotplug, is not required on many systems
these days but it can still be enabled via sysfs or sysctl.
Reported-by: Darren Shepherd <darren.s.shepherd@gmail.com>
Signed-off-by: Michael Marineau <mike@marineau.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/Kconfig

 menu "Generic Driver Options"
 
-config UEVENT_HELPER_PATH
-	string "path to uevent helper"
-	default ""
+config UEVENT_HELPER
+	bool "Support for uevent helper"
+	default y
 	help
-	  Path to uevent helper program forked by the kernel for
+	  The uevent helper program is forked by the kernel for
 	  every uevent.
 	  Before the switch to the netlink-based uevent source, this was
 	  used to hook hotplug scripts into kernel device events. It
@@ -15,8 +15,13 @@ config UEVENT_HELPER_PATH
 	  that it creates a high system load, or on smaller systems
 	  it is known to create out-of-memory situations during bootup.
 
-	  To disable user space helper program execution at early boot
-	  time specify an empty string here. This setting can be altered
+config UEVENT_HELPER_PATH
+	string "path to uevent helper"
+	depends on UEVENT_HELPER
+	default ""
+	help
+	  To disable user space helper program execution at by default
+	  specify an empty string here. This setting can still be altered
 	  via /proc/sys/kernel/hotplug or via /sys/kernel/uevent_helper
 	  later at runtime.
 

include/linux/kobject.h

@@ -32,8 +32,10 @@
 #define UEVENT_NUM_ENVP			32	/* number of env pointers */
 #define UEVENT_BUFFER_SIZE		2048	/* buffer for the variables */
 
+#ifdef CONFIG_UEVENT_HELPER
 /* path to the userspace helper executed on an event */
 extern char uevent_helper[];
+#endif
 
 /* counter to tag the uevent, read only except for the kobject core */
 extern u64 uevent_seqnum;

kernel/ksysfs.c

@@ -37,6 +37,7 @@ static ssize_t uevent_seqnum_show(struct kobject *kobj,
 }
 KERNEL_ATTR_RO(uevent_seqnum);
 
+#ifdef CONFIG_UEVENT_HELPER
 /* uevent helper program, used during early boot */
 static ssize_t uevent_helper_show(struct kobject *kobj,
 				  struct kobj_attribute *attr, char *buf)
@@ -56,7 +57,7 @@ static ssize_t uevent_helper_store(struct kobject *kobj,
 	return count;
 }
 KERNEL_ATTR_RW(uevent_helper);
-
+#endif
 
 #ifdef CONFIG_PROFILING
 static ssize_t profiling_show(struct kobject *kobj,
@@ -189,7 +190,9 @@ EXPORT_SYMBOL_GPL(kernel_kobj);
 static struct attribute * kernel_attrs[] = {
 	&fscaps_attr.attr,
 	&uevent_seqnum_attr.attr,
+#ifdef CONFIG_UEVENT_HELPER
 	&uevent_helper_attr.attr,
+#endif
 #ifdef CONFIG_PROFILING
 	&profiling_attr.attr,
 #endif

kernel/sysctl.c

@@ -643,7 +643,7 @@ static struct ctl_table kern_table[] = {
 		.extra2		= &one,
 	},
 #endif
-
+#ifdef CONFIG_UEVENT_HELPER
 	{
 		.procname	= "hotplug",
 		.data		= &uevent_helper,
@@ -651,7 +651,7 @@ static struct ctl_table kern_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dostring,
 	},
-
+#endif
 #ifdef CONFIG_CHR_DEV_SG
 	{
 		.procname	= "sg-big-buff",

lib/kobject_uevent.c

@@ -29,7 +29,9 @@
 
 
 u64 uevent_seqnum;
+#ifdef CONFIG_UEVENT_HELPER
 char uevent_helper[UEVENT_HELPER_PATH_LEN] = CONFIG_UEVENT_HELPER_PATH;
+#endif
 #ifdef CONFIG_NET
 struct uevent_sock {
 	struct list_head list;
@@ -109,6 +111,7 @@ static int kobj_bcast_filter(struct sock *dsk, struct sk_buff *skb, void *data)
 }
 #endif
 
+#ifdef CONFIG_UEVENT_HELPER
 static int kobj_usermode_filter(struct kobject *kobj)
 {
 	const struct kobj_ns_type_operations *ops;
@@ -147,6 +150,7 @@ static void cleanup_uevent_env(struct subprocess_info *info)
 {
 	kfree(info->data);
 }
+#endif
 
 /**
  * kobject_uevent_env - send an uevent with environmental data
@@ -323,6 +327,7 @@ int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
 #endif
 	mutex_unlock(&uevent_sock_mutex);
 
+#ifdef CONFIG_UEVENT_HELPER
 	/* call uevent_helper, usually only enabled during early boot */
 	if (uevent_helper[0] && !kobj_usermode_filter(kobj)) {
 		struct subprocess_info *info;
@@ -347,6 +352,7 @@ int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
 			env = NULL;	/* freed by cleanup_uevent_env */
 		}
 	}
+#endif
 
 exit:
 	kfree(devpath);