sysctl.c 61.7 KB
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/*
 * sysctl.c: General linux system control interface
 *
 * Begun 24 March 1995, Stephen Tweedie
 * Added /proc support, Dec 1995
 * Added bdflush entry and intvec min/max checking, 2/23/96, Tom Dyas.
 * Added hooks for /proc/sys/net (minor, minor patch), 96/4/1, Mike Shaver.
 * Added kernel/java-{interpreter,appletviewer}, 96/5/10, Mike Shaver.
 * Dynamic registration fixes, Stephen Tweedie.
 * Added kswapd-interval, ctrl-alt-del, printk stuff, 1/8/97, Chris Horn.
 * Made sysctl support optional via CONFIG_SYSCTL, 1/10/97, Chris
 *  Horn.
 * Added proc_doulongvec_ms_jiffies_minmax, 09/08/99, Carlos H. Bauer.
 * Added proc_doulongvec_minmax, 09/08/99, Carlos H. Bauer.
 * Changed linked lists to use list.h instead of lists.h, 02/24/00, Bill
 *  Wendling.
 * The list_for_each() macro wasn't appropriate for the sysctl loop.
 *  Removed it and replaced it with older style, 03/23/00, Bill Wendling
 */

#include <linux/module.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/slab.h>
#include <linux/sysctl.h>
#include <linux/proc_fs.h>
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#include <linux/capability.h>
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#include <linux/ctype.h>
#include <linux/utsname.h>
#include <linux/smp_lock.h>
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#include <linux/fs.h>
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#include <linux/init.h>
#include <linux/kernel.h>
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#include <linux/kobject.h>
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#include <linux/net.h>
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#include <linux/sysrq.h>
#include <linux/highuid.h>
#include <linux/writeback.h>
#include <linux/hugetlb.h>
#include <linux/security.h>
#include <linux/initrd.h>
#include <linux/times.h>
#include <linux/limits.h>
#include <linux/dcache.h>
#include <linux/syscalls.h>
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#include <linux/nfs_fs.h>
#include <linux/acpi.h>
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#include <linux/reboot.h>
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#include <asm/uaccess.h>
#include <asm/processor.h>

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#ifdef CONFIG_X86
#include <asm/nmi.h>
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#include <asm/stacktrace.h>
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#endif

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static int deprecated_sysctl_warning(struct __sysctl_args *args);

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#if defined(CONFIG_SYSCTL)

/* External variables not in a header file. */
extern int C_A_D;
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extern int print_fatal_signals;
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extern int sysctl_overcommit_memory;
extern int sysctl_overcommit_ratio;
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extern int sysctl_panic_on_oom;
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extern int sysctl_oom_kill_allocating_task;
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extern int max_threads;
extern int core_uses_pid;
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extern int suid_dumpable;
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extern char core_pattern[];
extern int pid_max;
extern int min_free_kbytes;
extern int printk_ratelimit_jiffies;
extern int printk_ratelimit_burst;
extern int pid_max_min, pid_max_max;
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extern int sysctl_drop_caches;
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extern int percpu_pagelist_fraction;
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extern int compat_log;
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extern int maps_protect;
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extern int sysctl_stat_interval;
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extern int audit_argv_kb;
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/* Constants used for minimum and  maximum */
#ifdef CONFIG_DETECT_SOFTLOCKUP
static int one = 1;
static int sixty = 60;
#endif

#ifdef CONFIG_MMU
static int two = 2;
#endif

static int zero;
static int one_hundred = 100;

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/* this is needed for the proc_dointvec_minmax for [fs_]overflow UID and GID */
static int maxolduid = 65535;
static int minolduid;
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static int min_percpu_pagelist_fract = 8;
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static int ngroups_max = NGROUPS_MAX;

#ifdef CONFIG_KMOD
extern char modprobe_path[];
#endif
#ifdef CONFIG_CHR_DEV_SG
extern int sg_big_buff;
#endif

#ifdef __sparc__
extern char reboot_command [];
extern int stop_a_enabled;
extern int scons_pwroff;
#endif

#ifdef __hppa__
extern int pwrsw_enabled;
extern int unaligned_enabled;
#endif

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#ifdef CONFIG_S390
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#ifdef CONFIG_MATHEMU
extern int sysctl_ieee_emulation_warnings;
#endif
extern int sysctl_userprocess_debug;
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extern int spin_retry;
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#endif

extern int sysctl_hz_timer;

#ifdef CONFIG_BSD_PROCESS_ACCT
extern int acct_parm[];
#endif

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#ifdef CONFIG_IA64
extern int no_unaligned_warning;
#endif

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#ifdef CONFIG_RT_MUTEXES
extern int max_lock_depth;
#endif

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#ifdef CONFIG_SYSCTL_SYSCALL
static int parse_table(int __user *, int, void __user *, size_t __user *,
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		void __user *, size_t, struct ctl_table *);
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#endif

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#ifdef CONFIG_PROC_SYSCTL
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static int proc_do_cad_pid(struct ctl_table *table, int write, struct file *filp,
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		  void __user *buffer, size_t *lenp, loff_t *ppos);
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static int proc_dointvec_taint(struct ctl_table *table, int write, struct file *filp,
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			       void __user *buffer, size_t *lenp, loff_t *ppos);
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#endif
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static struct ctl_table root_table[];
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static struct ctl_table_header root_table_header =
	{ root_table, LIST_HEAD_INIT(root_table_header.ctl_entry) };

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static struct ctl_table kern_table[];
static struct ctl_table vm_table[];
static struct ctl_table fs_table[];
static struct ctl_table debug_table[];
static struct ctl_table dev_table[];
extern struct ctl_table random_table[];
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#ifdef CONFIG_INOTIFY_USER
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extern struct ctl_table inotify_table[];
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#endif
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#ifdef HAVE_ARCH_PICK_MMAP_LAYOUT
int sysctl_legacy_va_layout;
#endif

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extern int prove_locking;
extern int lock_stat;
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/* The default sysctl tables: */

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static struct ctl_table root_table[] = {
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	{
		.ctl_name	= CTL_KERN,
		.procname	= "kernel",
		.mode		= 0555,
		.child		= kern_table,
	},
	{
		.ctl_name	= CTL_VM,
		.procname	= "vm",
		.mode		= 0555,
		.child		= vm_table,
	},
#ifdef CONFIG_NET
	{
		.ctl_name	= CTL_NET,
		.procname	= "net",
		.mode		= 0555,
		.child		= net_table,
	},
#endif
	{
		.ctl_name	= CTL_FS,
		.procname	= "fs",
		.mode		= 0555,
		.child		= fs_table,
	},
	{
		.ctl_name	= CTL_DEBUG,
		.procname	= "debug",
		.mode		= 0555,
		.child		= debug_table,
	},
	{
		.ctl_name	= CTL_DEV,
		.procname	= "dev",
		.mode		= 0555,
		.child		= dev_table,
	},
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/*
 * NOTE: do not add new entries to this table unless you have read
 * Documentation/sysctl/ctl_unnumbered.txt
 */
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	{ .ctl_name = 0 }
};

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#ifdef CONFIG_SCHED_DEBUG
static unsigned long min_sched_granularity_ns = 100000;		/* 100 usecs */
static unsigned long max_sched_granularity_ns = 1000000000;	/* 1 second */
static unsigned long min_wakeup_granularity_ns;			/* 0 usecs */
static unsigned long max_wakeup_granularity_ns = 1000000000;	/* 1 second */
#endif

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static struct ctl_table kern_table[] = {
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#ifdef CONFIG_SCHED_DEBUG
	{
		.ctl_name	= CTL_UNNUMBERED,
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		.procname	= "sched_nr_latency",
		.data		= &sysctl_sched_nr_latency,
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		.maxlen		= sizeof(unsigned int),
		.mode		= 0644,
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		.proc_handler	= &proc_dointvec,
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	},
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	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "sched_latency_ns",
		.data		= &sysctl_sched_latency,
		.maxlen		= sizeof(unsigned int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec_minmax,
		.strategy	= &sysctl_intvec,
		.extra1		= &min_sched_granularity_ns,
		.extra2		= &max_sched_granularity_ns,
	},
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	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "sched_wakeup_granularity_ns",
		.data		= &sysctl_sched_wakeup_granularity,
		.maxlen		= sizeof(unsigned int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec_minmax,
		.strategy	= &sysctl_intvec,
		.extra1		= &min_wakeup_granularity_ns,
		.extra2		= &max_wakeup_granularity_ns,
	},
	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "sched_batch_wakeup_granularity_ns",
		.data		= &sysctl_sched_batch_wakeup_granularity,
		.maxlen		= sizeof(unsigned int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec_minmax,
		.strategy	= &sysctl_intvec,
		.extra1		= &min_wakeup_granularity_ns,
		.extra2		= &max_wakeup_granularity_ns,
	},
	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "sched_child_runs_first",
		.data		= &sysctl_sched_child_runs_first,
		.maxlen		= sizeof(unsigned int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "sched_features",
		.data		= &sysctl_sched_features,
		.maxlen		= sizeof(unsigned int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "sched_migration_cost",
		.data		= &sysctl_sched_migration_cost,
		.maxlen		= sizeof(unsigned int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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#endif
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	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "sched_compat_yield",
		.data		= &sysctl_sched_compat_yield,
		.maxlen		= sizeof(unsigned int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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#ifdef CONFIG_PROVE_LOCKING
	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "prove_locking",
		.data		= &prove_locking,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
#endif
#ifdef CONFIG_LOCK_STAT
	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "lock_stat",
		.data		= &lock_stat,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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#endif
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	{
		.ctl_name	= KERN_PANIC,
		.procname	= "panic",
		.data		= &panic_timeout,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
	{
		.ctl_name	= KERN_CORE_USES_PID,
		.procname	= "core_uses_pid",
		.data		= &core_uses_pid,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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#ifdef CONFIG_AUDITSYSCALL
	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "audit_argv_kb",
		.data		= &audit_argv_kb,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
#endif
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	{
		.ctl_name	= KERN_CORE_PATTERN,
		.procname	= "core_pattern",
		.data		= core_pattern,
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		.maxlen		= CORENAME_MAX_SIZE,
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		.mode		= 0644,
		.proc_handler	= &proc_dostring,
		.strategy	= &sysctl_string,
	},
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#ifdef CONFIG_PROC_SYSCTL
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	{
		.procname	= "tainted",
		.data		= &tainted,
		.maxlen		= sizeof(int),
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		.mode		= 0644,
		.proc_handler	= &proc_dointvec_taint,
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	},
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#endif
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	{
		.procname	= "cap-bound",
		.data		= &cap_bset,
		.maxlen		= sizeof(kernel_cap_t),
		.mode		= 0600,
		.proc_handler	= &proc_dointvec_bset,
	},
#ifdef CONFIG_BLK_DEV_INITRD
	{
		.ctl_name	= KERN_REALROOTDEV,
		.procname	= "real-root-dev",
		.data		= &real_root_dev,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
#endif
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	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "print-fatal-signals",
		.data		= &print_fatal_signals,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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#ifdef __sparc__
	{
		.ctl_name	= KERN_SPARC_REBOOT,
		.procname	= "reboot-cmd",
		.data		= reboot_command,
		.maxlen		= 256,
		.mode		= 0644,
		.proc_handler	= &proc_dostring,
		.strategy	= &sysctl_string,
	},
	{
		.ctl_name	= KERN_SPARC_STOP_A,
		.procname	= "stop-a",
		.data		= &stop_a_enabled,
		.maxlen		= sizeof (int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
	{
		.ctl_name	= KERN_SPARC_SCONS_PWROFF,
		.procname	= "scons-poweroff",
		.data		= &scons_pwroff,
		.maxlen		= sizeof (int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
#endif
#ifdef __hppa__
	{
		.ctl_name	= KERN_HPPA_PWRSW,
		.procname	= "soft-power",
		.data		= &pwrsw_enabled,
		.maxlen		= sizeof (int),
	 	.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
	{
		.ctl_name	= KERN_HPPA_UNALIGNED,
		.procname	= "unaligned-trap",
		.data		= &unaligned_enabled,
		.maxlen		= sizeof (int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
#endif
	{
		.ctl_name	= KERN_CTLALTDEL,
		.procname	= "ctrl-alt-del",
		.data		= &C_A_D,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
	{
		.ctl_name	= KERN_PRINTK,
		.procname	= "printk",
		.data		= &console_loglevel,
		.maxlen		= 4*sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
#ifdef CONFIG_KMOD
	{
		.ctl_name	= KERN_MODPROBE,
		.procname	= "modprobe",
		.data		= &modprobe_path,
		.maxlen		= KMOD_PATH_LEN,
		.mode		= 0644,
		.proc_handler	= &proc_dostring,
		.strategy	= &sysctl_string,
	},
#endif
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#if defined(CONFIG_HOTPLUG) && defined(CONFIG_NET)
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	{
		.ctl_name	= KERN_HOTPLUG,
		.procname	= "hotplug",
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		.data		= &uevent_helper,
		.maxlen		= UEVENT_HELPER_PATH_LEN,
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		.mode		= 0644,
		.proc_handler	= &proc_dostring,
		.strategy	= &sysctl_string,
	},
#endif
#ifdef CONFIG_CHR_DEV_SG
	{
		.ctl_name	= KERN_SG_BIG_BUFF,
		.procname	= "sg-big-buff",
		.data		= &sg_big_buff,
		.maxlen		= sizeof (int),
		.mode		= 0444,
		.proc_handler	= &proc_dointvec,
	},
#endif
#ifdef CONFIG_BSD_PROCESS_ACCT
	{
		.ctl_name	= KERN_ACCT,
		.procname	= "acct",
		.data		= &acct_parm,
		.maxlen		= 3*sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
#endif
#ifdef CONFIG_MAGIC_SYSRQ
	{
		.ctl_name	= KERN_SYSRQ,
		.procname	= "sysrq",
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		.data		= &__sysrq_enabled,
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		.maxlen		= sizeof (int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
#endif
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#ifdef CONFIG_PROC_SYSCTL
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	{
		.procname	= "cad_pid",
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		.data		= NULL,
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		.maxlen		= sizeof (int),
		.mode		= 0600,
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		.proc_handler	= &proc_do_cad_pid,
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	},
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#endif
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	{
		.ctl_name	= KERN_MAX_THREADS,
		.procname	= "threads-max",
		.data		= &max_threads,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
	{
		.ctl_name	= KERN_RANDOM,
		.procname	= "random",
		.mode		= 0555,
		.child		= random_table,
	},
	{
		.ctl_name	= KERN_OVERFLOWUID,
		.procname	= "overflowuid",
		.data		= &overflowuid,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec_minmax,
		.strategy	= &sysctl_intvec,
		.extra1		= &minolduid,
		.extra2		= &maxolduid,
	},
	{
		.ctl_name	= KERN_OVERFLOWGID,
		.procname	= "overflowgid",
		.data		= &overflowgid,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec_minmax,
		.strategy	= &sysctl_intvec,
		.extra1		= &minolduid,
		.extra2		= &maxolduid,
	},
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#ifdef CONFIG_S390
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#ifdef CONFIG_MATHEMU
	{
		.ctl_name	= KERN_IEEE_EMULATION_WARNINGS,
		.procname	= "ieee_emulation_warnings",
		.data		= &sysctl_ieee_emulation_warnings,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
#endif
#ifdef CONFIG_NO_IDLE_HZ
	{
		.ctl_name       = KERN_HZ_TIMER,
		.procname       = "hz_timer",
		.data           = &sysctl_hz_timer,
		.maxlen         = sizeof(int),
		.mode           = 0644,
		.proc_handler   = &proc_dointvec,
	},
#endif
	{
		.ctl_name	= KERN_S390_USER_DEBUG_LOGGING,
		.procname	= "userprocess_debug",
		.data		= &sysctl_userprocess_debug,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
#endif
	{
		.ctl_name	= KERN_PIDMAX,
		.procname	= "pid_max",
		.data		= &pid_max,
		.maxlen		= sizeof (int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec_minmax,
		.strategy	= sysctl_intvec,
		.extra1		= &pid_max_min,
		.extra2		= &pid_max_max,
	},
	{
		.ctl_name	= KERN_PANIC_ON_OOPS,
		.procname	= "panic_on_oops",
		.data		= &panic_on_oops,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
	{
		.ctl_name	= KERN_PRINTK_RATELIMIT,
		.procname	= "printk_ratelimit",
		.data		= &printk_ratelimit_jiffies,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec_jiffies,
		.strategy	= &sysctl_jiffies,
	},
	{
		.ctl_name	= KERN_PRINTK_RATELIMIT_BURST,
		.procname	= "printk_ratelimit_burst",
		.data		= &printk_ratelimit_burst,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
	{
		.ctl_name	= KERN_NGROUPS_MAX,
		.procname	= "ngroups_max",
		.data		= &ngroups_max,
		.maxlen		= sizeof (int),
		.mode		= 0444,
		.proc_handler	= &proc_dointvec,
	},
#if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86)
	{
		.ctl_name       = KERN_UNKNOWN_NMI_PANIC,
		.procname       = "unknown_nmi_panic",
		.data           = &unknown_nmi_panic,
		.maxlen         = sizeof (int),
		.mode           = 0644,
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		.proc_handler   = &proc_dointvec,
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	},
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	{
		.procname       = "nmi_watchdog",
		.data           = &nmi_watchdog_enabled,
		.maxlen         = sizeof (int),
		.mode           = 0644,
		.proc_handler   = &proc_nmi_enabled,
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	},
#endif
#if defined(CONFIG_X86)
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	{
		.ctl_name	= KERN_PANIC_ON_NMI,
		.procname	= "panic_on_unrecovered_nmi",
		.data		= &panic_on_unrecovered_nmi,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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	{
		.ctl_name	= KERN_BOOTLOADER_TYPE,
		.procname	= "bootloader_type",
		.data		= &bootloader_type,
		.maxlen		= sizeof (int),
		.mode		= 0444,
		.proc_handler	= &proc_dointvec,
	},
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	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "kstack_depth_to_print",
		.data		= &kstack_depth_to_print,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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#endif
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#if defined(CONFIG_MMU)
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	{
		.ctl_name	= KERN_RANDOMIZE,
		.procname	= "randomize_va_space",
		.data		= &randomize_va_space,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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#endif
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#if defined(CONFIG_S390) && defined(CONFIG_SMP)
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	{
		.ctl_name	= KERN_SPIN_RETRY,
		.procname	= "spin_retry",
		.data		= &spin_retry,
		.maxlen		= sizeof (int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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#endif
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#if	defined(CONFIG_ACPI_SLEEP) && defined(CONFIG_X86)
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	{
		.procname	= "acpi_video_flags",
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		.data		= &acpi_realmode_flags,
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		.maxlen		= sizeof (unsigned long),
		.mode		= 0644,
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		.proc_handler	= &proc_doulongvec_minmax,
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	},
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#endif
#ifdef CONFIG_IA64
	{
		.ctl_name	= KERN_IA64_UNALIGNED,
		.procname	= "ignore-unaligned-usertrap",
		.data		= &no_unaligned_warning,
		.maxlen		= sizeof (int),
	 	.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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#endif
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#ifdef CONFIG_DETECT_SOFTLOCKUP
	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "softlockup_thresh",
		.data		= &softlockup_thresh,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec_minmax,
		.strategy	= &sysctl_intvec,
		.extra1		= &one,
		.extra2		= &sixty,
	},
#endif
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#ifdef CONFIG_COMPAT
	{
		.ctl_name	= KERN_COMPAT_LOG,
		.procname	= "compat-log",
		.data		= &compat_log,
		.maxlen		= sizeof (int),
	 	.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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#endif
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#ifdef CONFIG_RT_MUTEXES
	{
		.ctl_name	= KERN_MAX_LOCK_DEPTH,
		.procname	= "max_lock_depth",
		.data		= &max_lock_depth,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
#endif
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#ifdef CONFIG_PROC_FS
	{
		.ctl_name       = CTL_UNNUMBERED,
		.procname       = "maps_protect",
		.data           = &maps_protect,
		.maxlen         = sizeof(int),
		.mode           = 0644,
		.proc_handler   = &proc_dointvec,
	},
#endif
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	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "poweroff_cmd",
		.data		= &poweroff_cmd,
		.maxlen		= POWEROFF_CMD_PATH_LEN,
		.mode		= 0644,
		.proc_handler	= &proc_dostring,
		.strategy	= &sysctl_string,
	},
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/*
 * NOTE: do not add new entries to this table unless you have read
 * Documentation/sysctl/ctl_unnumbered.txt
 */
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	{ .ctl_name = 0 }
};

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static struct ctl_table vm_table[] = {
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	{
		.ctl_name	= VM_OVERCOMMIT_MEMORY,
		.procname	= "overcommit_memory",
		.data		= &sysctl_overcommit_memory,
		.maxlen		= sizeof(sysctl_overcommit_memory),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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	{
		.ctl_name	= VM_PANIC_ON_OOM,
		.procname	= "panic_on_oom",
		.data		= &sysctl_panic_on_oom,
		.maxlen		= sizeof(sysctl_panic_on_oom),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "oom_kill_allocating_task",
		.data		= &sysctl_oom_kill_allocating_task,
		.maxlen		= sizeof(sysctl_oom_kill_allocating_task),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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	{
		.ctl_name	= VM_OVERCOMMIT_RATIO,
		.procname	= "overcommit_ratio",
		.data		= &sysctl_overcommit_ratio,
		.maxlen		= sizeof(sysctl_overcommit_ratio),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
	{
		.ctl_name	= VM_PAGE_CLUSTER,
		.procname	= "page-cluster", 
		.data		= &page_cluster,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
	{
		.ctl_name	= VM_DIRTY_BACKGROUND,
		.procname	= "dirty_background_ratio",
		.data		= &dirty_background_ratio,
		.maxlen		= sizeof(dirty_background_ratio),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec_minmax,
		.strategy	= &sysctl_intvec,
		.extra1		= &zero,
		.extra2		= &one_hundred,
	},
	{
		.ctl_name	= VM_DIRTY_RATIO,
		.procname	= "dirty_ratio",
		.data		= &vm_dirty_ratio,
		.maxlen		= sizeof(vm_dirty_ratio),
		.mode		= 0644,
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		.proc_handler	= &dirty_ratio_handler,
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		.strategy	= &sysctl_intvec,
		.extra1		= &zero,
		.extra2		= &one_hundred,
	},
	{
		.procname	= "dirty_writeback_centisecs",
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		.data		= &dirty_writeback_interval,
		.maxlen		= sizeof(dirty_writeback_interval),
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		.mode		= 0644,
		.proc_handler	= &dirty_writeback_centisecs_handler,
	},
	{
		.procname	= "dirty_expire_centisecs",
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		.data		= &dirty_expire_interval,
		.maxlen		= sizeof(dirty_expire_interval),
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		.mode		= 0644,
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		.proc_handler	= &proc_dointvec_userhz_jiffies,
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	},
	{
		.ctl_name	= VM_NR_PDFLUSH_THREADS,
		.procname	= "nr_pdflush_threads",
		.data		= &nr_pdflush_threads,
		.maxlen		= sizeof nr_pdflush_threads,
		.mode		= 0444 /* read-only*/,
		.proc_handler	= &proc_dointvec,
	},
	{
		.ctl_name	= VM_SWAPPINESS,
		.procname	= "swappiness",
		.data		= &vm_swappiness,
		.maxlen		= sizeof(vm_swappiness),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec_minmax,
		.strategy	= &sysctl_intvec,
		.extra1		= &zero,
		.extra2		= &one_hundred,
	},
#ifdef CONFIG_HUGETLB_PAGE
	 {
		.procname	= "nr_hugepages",
		.data		= &max_huge_pages,
		.maxlen		= sizeof(unsigned long),
		.mode		= 0644,
		.proc_handler	= &hugetlb_sysctl_handler,
		.extra1		= (void *)&hugetlb_zero,
		.extra2		= (void *)&hugetlb_infinity,
	 },
	 {
		.ctl_name	= VM_HUGETLB_GROUP,
		.procname	= "hugetlb_shm_group",
		.data		= &sysctl_hugetlb_shm_group,
		.maxlen		= sizeof(gid_t),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	 },
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	 {
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "hugepages_treat_as_movable",
		.data		= &hugepages_treat_as_movable,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &hugetlb_treat_movable_handler,
	},
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	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "hugetlb_dynamic_pool",
		.data		= &hugetlb_dynamic_pool,
		.maxlen		= sizeof(hugetlb_dynamic_pool),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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#endif
	{
		.ctl_name	= VM_LOWMEM_RESERVE_RATIO,
		.procname	= "lowmem_reserve_ratio",
		.data		= &sysctl_lowmem_reserve_ratio,
		.maxlen		= sizeof(sysctl_lowmem_reserve_ratio),
		.mode		= 0644,
		.proc_handler	= &lowmem_reserve_ratio_sysctl_handler,
		.strategy	= &sysctl_intvec,
	},
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	{
		.ctl_name	= VM_DROP_PAGECACHE,
		.procname	= "drop_caches",
		.data		= &sysctl_drop_caches,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= drop_caches_sysctl_handler,
		.strategy	= &sysctl_intvec,
	},
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	{
		.ctl_name	= VM_MIN_FREE_KBYTES,
		.procname	= "min_free_kbytes",
		.data		= &min_free_kbytes,
		.maxlen		= sizeof(min_free_kbytes),
		.mode		= 0644,
		.proc_handler	= &min_free_kbytes_sysctl_handler,
		.strategy	= &sysctl_intvec,
		.extra1		= &zero,
	},
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	{
		.ctl_name	= VM_PERCPU_PAGELIST_FRACTION,
		.procname	= "percpu_pagelist_fraction",
		.data		= &percpu_pagelist_fraction,
		.maxlen		= sizeof(percpu_pagelist_fraction),
		.mode		= 0644,
		.proc_handler	= &percpu_pagelist_fraction_sysctl_handler,
		.strategy	= &sysctl_intvec,
		.extra1		= &min_percpu_pagelist_fract,
	},
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#ifdef CONFIG_MMU
	{
		.ctl_name	= VM_MAX_MAP_COUNT,
		.procname	= "max_map_count",
		.data		= &sysctl_max_map_count,
		.maxlen		= sizeof(sysctl_max_map_count),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec
	},
#endif
	{
		.ctl_name	= VM_LAPTOP_MODE,
		.procname	= "laptop_mode",
		.data		= &laptop_mode,
		.maxlen		= sizeof(laptop_mode),
		.mode		= 0644,
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		.proc_handler	= &proc_dointvec_jiffies,
		.strategy	= &sysctl_jiffies,
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	},
	{
		.ctl_name	= VM_BLOCK_DUMP,
		.procname	= "block_dump",
		.data		= &block_dump,
		.maxlen		= sizeof(block_dump),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
		.strategy	= &sysctl_intvec,
		.extra1		= &zero,
	},
	{
		.ctl_name	= VM_VFS_CACHE_PRESSURE,
		.procname	= "vfs_cache_pressure",
		.data		= &sysctl_vfs_cache_pressure,
		.maxlen		= sizeof(sysctl_vfs_cache_pressure),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
		.strategy	= &sysctl_intvec,
		.extra1		= &zero,
	},
#ifdef HAVE_ARCH_PICK_MMAP_LAYOUT
	{
		.ctl_name	= VM_LEGACY_VA_LAYOUT,
		.procname	= "legacy_va_layout",
		.data		= &sysctl_legacy_va_layout,
		.maxlen		= sizeof(sysctl_legacy_va_layout),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
		.strategy	= &sysctl_intvec,
		.extra1		= &zero,
	},
#endif
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#ifdef CONFIG_NUMA
	{
		.ctl_name	= VM_ZONE_RECLAIM_MODE,
		.procname	= "zone_reclaim_mode",
		.data		= &zone_reclaim_mode,
		.maxlen		= sizeof(zone_reclaim_mode),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
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		.strategy	= &sysctl_intvec,
		.extra1		= &zero,
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	},
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	{
		.ctl_name	= VM_MIN_UNMAPPED,
		.procname	= "min_unmapped_ratio",
		.data		= &sysctl_min_unmapped_ratio,
		.maxlen		= sizeof(sysctl_min_unmapped_ratio),
		.mode		= 0644,
		.proc_handler	= &sysctl_min_unmapped_ratio_sysctl_handler,
		.strategy	= &sysctl_intvec,
		.extra1		= &zero,
		.extra2		= &one_hundred,
	},
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	{
		.ctl_name	= VM_MIN_SLAB,
		.procname	= "min_slab_ratio",
		.data		= &sysctl_min_slab_ratio,
		.maxlen		= sizeof(sysctl_min_slab_ratio),
		.mode		= 0644,
		.proc_handler	= &sysctl_min_slab_ratio_sysctl_handler,
		.strategy	= &sysctl_intvec,
		.extra1		= &zero,
		.extra2		= &one_hundred,
	},
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#endif
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#ifdef CONFIG_SMP
	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "stat_interval",
		.data		= &sysctl_stat_interval,
		.maxlen		= sizeof(sysctl_stat_interval),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec_jiffies,
		.strategy	= &sysctl_jiffies,
	},
#endif
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#ifdef CONFIG_SECURITY
	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "mmap_min_addr",
		.data		= &mmap_min_addr,
		.maxlen         = sizeof(unsigned long),
		.mode		= 0644,
		.proc_handler	= &proc_doulongvec_minmax,
	},
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#endif
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#ifdef CONFIG_NUMA
	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "numa_zonelist_order",
		.data		= &numa_zonelist_order,
		.maxlen		= NUMA_ZONELIST_ORDER_LEN,
		.mode		= 0644,
		.proc_handler	= &numa_zonelist_order_handler,
		.strategy	= &sysctl_string,
	},
#endif
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#if (defined(CONFIG_X86_32) && !defined(CONFIG_UML))|| \
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   (defined(CONFIG_SUPERH) && defined(CONFIG_VSYSCALL))
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	{
		.ctl_name	= VM_VDSO_ENABLED,
		.procname	= "vdso_enabled",
		.data		= &vdso_enabled,
		.maxlen		= sizeof(vdso_enabled),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
		.strategy	= &sysctl_intvec,
		.extra1		= &zero,
	},
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#endif
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/*
 * NOTE: do not add new entries to this table unless you have read
 * Documentation/sysctl/ctl_unnumbered.txt
 */
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	{ .ctl_name = 0 }
};

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#if defined(CONFIG_BINFMT_MISC) || defined(CONFIG_BINFMT_MISC_MODULE)
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static struct ctl_table binfmt_misc_table[] = {
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	{ .ctl_name = 0 }
};
#endif

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static struct ctl_table fs_table[] = {
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	{
		.ctl_name	= FS_NRINODE,
		.procname	= "inode-nr",
		.data		= &inodes_stat,
		.maxlen		= 2*sizeof(int),
		.mode		= 0444,
		.proc_handler	= &proc_dointvec,
	},
	{
		.ctl_name	= FS_STATINODE,
		.procname	= "inode-state",
		.data		= &inodes_stat,
		.maxlen		= 7*sizeof(int),
		.mode		= 0444,
		.proc_handler	= &proc_dointvec,
	},
	{
		.procname	= "file-nr",
		.data		= &files_stat,
		.maxlen		= 3*sizeof(int),
		.mode		= 0444,
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		.proc_handler	= &proc_nr_files,
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	},
	{
		.ctl_name	= FS_MAXFILE,
		.procname	= "file-max",
		.data		= &files_stat.max_files,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
	{
		.ctl_name	= FS_DENTRY,
		.procname	= "dentry-state",
		.data		= &dentry_stat,
		.maxlen		= 6*sizeof(int),
		.mode		= 0444,
		.proc_handler	= &proc_dointvec,
	},
	{
		.ctl_name	= FS_OVERFLOWUID,
		.procname	= "overflowuid",
		.data		= &fs_overflowuid,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec_minmax,
		.strategy	= &sysctl_intvec,
		.extra1		= &minolduid,
		.extra2		= &maxolduid,
	},
	{
		.ctl_name	= FS_OVERFLOWGID,
		.procname	= "overflowgid",
		.data		= &fs_overflowgid,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec_minmax,
		.strategy	= &sysctl_intvec,
		.extra1		= &minolduid,
		.extra2		= &maxolduid,
	},
	{
		.ctl_name	= FS_LEASES,
		.procname	= "leases-enable",
		.data		= &leases_enable,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
#ifdef CONFIG_DNOTIFY
	{
		.ctl_name	= FS_DIR_NOTIFY,
		.procname	= "dir-notify-enable",
		.data		= &dir_notify_enable,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
#endif
#ifdef CONFIG_MMU
	{
		.ctl_name	= FS_LEASE_TIME,
		.procname	= "lease-break-time",
		.data		= &lease_break_time,
		.maxlen		= sizeof(int),
		.mode		= 0644,
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		.proc_handler	= &proc_dointvec_minmax,
		.strategy	= &sysctl_intvec,
		.extra1		= &zero,
		.extra2		= &two,
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	},
	{
		.procname	= "aio-nr",
		.data		= &aio_nr,
		.maxlen		= sizeof(aio_nr),
		.mode		= 0444,
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		.proc_handler	= &proc_doulongvec_minmax,
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	},
	{
		.procname	= "aio-max-nr",
		.data		= &aio_max_nr,
		.maxlen		= sizeof(aio_max_nr),
		.mode		= 0644,
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		.proc_handler	= &proc_doulongvec_minmax,
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	},
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#ifdef CONFIG_INOTIFY_USER
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	{
		.ctl_name	= FS_INOTIFY,
		.procname	= "inotify",
		.mode		= 0555,
		.child		= inotify_table,
	},
#endif	
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#endif
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	{
		.ctl_name	= KERN_SETUID_DUMPABLE,
		.procname	= "suid_dumpable",
		.data		= &suid_dumpable,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
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#if defined(CONFIG_BINFMT_MISC) || defined(CONFIG_BINFMT_MISC_MODULE)
	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "binfmt_misc",
		.mode		= 0555,
		.child		= binfmt_misc_table,
	},
#endif
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/*
 * NOTE: do not add new entries to this table unless you have read
 * Documentation/sysctl/ctl_unnumbered.txt
 */
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	{ .ctl_name = 0 }
};

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static struct ctl_table debug_table[] = {
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#if defined(CONFIG_X86) || defined(CONFIG_PPC)
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	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "exception-trace",
		.data		= &show_unhandled_signals,
		.maxlen		= sizeof(int),
		.mode		= 0644,
		.proc_handler	= proc_dointvec
	},
#endif
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	{ .ctl_name = 0 }
};

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static struct ctl_table dev_table[] = {
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	{ .ctl_name = 0 }
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};
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static DEFINE_SPINLOCK(sysctl_lock);

/* called under sysctl_lock */
static int use_table(struct ctl_table_header *p)
{
	if (unlikely(p->unregistering))
		return 0;
	p->used++;
	return 1;
}

/* called under sysctl_lock */
static void unuse_table(struct ctl_table_header *p)
{
	if (!--p->used)
		if (unlikely(p->unregistering))
			complete(p->unregistering);
}

/* called under sysctl_lock, will reacquire if has to wait */
static void start_unregistering(struct ctl_table_header *p)
{
	/*
	 * if p->used is 0, nobody will ever touch that entry again;
	 * we'll eliminate all paths to it before dropping sysctl_lock
	 */
	if (unlikely(p->used)) {
		struct completion wait;
		init_completion(&wait);
		p->unregistering = &wait;
		spin_unlock(&sysctl_lock);
		wait_for_completion(&wait);
		spin_lock(&sysctl_lock);
	}
	/*
	 * do not remove from the list until nobody holds it; walking the
	 * list in do_sysctl() relies on that.
	 */
	list_del_init(&p->ctl_entry);
}

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void sysctl_head_finish(struct ctl_table_header *head)
{
	if (!head)
		return;
	spin_lock(&sysctl_lock);
	unuse_table(head);
	spin_unlock(&sysctl_lock);
}

struct ctl_table_header *sysctl_head_next(struct ctl_table_header *prev)
{
	struct ctl_table_header *head;
	struct list_head *tmp;
	spin_lock(&sysctl_lock);
	if (prev) {
		tmp = &prev->ctl_entry;
		unuse_table(prev);
		goto next;
	}
	tmp = &root_table_header.ctl_entry;
	for (;;) {
		head = list_entry(tmp, struct ctl_table_header, ctl_entry);

		if (!use_table(head))
			goto next;
		spin_unlock(&sysctl_lock);
		return head;
	next:
		tmp = tmp->next;
		if (tmp == &root_table_header.ctl_entry)
			break;
	}
	spin_unlock(&sysctl_lock);
	return NULL;
}

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#ifdef CONFIG_SYSCTL_SYSCALL
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int do_sysctl(int __user *name, int nlen, void __user *oldval, size_t __user *oldlenp,
	       void __user *newval, size_t newlen)
{
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	struct ctl_table_header *head;
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	int error = -ENOTDIR;
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	if (nlen <= 0 || nlen >= CTL_MAXNAME)
		return -ENOTDIR;
	if (oldval) {
		int old_len;
		if (!oldlenp || get_user(old_len, oldlenp))
			return -EFAULT;
	}
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	for (head = sysctl_head_next(NULL); head;
			head = sysctl_head_next(head)) {
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		error = parse_table(name, nlen, oldval, oldlenp, 
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					newval, newlen, head->ctl_table);
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		if (error != -ENOTDIR) {
			sysctl_head_finish(head);
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			break;
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		}
	}
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	return error;
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}

asmlinkage long sys_sysctl(struct __sysctl_args __user *args)
{
	struct __sysctl_args tmp;
	int error;

	if (copy_from_user(&tmp, args, sizeof(tmp)))
		return -EFAULT;

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	error = deprecated_sysctl_warning(&tmp);
	if (error)
		goto out;

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	lock_kernel();
	error = do_sysctl(tmp.name, tmp.nlen, tmp.oldval, tmp.oldlenp,
			  tmp.newval, tmp.newlen);
	unlock_kernel();
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out:
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	return error;
}
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#endif /* CONFIG_SYSCTL_SYSCALL */
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/*
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 * sysctl_perm does NOT grant the superuser all rights automatically, because
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 * some sysctl variables are readonly even to root.
 */

static int test_perm(int mode, int op)
{
	if (!current->euid)
		mode >>= 6;
	else if (in_egroup_p(0))
		mode >>= 3;
	if ((mode & op & 0007) == op)
		return 0;
	return -EACCES;
}

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int sysctl_perm(struct ctl_table *table, int op)
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{
	int error;
	error = security_sysctl(table, op);
	if (error)
		return error;
	return test_perm(table->mode, op);
}

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#ifdef CONFIG_SYSCTL_SYSCALL
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static int parse_table(int __user *name, int nlen,
		       void __user *oldval, size_t __user *oldlenp,
		       void __user *newval, size_t newlen,
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		       struct ctl_table *table)
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{
	int n;
repeat:
	if (!nlen)
		return -ENOTDIR;
	if (get_user(n, name))
		return -EFAULT;
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	for ( ; table->ctl_name || table->procname; table++) {
		if (!table->ctl_name)
			continue;
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		if (n == table->ctl_name) {
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			int error;
			if (table->child) {
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				if (sysctl_perm(table, 001))
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					return -EPERM;
				name++;
				nlen--;
				table = table->child;
				goto repeat;
			}
			error = do_sysctl_strategy(table, name, nlen,
						   oldval, oldlenp,
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						   newval, newlen);
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			return error;
		}
	}
	return -ENOTDIR;
}

/* Perform the actual read/write of a sysctl table entry. */
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int do_sysctl_strategy (struct ctl_table *table,
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			int __user *name, int nlen,
			void __user *oldval, size_t __user *oldlenp,
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			void __user *newval, size_t newlen)
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{
	int op = 0, rc;

	if (oldval)
		op |= 004;
	if (newval) 
		op |= 002;
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	if (sysctl_perm(table, op))
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		return -EPERM;

	if (table->strategy) {
		rc = table->strategy(table, name, nlen, oldval, oldlenp,
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				     newval, newlen);
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		if (rc < 0)
			return rc;
		if (rc > 0)
			return 0;
	}

	/* If there is no strategy routine, or if the strategy returns
	 * zero, proceed with automatic r/w */
	if (table->data && table->maxlen) {
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		rc = sysctl_data(table, name, nlen, oldval, oldlenp,
				 newval, newlen);
		if (rc < 0)
			return rc;
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	}
	return 0;
}
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#endif /* CONFIG_SYSCTL_SYSCALL */
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static void sysctl_set_parent(struct ctl_table *parent, struct ctl_table *table)
{
	for (; table->ctl_name || table->procname; table++) {
		table->parent = parent;
		if (table->child)
			sysctl_set_parent(table, table->child);
	}
}

static __init int sysctl_init(void)
{
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	int err;
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	sysctl_set_parent(NULL, root_table);
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	err = sysctl_check_table(root_table);
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	return 0;
}

core_initcall(sysctl_init);

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/**
 * register_sysctl_table - register a sysctl hierarchy
 * @table: the top-level table structure
 *
 * Register a sysctl table hierarchy. @table should be a filled in ctl_table
 * array. An entry with a ctl_name of 0 terminates the table. 
 *
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 * The members of the &struct ctl_table structure are used as follows:
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 *
 * ctl_name - This is the numeric sysctl value used by sysctl(2). The number
 *            must be unique within that level of sysctl
 *
 * procname - the name of the sysctl file under /proc/sys. Set to %NULL to not
 *            enter a sysctl file
 *
 * data - a pointer to data for use by proc_handler
 *
 * maxlen - the maximum size in bytes of the data
 *
 * mode - the file permissions for the /proc/sys file, and for sysctl(2)
 *
 * child - a pointer to the child sysctl table if this entry is a directory, or
 *         %NULL.
 *
 * proc_handler - the text handler routine (described below)
 *
 * strategy - the strategy routine (described below)
 *
 * de - for internal use by the sysctl routines
 *
 * extra1, extra2 - extra pointers usable by the proc handler routines
 *
 * Leaf nodes in the sysctl tree will be represented by a single file
 * under /proc; non-leaf nodes will be represented by directories.
 *
 * sysctl(2) can automatically manage read and write requests through
 * the sysctl table.  The data and maxlen fields of the ctl_table
 * struct enable minimal validation of the values being written to be
 * performed, and the mode field allows minimal authentication.
 *
 * More sophisticated management can be enabled by the provision of a
 * strategy routine with the table entry.  This will be called before
 * any automatic read or write of the data is performed.
 *
 * The strategy routine may return
 *
 * < 0 - Error occurred (error is passed to user process)
 *
 * 0   - OK - proceed with automatic read or write.
 *
 * > 0 - OK - read or write has been done by the strategy routine, so
 *       return immediately.
 *
 * There must be a proc_handler routine for any terminal nodes
 * mirrored under /proc/sys (non-terminals are handled by a built-in
 * directory handler).  Several default handlers are available to
 * cover common cases -
 *
 * proc_dostring(), proc_dointvec(), proc_dointvec_jiffies(),
 * proc_dointvec_userhz_jiffies(), proc_dointvec_minmax(), 
 * proc_doulongvec_ms_jiffies_minmax(), proc_doulongvec_minmax()
 *
 * It is the handler's job to read the input buffer from user memory
 * and process it. The handler should return 0 on success.
 *
 * This routine returns %NULL on a failure to register, and a pointer
 * to the table header on success.
 */