text: /* SPDX-License-Identifier: GPL-2.0 */
  /*
   * sysctl.h: General linux system control interface
   *
   * Begun 24 March 1995, Stephen Tweedie
   *
   ****************************************************************
   ****************************************************************
   **
   **  WARNING:
   **  The values in this file are exported to user space via 
   **  the sysctl() binary interface.  Do *NOT* change the
   **  numbering of any existing values here, and do not change
   **  any numbers within any one set of values.  If you have to
   **  redefine an existing interface, use a new number for it.
   **  The kernel will then return -ENOTDIR to any application using
   **  the old binary interface.
   **
   ****************************************************************
   ****************************************************************
   */
  #ifndef _LINUX_SYSCTL_H
  #define _LINUX_SYSCTL_H
  
  #include <linux/list.h>
  #include <linux/rcupdate.h>
  #include <linux/wait.h>
  #include <linux/rbtree.h>
  #include <linux/uidgid.h>
  #include <uapi/linux/sysctl.h>
  
  /* For the /proc/sys support */
  struct completion;
  struct ctl_table;
  struct nsproxy;
  struct ctl_table_root;
  struct ctl_table_header;
  struct ctl_dir;
  
  typedef int proc_handler (struct ctl_table *ctl, int write,
  			  void __user *buffer, size_t *lenp, loff_t *ppos);
  
  extern int proc_dostring(struct ctl_table *, int,
  			 void __user *, size_t *, loff_t *);
  extern int proc_dointvec(struct ctl_table *, int,
  			 void __user *, size_t *, loff_t *);
  extern int proc_douintvec(struct ctl_table *, int,
  			 void __user *, size_t *, loff_t *);
  extern int proc_dointvec_minmax(struct ctl_table *, int,
  				void __user *, size_t *, loff_t *);
  extern int proc_douintvec_minmax(struct ctl_table *table, int write,
  				 void __user *buffer, size_t *lenp,
  				 loff_t *ppos);
  extern int proc_dointvec_jiffies(struct ctl_table *, int,
  				 void __user *, size_t *, loff_t *);
  extern int proc_dointvec_userhz_jiffies(struct ctl_table *, int,
  					void __user *, size_t *, loff_t *);
  extern int proc_dointvec_ms_jiffies(struct ctl_table *, int,
  				    void __user *, size_t *, loff_t *);
  extern int proc_doulongvec_minmax(struct ctl_table *, int,
  				  void __user *, size_t *, loff_t *);
  extern int proc_doulongvec_ms_jiffies_minmax(struct ctl_table *table, int,
  				      void __user *, size_t *, loff_t *);
  extern int proc_do_large_bitmap(struct ctl_table *, int,
  				void __user *, size_t *, loff_t *);
  
  /*
   * Register a set of sysctl names by calling register_sysctl_table
   * with an initialised array of struct ctl_table's.  An entry with 
   * NULL procname terminates the table.  table->de will be
   * set up by the registration and need not be initialised in advance.
   *
   * sysctl names can be mirrored automatically under /proc/sys.  The
   * procname supplied controls /proc naming.
   *
   * The table's mode will be honoured both for sys_sysctl(2) and
   * proc-fs access.
   *
   * Leaf nodes in the sysctl tree will be represented by a single file
   * under /proc; non-leaf nodes will be represented by directories.  A
   * null procname disables /proc mirroring at this node.
   *
   * 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.
   * 
   * 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.
   */
  
  /* Support for userspace poll() to watch for changes */
  struct ctl_table_poll {
  	atomic_t event;
  	wait_queue_head_t wait;
  };
  
  static inline void *proc_sys_poll_event(struct ctl_table_poll *poll)
  {
  	return (void *)(unsigned long)atomic_read(&poll->event);
  }
  
  #define __CTL_TABLE_POLL_INITIALIZER(name) {				\
  	.event = ATOMIC_INIT(0),					\
  	.wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.wait) }
  
  #define DEFINE_CTL_TABLE_POLL(name)					\
  	struct ctl_table_poll name = __CTL_TABLE_POLL_INITIALIZER(name)
  
  /* A sysctl table is an array of struct ctl_table: */
  struct ctl_table 
  {
  	const char *procname;		/* Text ID for /proc/sys, or zero */
  	void *data;
  	int maxlen;
  	umode_t mode;
  	struct ctl_table *child;	/* Deprecated */
  	proc_handler *proc_handler;	/* Callback for text formatting */
  	struct ctl_table_poll *poll;
  	void *extra1;
  	void *extra2;
  } __randomize_layout;
  
  struct ctl_node {
  	struct rb_node node;
  	struct ctl_table_header *header;
  };
  
  /* struct ctl_table_header is used to maintain dynamic lists of
     struct ctl_table trees. */
  struct ctl_table_header
  {
  	union {
  		struct {
  			struct ctl_table *ctl_table;
  			int used;
  			int count;
  			int nreg;
  		};
  		struct rcu_head rcu;
  	};
  	struct completion *unregistering;
  	struct ctl_table *ctl_table_arg;
  	struct ctl_table_root *root;
  	struct ctl_table_set *set;
  	struct ctl_dir *parent;
  	struct ctl_node *node;
  	struct hlist_head inodes; /* head for proc_inode->sysctl_inodes */
  };
  
  struct ctl_dir {
  	/* Header must be at the start of ctl_dir */
  	struct ctl_table_header header;
  	struct rb_root root;
  };
  
  struct ctl_table_set {
  	int (*is_seen)(struct ctl_table_set *);
  	struct ctl_dir dir;
  };
  
  struct ctl_table_root {
  	struct ctl_table_set default_set;
  	struct ctl_table_set *(*lookup)(struct ctl_table_root *root);
  	void (*set_ownership)(struct ctl_table_header *head,
  			      struct ctl_table *table,
  			      kuid_t *uid, kgid_t *gid);
  	int (*permissions)(struct ctl_table_header *head, struct ctl_table *table);
  };
  
  /* struct ctl_path describes where in the hierarchy a table is added */
  struct ctl_path {
  	const char *procname;
  };
  
  #ifdef CONFIG_SYSCTL
  
  void proc_sys_poll_notify(struct ctl_table_poll *poll);
  
  extern void setup_sysctl_set(struct ctl_table_set *p,
  	struct ctl_table_root *root,
  	int (*is_seen)(struct ctl_table_set *));
  extern void retire_sysctl_set(struct ctl_table_set *set);
  
  struct ctl_table_header *__register_sysctl_table(
  	struct ctl_table_set *set,
  	const char *path, struct ctl_table *table);
  struct ctl_table_header *__register_sysctl_paths(
  	struct ctl_table_set *set,
  	const struct ctl_path *path, struct ctl_table *table);
  struct ctl_table_header *register_sysctl(const char *path, struct ctl_table *table);
  struct ctl_table_header *register_sysctl_table(struct ctl_table * table);
  struct ctl_table_header *register_sysctl_paths(const struct ctl_path *path,
  						struct ctl_table *table);
  
  void unregister_sysctl_table(struct ctl_table_header * table);
  
  extern int sysctl_init(void);
  
  extern struct ctl_table sysctl_mount_point[];
  
  #else /* CONFIG_SYSCTL */
  static inline struct ctl_table_header *register_sysctl_table(struct ctl_table * table)
  {
  	return NULL;
  }
  
  static inline struct ctl_table_header *register_sysctl_paths(
  			const struct ctl_path *path, struct ctl_table *table)
  {
  	return NULL;
  }
  
  static inline struct ctl_table_header *register_sysctl(const char *path, struct ctl_table *table)
  {
  	return NULL;
  }
  
  static inline void unregister_sysctl_table(struct ctl_table_header * table)
  {
  }
  
  static inline void setup_sysctl_set(struct ctl_table_set *p,
  	struct ctl_table_root *root,
  	int (*is_seen)(struct ctl_table_set *))
  {
  }
  
  #endif /* CONFIG_SYSCTL */
  
  int sysctl_max_threads(struct ctl_table *table, int write,
  		       void __user *buffer, size_t *lenp, loff_t *ppos);
  
  #endif /* _LINUX_SYSCTL_H */
  