linux/include/linux/kernfs.h

/* SPDX-License-Identifier: GPL-2.0-only */
/*
 * kernfs.h - pseudo filesystem decoupled from vfs locking
 */

#ifndef __LINUX_KERNFS_H
#define __LINUX_KERNFS_H

#include <linux/err.h>
#include <linux/list.h>
#include <linux/mutex.h>
#include <linux/idr.h>
#include <linux/lockdep.h>
#include <linux/rbtree.h>
#include <linux/atomic.h>
#include <linux/bug.h>
#include <linux/types.h>
#include <linux/uidgid.h>
#include <linux/wait.h>
#include <linux/rwsem.h>
#include <linux/cache.h>

struct file;
struct dentry;
struct iattr;
struct seq_file;
struct vm_area_struct;
struct vm_operations_struct;
struct super_block;
struct file_system_type;
struct poll_table_struct;
struct fs_context;

struct kernfs_fs_context;
struct kernfs_open_node;
struct kernfs_iattrs;

/*
 * NR_KERNFS_LOCK_BITS determines size (NR_KERNFS_LOCKS) of hash
 * table of locks.
 * Having a small hash table would impact scalability, since
 * more and more kernfs_node objects will end up using same lock
 * and having a very large hash table would waste memory.
 *
 * At the moment size of hash table of locks is being set based on
 * the number of CPUs as follows:
 *
 * NR_CPU      NR_KERNFS_LOCK_BITS      NR_KERNFS_LOCKS
 *   1                  1                       2
 *  2-3                 2                       4
 *  4-7                 4                       16
 *  8-15                6                       64
 *  16-31               8                       256
 *  32 and more         10                      1024
 *
 * The above relation between NR_CPU and number of locks is based
 * on some internal experimentation which involved booting qemu
 * with different values of smp, performing some sysfs operations
 * on all CPUs and observing how increase in number of locks impacts
 * completion time of these sysfs operations on each CPU.
 */
#ifdef CONFIG_SMP
#define NR_KERNFS_LOCK_BITS …
#else
#define NR_KERNFS_LOCK_BITS …
#endif

#define NR_KERNFS_LOCKS …

/*
 * There's one kernfs_open_file for each open file and one kernfs_open_node
 * for each kernfs_node with one or more open files.
 *
 * filp->private_data points to seq_file whose ->private points to
 * kernfs_open_file.
 *
 * kernfs_open_files are chained at kernfs_open_node->files, which is
 * protected by kernfs_global_locks.open_file_mutex[i].
 *
 * To reduce possible contention in sysfs access, arising due to single
 * locks, use an array of locks (e.g. open_file_mutex) and use kernfs_node
 * object address as hash keys to get the index of these locks.
 *
 * Hashed mutexes are safe to use here because operations using these don't
 * rely on global exclusion.
 *
 * In future we intend to replace other global locks with hashed ones as well.
 * kernfs_global_locks acts as a holder for all such hash tables.
 */
struct kernfs_global_locks { … };

enum kernfs_node_type { … };

#define KERNFS_TYPE_MASK …
#define KERNFS_FLAG_MASK …
#define KERNFS_MAX_USER_XATTRS …
#define KERNFS_USER_XATTR_SIZE_LIMIT …

enum kernfs_node_flag { … };

/* @flags for kernfs_create_root() */
enum kernfs_root_flag { … };

/* type-specific structures for kernfs_node union members */
struct kernfs_elem_dir { … };

struct kernfs_elem_symlink { … };

struct kernfs_elem_attr { … };

/*
 * kernfs_node - the building block of kernfs hierarchy.  Each and every
 * kernfs node is represented by single kernfs_node.  Most fields are
 * private to kernfs and shouldn't be accessed directly by kernfs users.
 *
 * As long as count reference is held, the kernfs_node itself is
 * accessible.  Dereferencing elem or any other outer entity requires
 * active reference.
 */
struct kernfs_node { … };

/*
 * kernfs_syscall_ops may be specified on kernfs_create_root() to support
 * syscalls.  These optional callbacks are invoked on the matching syscalls
 * and can perform any kernfs operations which don't necessarily have to be
 * the exact operation requested.  An active reference is held for each
 * kernfs_node parameter.
 */
struct kernfs_syscall_ops { … };

struct kernfs_node *kernfs_root_to_node(struct kernfs_root *root);

struct kernfs_open_file { … };

struct kernfs_ops { … };

/*
 * The kernfs superblock creation/mount parameter context.
 */
struct kernfs_fs_context { … };

#ifdef CONFIG_KERNFS

static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
{ … }

static inline ino_t kernfs_id_ino(u64 id)
{ … }

static inline u32 kernfs_id_gen(u64 id)
{ … }

static inline ino_t kernfs_ino(struct kernfs_node *kn)
{ … }

static inline ino_t kernfs_gen(struct kernfs_node *kn)
{ … }

/**
 * kernfs_enable_ns - enable namespace under a directory
 * @kn: directory of interest, should be empty
 *
 * This is to be called right after @kn is created to enable namespace
 * under it.  All children of @kn must have non-NULL namespace tags and
 * only the ones which match the super_block's tag will be visible.
 */
static inline void kernfs_enable_ns(struct kernfs_node *kn)
{ … }

/**
 * kernfs_ns_enabled - test whether namespace is enabled
 * @kn: the node to test
 *
 * Test whether namespace filtering is enabled for the children of @ns.
 */
static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
{ … }

int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen);
int kernfs_path_from_node(struct kernfs_node *root_kn, struct kernfs_node *kn,
			  char *buf, size_t buflen);
void pr_cont_kernfs_name(struct kernfs_node *kn);
void pr_cont_kernfs_path(struct kernfs_node *kn);
struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn);
struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
					   const char *name, const void *ns);
struct kernfs_node *kernfs_walk_and_get_ns(struct kernfs_node *parent,
					   const char *path, const void *ns);
void kernfs_get(struct kernfs_node *kn);
void kernfs_put(struct kernfs_node *kn);

struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry);
struct kernfs_root *kernfs_root_from_sb(struct super_block *sb);
struct inode *kernfs_get_inode(struct super_block *sb, struct kernfs_node *kn);

struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
				  struct super_block *sb);
struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
				       unsigned int flags, void *priv);
void kernfs_destroy_root(struct kernfs_root *root);

struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
					 const char *name, umode_t mode,
					 kuid_t uid, kgid_t gid,
					 void *priv, const void *ns);
struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
					    const char *name);
struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
					 const char *name, umode_t mode,
					 kuid_t uid, kgid_t gid,
					 loff_t size,
					 const struct kernfs_ops *ops,
					 void *priv, const void *ns,
					 struct lock_class_key *key);
struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
				       const char *name,
				       struct kernfs_node *target);
void kernfs_activate(struct kernfs_node *kn);
void kernfs_show(struct kernfs_node *kn, bool show);
void kernfs_remove(struct kernfs_node *kn);
void kernfs_break_active_protection(struct kernfs_node *kn);
void kernfs_unbreak_active_protection(struct kernfs_node *kn);
bool kernfs_remove_self(struct kernfs_node *kn);
int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
			     const void *ns);
int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
		     const char *new_name, const void *new_ns);
int kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr);
__poll_t kernfs_generic_poll(struct kernfs_open_file *of,
			     struct poll_table_struct *pt);
void kernfs_notify(struct kernfs_node *kn);

int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
		     void *value, size_t size);
int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
		     const void *value, size_t size, int flags);

const void *kernfs_super_ns(struct super_block *sb);
int kernfs_get_tree(struct fs_context *fc);
void kernfs_free_fs_context(struct fs_context *fc);
void kernfs_kill_sb(struct super_block *sb);

void kernfs_init(void);

struct kernfs_node *kernfs_find_and_get_node_by_id(struct kernfs_root *root,
						   u64 id);
#else	/* CONFIG_KERNFS */

static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
{ return 0; }	/* whatever */

static inline void kernfs_enable_ns(struct kernfs_node *kn) { }

static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
{ return false; }

static inline int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
{ return -ENOSYS; }

static inline int kernfs_path_from_node(struct kernfs_node *root_kn,
					struct kernfs_node *kn,
					char *buf, size_t buflen)
{ return -ENOSYS; }

static inline void pr_cont_kernfs_name(struct kernfs_node *kn) { }
static inline void pr_cont_kernfs_path(struct kernfs_node *kn) { }

static inline struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn)
{ return NULL; }

static inline struct kernfs_node *
kernfs_find_and_get_ns(struct kernfs_node *parent, const char *name,
		       const void *ns)
{ return NULL; }
static inline struct kernfs_node *
kernfs_walk_and_get_ns(struct kernfs_node *parent, const char *path,
		       const void *ns)
{ return NULL; }

static inline void kernfs_get(struct kernfs_node *kn) { }
static inline void kernfs_put(struct kernfs_node *kn) { }

static inline struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry)
{ return NULL; }

static inline struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
{ return NULL; }

static inline struct inode *
kernfs_get_inode(struct super_block *sb, struct kernfs_node *kn)
{ return NULL; }

static inline struct kernfs_root *
kernfs_create_root(struct kernfs_syscall_ops *scops, unsigned int flags,
		   void *priv)
{ return ERR_PTR(-ENOSYS); }

static inline void kernfs_destroy_root(struct kernfs_root *root) { }

static inline struct kernfs_node *
kernfs_create_dir_ns(struct kernfs_node *parent, const char *name,
		     umode_t mode, kuid_t uid, kgid_t gid,
		     void *priv, const void *ns)
{ return ERR_PTR(-ENOSYS); }

static inline struct kernfs_node *
__kernfs_create_file(struct kernfs_node *parent, const char *name,
		     umode_t mode, kuid_t uid, kgid_t gid,
		     loff_t size, const struct kernfs_ops *ops,
		     void *priv, const void *ns, struct lock_class_key *key)
{ return ERR_PTR(-ENOSYS); }

static inline struct kernfs_node *
kernfs_create_link(struct kernfs_node *parent, const char *name,
		   struct kernfs_node *target)
{ return ERR_PTR(-ENOSYS); }

static inline void kernfs_activate(struct kernfs_node *kn) { }

static inline void kernfs_remove(struct kernfs_node *kn) { }

static inline bool kernfs_remove_self(struct kernfs_node *kn)
{ return false; }

static inline int kernfs_remove_by_name_ns(struct kernfs_node *kn,
					   const char *name, const void *ns)
{ return -ENOSYS; }

static inline int kernfs_rename_ns(struct kernfs_node *kn,
				   struct kernfs_node *new_parent,
				   const char *new_name, const void *new_ns)
{ return -ENOSYS; }

static inline int kernfs_setattr(struct kernfs_node *kn,
				 const struct iattr *iattr)
{ return -ENOSYS; }

static inline __poll_t kernfs_generic_poll(struct kernfs_open_file *of,
					   struct poll_table_struct *pt)
{ return -ENOSYS; }

static inline void kernfs_notify(struct kernfs_node *kn) { }

static inline int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
				   void *value, size_t size)
{ return -ENOSYS; }

static inline int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
				   const void *value, size_t size, int flags)
{ return -ENOSYS; }

static inline const void *kernfs_super_ns(struct super_block *sb)
{ return NULL; }

static inline int kernfs_get_tree(struct fs_context *fc)
{ return -ENOSYS; }

static inline void kernfs_free_fs_context(struct fs_context *fc) { }

static inline void kernfs_kill_sb(struct super_block *sb) { }

static inline void kernfs_init(void) { }

#endif	/* CONFIG_KERNFS */

/**
 * kernfs_path - build full path of a given node
 * @kn: kernfs_node of interest
 * @buf: buffer to copy @kn's name into
 * @buflen: size of @buf
 *
 * If @kn is NULL result will be "(null)".
 *
 * Returns the length of the full path.  If the full length is equal to or
 * greater than @buflen, @buf contains the truncated path with the trailing
 * '\0'.  On error, -errno is returned.
 */
static inline int kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen)
{ … }

static inline struct kernfs_node *
kernfs_find_and_get(struct kernfs_node *kn, const char *name)
{ … }

static inline struct kernfs_node *
kernfs_walk_and_get(struct kernfs_node *kn, const char *path)
{ … }

static inline struct kernfs_node *
kernfs_create_dir(struct kernfs_node *parent, const char *name, umode_t mode,
		  void *priv)
{ … }

static inline int kernfs_remove_by_name(struct kernfs_node *parent,
					const char *name)
{ … }

static inline int kernfs_rename(struct kernfs_node *kn,
				struct kernfs_node *new_parent,
				const char *new_name)
{ … }

#endif	/* __LINUX_KERNFS_H */