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 /* 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 (2 * (ilog2(NR_CPUS < 32 ? NR_CPUS : 32)))
 #else
 #define NR_KERNFS_LOCK_BITS     1
 #endif
 
 #define NR_KERNFS_LOCKS     (1 << NR_KERNFS_LOCK_BITS)
 
 /*
  * 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 {
     struct mutex open_file_mutex[NR_KERNFS_LOCKS];
 };
 
 enum kernfs_node_type {
     KERNFS_DIR      = 0x0001,
     KERNFS_FILE     = 0x0002,
     KERNFS_LINK     = 0x0004,
 };
 
 #define KERNFS_TYPE_MASK        0x000f
 #define KERNFS_FLAG_MASK        ~KERNFS_TYPE_MASK
 #define KERNFS_MAX_USER_XATTRS      128
 #define KERNFS_USER_XATTR_SIZE_LIMIT    (128 << 10)
 
 enum kernfs_node_flag {
     KERNFS_ACTIVATED    = 0x0010,
     KERNFS_NS       = 0x0020,
     KERNFS_HAS_SEQ_SHOW = 0x0040,
     KERNFS_HAS_MMAP     = 0x0080,
     KERNFS_LOCKDEP      = 0x0100,
     KERNFS_SUICIDAL     = 0x0400,
     KERNFS_SUICIDED     = 0x0800,
     KERNFS_EMPTY_DIR    = 0x1000,
     KERNFS_HAS_RELEASE  = 0x2000,
 };
 
 /* @flags for kernfs_create_root() */
 enum kernfs_root_flag {
     /*
      * kernfs_nodes are created in the deactivated state and invisible.
      * They require explicit kernfs_activate() to become visible.  This
      * can be used to make related nodes become visible atomically
      * after all nodes are created successfully.
      */
     KERNFS_ROOT_CREATE_DEACTIVATED      = 0x0001,
 
     /*
      * For regular files, if the opener has CAP_DAC_OVERRIDE, open(2)
      * succeeds regardless of the RW permissions.  sysfs had an extra
      * layer of enforcement where open(2) fails with -EACCES regardless
      * of CAP_DAC_OVERRIDE if the permission doesn't have the
      * respective read or write access at all (none of S_IRUGO or
      * S_IWUGO) or the respective operation isn't implemented.  The
      * following flag enables that behavior.
      */
     KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK   = 0x0002,
 
     /*
      * The filesystem supports exportfs operation, so userspace can use
      * fhandle to access nodes of the fs.
      */
     KERNFS_ROOT_SUPPORT_EXPORTOP        = 0x0004,
 
     /*
      * Support user xattrs to be written to nodes rooted at this root.
      */
     KERNFS_ROOT_SUPPORT_USER_XATTR      = 0x0008,
 };
 
 /* type-specific structures for kernfs_node union members */
 struct kernfs_elem_dir {
     unsigned long       subdirs;
     /* children rbtree starts here and goes through kn->rb */
     struct rb_root      children;
 
     /*
      * The kernfs hierarchy this directory belongs to.  This fits
      * better directly in kernfs_node but is here to save space.
      */
     struct kernfs_root  *root;
     /*
      * Monotonic revision counter, used to identify if a directory
      * node has changed during negative dentry revalidation.
      */
     unsigned long       rev;
 };
 
 struct kernfs_elem_symlink {
     struct kernfs_node  *target_kn;
 };
 
 struct kernfs_elem_attr {
     const struct kernfs_ops *ops;
     struct kernfs_open_node __rcu   *open;
     loff_t          size;
     struct kernfs_node  *notify_next;   /* for kernfs_notify() */
 };
 
 /*
  * 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 {
     atomic_t        count;
     atomic_t        active;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
     struct lockdep_map  dep_map;
 #endif
     /*
      * Use kernfs_get_parent() and kernfs_name/path() instead of
      * accessing the following two fields directly.  If the node is
      * never moved to a different parent, it is safe to access the
      * parent directly.
      */
     struct kernfs_node  *parent;
     const char      *name;
 
     struct rb_node      rb;
 
     const void      *ns;    /* namespace tag */
     unsigned int        hash;   /* ns + name hash */
     union {
         struct kernfs_elem_dir      dir;
         struct kernfs_elem_symlink  symlink;
         struct kernfs_elem_attr     attr;
     };
 
     void            *priv;
 
     /*
      * 64bit unique ID.  On 64bit ino setups, id is the ino.  On 32bit,
      * the low 32bits are ino and upper generation.
      */
     u64         id;
 
     unsigned short      flags;
     umode_t         mode;
     struct kernfs_iattrs    *iattr;
 };
 
 /*
  * 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 {
     int (*show_options)(struct seq_file *sf, struct kernfs_root *root);
 
     int (*mkdir)(struct kernfs_node *parent, const char *name,
              umode_t mode);
     int (*rmdir)(struct kernfs_node *kn);
     int (*rename)(struct kernfs_node *kn, struct kernfs_node *new_parent,
               const char *new_name);
     int (*show_path)(struct seq_file *sf, struct kernfs_node *kn,
              struct kernfs_root *root);
 };
 
 struct kernfs_node *kernfs_root_to_node(struct kernfs_root *root);
 
 struct kernfs_open_file {
     /* published fields */
     struct kernfs_node  *kn;
     struct file     *file;
     struct seq_file     *seq_file;
     void            *priv;
 
     /* private fields, do not use outside kernfs proper */
     struct mutex        mutex;
     struct mutex        prealloc_mutex;
     int         event;
     struct list_head    list;
     char            *prealloc_buf;
 
     size_t          atomic_write_len;
     bool            mmapped:1;
     bool            released:1;
     const struct vm_operations_struct *vm_ops;
 };
 
 struct kernfs_ops {
     /*
      * Optional open/release methods.  Both are called with
      * @of->seq_file populated.
      */
     int (*open)(struct kernfs_open_file *of);
     void (*release)(struct kernfs_open_file *of);
 
     /*
      * Read is handled by either seq_file or raw_read().
      *
      * If seq_show() is present, seq_file path is active.  Other seq
      * operations are optional and if not implemented, the behavior is
      * equivalent to single_open().  @sf->private points to the
      * associated kernfs_open_file.
      *
      * read() is bounced through kernel buffer and a read larger than
      * PAGE_SIZE results in partial operation of PAGE_SIZE.
      */
     int (*seq_show)(struct seq_file *sf, void *v);
 
     void *(*seq_start)(struct seq_file *sf, loff_t *ppos);
     void *(*seq_next)(struct seq_file *sf, void *v, loff_t *ppos);
     void (*seq_stop)(struct seq_file *sf, void *v);
 
     ssize_t (*read)(struct kernfs_open_file *of, char *buf, size_t bytes,
             loff_t off);
 
     /*
      * write() is bounced through kernel buffer.  If atomic_write_len
      * is not set, a write larger than PAGE_SIZE results in partial
      * operations of PAGE_SIZE chunks.  If atomic_write_len is set,
      * writes upto the specified size are executed atomically but
      * larger ones are rejected with -E2BIG.
      */
     size_t atomic_write_len;
     /*
      * "prealloc" causes a buffer to be allocated at open for
      * all read/write requests.  As ->seq_show uses seq_read()
      * which does its own allocation, it is incompatible with
      * ->prealloc.  Provide ->read and ->write with ->prealloc.
      */
     bool prealloc;
     ssize_t (*write)(struct kernfs_open_file *of, char *buf, size_t bytes,
              loff_t off);
 
     __poll_t (*poll)(struct kernfs_open_file *of,
              struct poll_table_struct *pt);
 
     int (*mmap)(struct kernfs_open_file *of, struct vm_area_struct *vma);
 };
 
 /*
  * The kernfs superblock creation/mount parameter context.
  */
 struct kernfs_fs_context {
     struct kernfs_root  *root;      /* Root of the hierarchy being mounted */
     void            *ns_tag;    /* Namespace tag of the mount (or NULL) */
     unsigned long       magic;      /* File system specific magic number */
 
     /* The following are set/used by kernfs_mount() */
     bool            new_sb_created; /* Set to T if we allocated a new sb */
 };
 
 #ifdef CONFIG_KERNFS
 
 static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
 {
     return kn->flags & KERNFS_TYPE_MASK;
 }
 
 static inline ino_t kernfs_id_ino(u64 id)
 {
     /* id is ino if ino_t is 64bit; otherwise, low 32bits */
     if (sizeof(ino_t) >= sizeof(u64))
         return id;
     else
         return (u32)id;
 }
 
 static inline u32 kernfs_id_gen(u64 id)
 {
     /* gen is fixed at 1 if ino_t is 64bit; otherwise, high 32bits */
     if (sizeof(ino_t) >= sizeof(u64))
         return 1;
     else
         return id >> 32;
 }
 
 static inline ino_t kernfs_ino(struct kernfs_node *kn)
 {
     return kernfs_id_ino(kn->id);
 }
 
 static inline ino_t kernfs_gen(struct kernfs_node *kn)
 {
     return kernfs_id_gen(kn->id);
 }
 
 /**
  * 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)
 {
     WARN_ON_ONCE(kernfs_type(kn) != KERNFS_DIR);
     WARN_ON_ONCE(!RB_EMPTY_ROOT(&kn->dir.children));
     kn->flags |= KERNFS_NS;
 }
 
 /**
  * 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)
 {
     return kn->flags & KERNFS_NS;
 }
 
 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_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 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)
 {
     return kernfs_path_from_node(kn, NULL, buf, buflen);
 }
 
 static inline struct kernfs_node *
 kernfs_find_and_get(struct kernfs_node *kn, const char *name)
 {
     return kernfs_find_and_get_ns(kn, name, NULL);
 }
 
 static inline struct kernfs_node *
 kernfs_walk_and_get(struct kernfs_node *kn, const char *path)
 {
     return kernfs_walk_and_get_ns(kn, path, NULL);
 }
 
 static inline struct kernfs_node *
 kernfs_create_dir(struct kernfs_node *parent, const char *name, umode_t mode,
           void *priv)
 {
     return kernfs_create_dir_ns(parent, name, mode,
                     GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
                     priv, NULL);
 }
 
 static inline int kernfs_remove_by_name(struct kernfs_node *parent,
                     const char *name)
 {
     return kernfs_remove_by_name_ns(parent, name, NULL);
 }
 
 static inline int kernfs_rename(struct kernfs_node *kn,
                 struct kernfs_node *new_parent,
                 const char *new_name)
 {
     return kernfs_rename_ns(kn, new_parent, new_name, NULL);
 }
 
 #endif  /* __LINUX_KERNFS_H */

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