/* 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/kernel.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/uidgid.h>
#include <linux/wait.h>

struct file;
struct dentry;
struct iattr;
struct seq_file;
struct vm_area_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;

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 *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_root {
        /* published fields */
        struct kernfs_node      *kn;
        unsigned int            flags;  /* KERNFS_ROOT_* flags */

        /* private fields, do not use outside kernfs proper */
        struct idr              ino_idr;
        u32                     last_id_lowbits;
        u32                     id_highbits;
        struct kernfs_syscall_ops *syscall_ops;

        /* list of kernfs_super_info of this root, protected by kernfs_rwsem */
        struct list_head        supers;

        wait_queue_head_t       deactivate_waitq;
};

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);

#ifdef CONFIG_DEBUG_LOCK_ALLOC
        struct lock_class_key   lockdep_key;
#endif
};

/*
 * 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 struct kernfs_node *
kernfs_create_file_ns(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 = NULL;

#ifdef CONFIG_DEBUG_LOCK_ALLOC
        key = (struct lock_class_key *)&ops->lockdep_key;
#endif
        return __kernfs_create_file(parent, name, mode, uid, gid,
                                    size, ops, priv, ns, key);
}

static inline struct kernfs_node *
kernfs_create_file(struct kernfs_node *parent, const char *name, umode_t mode,
                   loff_t size, const struct kernfs_ops *ops, void *priv)
{
        return kernfs_create_file_ns(parent, name, mode,
                                     GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
                                     size, ops, 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 */