/*
    FUSE: Filesystem in Userspace
    Copyright (C) 2001-2006  Miklos Szeredi <miklos@szeredi.hu>

    This program can be distributed under the terms of the GNU LGPL.
    See the file COPYING.LIB.
*/

#ifndef _FUSE_LOWLEVEL_H_
#define _FUSE_LOWLEVEL_H_

/* =========================================================== *
 * Low level API                                               *
 * =========================================================== */

/* IMPORTANT: you should define FUSE_USE_VERSION before including this
   header.  To use the newest API define it to 26 (recommended for any
   new application), to use the old API define it to 24 (default) or
   25 */

#ifndef FUSE_USE_VERSION
#define FUSE_USE_VERSION 24
#endif

#include "fuse_common.h"

#include <utime.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/statvfs.h>
#include <sys/uio.h>

#ifdef __cplusplus
extern "C" {
#endif

/* ----------------------------------------------------------- *
 * Miscellaneous definitions                                   *
 * ----------------------------------------------------------- */

/** The node ID of the root inode */
#define FUSE_ROOT_ID 1

/** Inode number type */
typedef unsigned long fuse_ino_t;

/** Request pointer type */
typedef struct fuse_req *fuse_req_t;

/**
 * Session
 *
 * This provides hooks for processing requests, and exiting
 */
struct fuse_session;

/**
 * Channel
 *
 * A communication channel, providing hooks for sending and receiving
 * messages
 */
struct fuse_chan;

/** Directory entry parameters supplied to fuse_reply_entry() */
struct fuse_entry_param {
    /** Unique inode number
     *
     * In lookup, zero means negative entry (from version 2.5)
     * Returning ENOENT also means negative entry, but by setting zero
     * ino the kernel may cache negative entries for entry_timeout
     * seconds.
     */
    fuse_ino_t ino;

    /** The ino/generation pair should be unique for the filesystem's
        lifetime */
    unsigned long generation;

    /** Inode attributes */
    struct stat attr;

    /** Validity timeout (in seconds) for the attributes */
    double attr_timeout;

    /** Validity timeout (in seconds) for the name */
    double entry_timeout;
};

/** Additional context associated with requests */
struct fuse_ctx {
    /** User ID of the calling process */
    uid_t uid;

    /** Group ID of the calling process */
    gid_t gid;

    /** Thread ID of the calling process */
    pid_t pid;
};

/* 'to_set' flags in setattr */
#define FUSE_SET_ATTR_MODE	(1 << 0)
#define FUSE_SET_ATTR_UID	(1 << 1)
#define FUSE_SET_ATTR_GID	(1 << 2)
#define FUSE_SET_ATTR_SIZE	(1 << 3)
#define FUSE_SET_ATTR_ATIME	(1 << 4)
#define FUSE_SET_ATTR_MTIME	(1 << 5)

/* ----------------------------------------------------------- *
 * Request methods and replies                                 *
 * ----------------------------------------------------------- */

/**
 * Low level filesystem operations
 *
 * Most of the methods (with the exception of init and destroy)
 * receive a request handle (fuse_req_t) as their first argument.
 * This handle must be passed to one of the specified reply functions.
 *
 * This may be done inside the method invocation, or after the call
 * has returned.  The request handle is valid until one of the reply
 * functions is called.
 *
 * Other pointer arguments (name, fuse_file_info, etc) are not valid
 * after the call has returned, so if they are needed later, their
 * contents have to be copied.
 *
 * The filesystem sometimes needs to handle a return value of -ENOENT
 * from the reply function, which means, that the request was
 * interrupted, and the reply discarded.  For example if
 * fuse_reply_open() return -ENOENT means, that the release method for
 * this file will not be called.
 */
struct fuse_lowlevel_ops {
    /**
     * Initialize filesystem
     *
     * Called before any other filesystem method
     *
     * There's no reply to this function
     *
     * @param userdata the user data passed to fuse_lowlevel_new()
     */
    void (*init) (void *userdata, struct fuse_conn_info *conn);

    /**
     * Clean up filesystem
     *
     * Called on filesystem exit
     *
     * There's no reply to this function
     *
     * @param userdata the user data passed to fuse_lowlevel_new()
     */
    void (*destroy) (void *userdata);

    /**
     * Look up a directory entry by name
     *
     * Valid replies:
     *   fuse_reply_entry
     *   fuse_reply_err
     *
     * @param req request handle
     * @param parent inode number of the parent directory
     * @param name the name to look up
     */
    void (*lookup) (fuse_req_t req, fuse_ino_t parent, const char *name);

    /**
     * Forget about an inode
     *
     * The nlookup parameter indicates the number of lookups
     * previously performed on this inode.
     *
     * If the filesystem implements inode lifetimes, it is recommended
     * that inodes acquire a single reference on each lookup, and lose
     * nlookup references on each forget.
     *
     * The filesystem may ignore forget calls, if the inodes don't
     * need to have a limited lifetime.
     *
     * On unmount it is not guaranteed, that all referenced inodes
     * will receive a forget message.
     *
     * Valid replies:
     *   fuse_reply_none
     *
     * @param req request handle
     * @param ino the inode number
     * @param nlookup the number of lookups to forget
     */
    void (*forget) (fuse_req_t req, fuse_ino_t ino, unsigned long nlookup);

    /**
     * Get file attributes
     *
     * Valid replies:
     *   fuse_reply_attr
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param fi for future use, currently always NULL
     */
    void (*getattr) (fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi);

    /**
     * Set file attributes
     *
     * In the 'attr' argument only members indicated by the 'to_set'
     * bitmask contain valid values.  Other members contain undefined
     * values.
     *
     * If the setattr was invoked from the ftruncate() system call
     * under Linux kernel versions 2.6.15 or later, the fi->fh will
     * contain the value set by the open method or will be undefined
     * if the open method didn't set any value.  Otherwise (not
     * ftruncate call, or kernel version earlier than 2.6.15) the fi
     * parameter will be NULL.
     *
     * Valid replies:
     *   fuse_reply_attr
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param attr the attributes
     * @param to_set bit mask of attributes which should be set
     * @param fi file information, or NULL
     *
     * Changed in version 2.5:
     *     file information filled in for ftruncate
     */
    void (*setattr) (fuse_req_t req, fuse_ino_t ino, struct stat *attr,
                    int to_set, struct fuse_file_info *fi);

    /**
     * Read symbolic link
     *
     * Valid replies:
     *   fuse_reply_readlink
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     */
    void (*readlink) (fuse_req_t req, fuse_ino_t ino);

    /**
     * Create file node
     *
     * Create a regular file, character device, block device, fifo or
     * socket node.
     *
     * Valid replies:
     *   fuse_reply_entry
     *   fuse_reply_err
     *
     * @param req request handle
     * @param parent inode number of the parent directory
     * @param name to create
     * @param mode file type and mode with which to create the new file
     * @param rdev the device number (only valid if created file is a device)
     */
    void (*mknod) (fuse_req_t req, fuse_ino_t parent, const char *name,
                   mode_t mode, dev_t rdev);

    /**
     * Create a directory
     *
     * Valid replies:
     *   fuse_reply_entry
     *   fuse_reply_err
     *
     * @param req request handle
     * @param parent inode number of the parent directory
     * @param name to create
     * @param mode with which to create the new file
     */
    void (*mkdir) (fuse_req_t req, fuse_ino_t parent, const char *name,
                   mode_t mode);

    /**
     * Remove a file
     *
     * Valid replies:
     *   fuse_reply_err
     *
     * @param req request handle
     * @param parent inode number of the parent directory
     * @param name to remove
     */
    void (*unlink) (fuse_req_t req, fuse_ino_t parent, const char *name);

    /**
     * Remove a directory
     *
     * Valid replies:
     *   fuse_reply_err
     *
     * @param req request handle
     * @param parent inode number of the parent directory
     * @param name to remove
     */
    void (*rmdir) (fuse_req_t req, fuse_ino_t parent, const char *name);

    /**
     * Create a symbolic link
     *
     * Valid replies:
     *   fuse_reply_entry
     *   fuse_reply_err
     *
     * @param req request handle
     * @param link the contents of the symbolic link
     * @param parent inode number of the parent directory
     * @param name to create
     */
    void (*symlink) (fuse_req_t req, const char *link, fuse_ino_t parent,
                     const char *name);

    /** Rename a file
     *
     * Valid replies:
     *   fuse_reply_err
     *
     * @param req request handle
     * @param parent inode number of the old parent directory
     * @param name old name
     * @param newparent inode number of the new parent directory
     * @param newname new name
     */
    void (*rename) (fuse_req_t req, fuse_ino_t parent, const char *name,
                    fuse_ino_t newparent, const char *newname);

    /**
     * Create a hard link
     *
     * Valid replies:
     *   fuse_reply_entry
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the old inode number
     * @param newparent inode number of the new parent directory
     * @param newname new name to create
     */
    void (*link) (fuse_req_t req, fuse_ino_t ino, fuse_ino_t newparent,
                  const char *newname);

    /**
     * Open a file
     *
     * Open flags (with the exception of O_CREAT, O_EXCL, O_NOCTTY and
     * O_TRUNC) are available in fi->flags.
     *
     * Filesystem may store an arbitrary file handle (pointer, index,
     * etc) in fi->fh, and use this in other all other file operations
     * (read, write, flush, release, fsync).
     *
     * Filesystem may also implement stateless file I/O and not store
     * anything in fi->fh.
     *
     * There are also some flags (direct_io, keep_cache) which the
     * filesystem may set in fi, to change the way the file is opened.
     * See fuse_file_info structure in <fuse_common.h> for more details.
     *
     * Valid replies:
     *   fuse_reply_open
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param fi file information
     */
    void (*open) (fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi);

    /**
     * Read data
     *
     * Read should send exactly the number of bytes requested except
     * on EOF or error, otherwise the rest of the data will be
     * substituted with zeroes.  An exception to this is when the file
     * has been opened in 'direct_io' mode, in which case the return
     * value of the read system call will reflect the return value of
     * this operation.
     *
     * fi->fh will contain the value set by the open method, or will
     * be undefined if the open method didn't set any value.
     *
     * Valid replies:
     *   fuse_reply_buf
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param size number of bytes to read
     * @param off offset to read from
     * @param fi file information
     */
    void (*read) (fuse_req_t req, fuse_ino_t ino, size_t size, off_t off,
                  struct fuse_file_info *fi);

    /**
     * Write data
     *
     * Write should return exactly the number of bytes requested
     * except on error.  An exception to this is when the file has
     * been opened in 'direct_io' mode, in which case the return value
     * of the write system call will reflect the return value of this
     * operation.
     *
     * fi->fh will contain the value set by the open method, or will
     * be undefined if the open method didn't set any value.
     *
     * Valid replies:
     *   fuse_reply_write
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param buf data to write
     * @param size number of bytes to write
     * @param off offset to write to
     * @param fi file information
     */
    void (*write) (fuse_req_t req, fuse_ino_t ino, const char *buf,
                   size_t size, off_t off, struct fuse_file_info *fi);

    /**
     * Flush method
     *
     * This is called on each close() of the opened file.
     *
     * Since file descriptors can be duplicated (dup, dup2, fork), for
     * one open call there may be many flush calls.
     *
     * Filesystems shouldn't assume that flush will always be called
     * after some writes, or that if will be called at all.
     *
     * fi->fh will contain the value set by the open method, or will
     * be undefined if the open method didn't set any value.
     *
     * NOTE: the name of the method is misleading, since (unlike
     * fsync) the filesystem is not forced to flush pending writes.
     * One reason to flush data, is if the filesystem wants to return
     * write errors.
     *
     * If the filesystem supports file locking operations (setlk,
     * getlk) it should remove all locks belonging to 'fi->owner'.
     *
     * Valid replies:
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param fi file information
     */
    void (*flush) (fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi);

    /**
     * Release an open file
     *
     * Release is called when there are no more references to an open
     * file: all file descriptors are closed and all memory mappings
     * are unmapped.
     *
     * For every open call there will be exactly one release call.
     *
     * The filesystem may reply with an error, but error values are
     * not returned to close() or munmap() which triggered the
     * release.
     *
     * fi->fh will contain the value set by the open method, or will
     * be undefined if the open method didn't set any value.
     * fi->flags will contain the same flags as for open.
     *
     * Valid replies:
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param fi file information
     */
    void (*release) (fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi);

    /**
     * Synchronize file contents
     *
     * If the datasync parameter is non-zero, then only the user data
     * should be flushed, not the meta data.
     *
     * Valid replies:
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param datasync flag indicating if only data should be flushed
     * @param fi file information
     */
    void (*fsync) (fuse_req_t req, fuse_ino_t ino, int datasync,
                   struct fuse_file_info *fi);

    /**
     * Open a directory
     *
     * Filesystem may store an arbitrary file handle (pointer, index,
     * etc) in fi->fh, and use this in other all other directory
     * stream operations (readdir, releasedir, fsyncdir).
     *
     * Filesystem may also implement stateless directory I/O and not
     * store anything in fi->fh, though that makes it impossible to
     * implement standard conforming directory stream operations in
     * case the contents of the directory can change between opendir
     * and releasedir.
     *
     * Valid replies:
     *   fuse_reply_open
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param fi file information
     */
    void (*opendir) (fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi);

    /**
     * Read directory
     *
     * Send a buffer filled using fuse_add_direntry(), with size not
     * exceeding the requested size.  Send an empty buffer on end of
     * stream.
     *
     * fi->fh will contain the value set by the opendir method, or
     * will be undefined if the opendir method didn't set any value.
     *
     * Valid replies:
     *   fuse_reply_buf
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param size maximum number of bytes to send
     * @param off offset to continue reading the directory stream
     * @param fi file information
     */
    void (*readdir) (fuse_req_t req, fuse_ino_t ino, size_t size, off_t off,
                     struct fuse_file_info *fi);

    /**
     * Release an open directory
     *
     * For every opendir call there will be exactly one releasedir
     * call.
     *
     * Any errors sent by releasedir will be ignored.
     *
     * fi->fh will contain the value set by the opendir method, or
     * will be undefined if the opendir method didn't set any value.
     *
     * Valid replies:
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param fi file information
     */
    void (*releasedir) (fuse_req_t req, fuse_ino_t ino,
                        struct fuse_file_info *fi);

    /**
     * Synchronize directory contents
     *
     * If the datasync parameter is non-zero, then only the directory
     * contents should be flushed, not the meta data.
     *
     * fi->fh will contain the value set by the opendir method, or
     * will be undefined if the opendir method didn't set any value.
     *
     * Valid replies:
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param datasync flag indicating if only data should be flushed
     * @param fi file information
     */
    void (*fsyncdir) (fuse_req_t req, fuse_ino_t ino, int datasync,
                      struct fuse_file_info *fi);

    /**
     * Get file system statistics
     *
     * Valid replies:
     *   fuse_reply_statfs
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number, zero means "undefined"
     */
    void (*statfs) (fuse_req_t req, fuse_ino_t ino);

    /**
     * Set an extended attribute
     *
     * Valid replies:
     *   fuse_reply_err
     */
    void (*setxattr) (fuse_req_t req, fuse_ino_t ino, const char *name,
                      const char *value, size_t size, int flags);

    /**
     * Get an extended attribute
     *
     * If size is zero, the size of the value should be sent with
     * fuse_reply_xattr.
     *
     * If the size is non-zero, and the value fits in the buffer, the
     * value should be sent with fuse_reply_buf.
     *
     * If the size is too small for the value, the ERANGE error should
     * be sent.
     *
     * Valid replies:
     *   fuse_reply_buf
     *   fuse_reply_xattr
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param name of the extended attribute
     * @param size maximum size of the value to send
     */
    void (*getxattr) (fuse_req_t req, fuse_ino_t ino, const char *name,
                      size_t size);

    /**
     * List extended attribute names
     *
     * If size is zero, the total size of the attribute list should be
     * sent with fuse_reply_xattr.
     *
     * If the size is non-zero, and the null character separated
     * attribute list fits in the buffer, the list should be sent with
     * fuse_reply_buf.
     *
     * If the size is too small for the list, the ERANGE error should
     * be sent.
     *
     * Valid replies:
     *   fuse_reply_buf
     *   fuse_reply_xattr
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param size maximum size of the list to send
     */
    void (*listxattr) (fuse_req_t req, fuse_ino_t ino, size_t size);

    /**
     * Remove an extended attribute
     *
     * Valid replies:
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param name of the extended attribute
     */
    void (*removexattr) (fuse_req_t req, fuse_ino_t ino, const char *name);

    /**
     * Check file access permissions
     *
     * This will be called for the access() system call.  If the
     * 'default_permissions' mount option is given, this method is not
     * called.
     *
     * This method is not called under Linux kernel versions 2.4.x
     *
     * Introduced in version 2.5
     *
     * Valid replies:
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param mask requested access mode
     */
    void (*access) (fuse_req_t req, fuse_ino_t ino, int mask);

    /**
     * Create and open a file
     *
     * If the file does not exist, first create it with the specified
     * mode, and then open it.
     *
     * Open flags (with the exception of O_NOCTTY) are available in
     * fi->flags.
     *
     * Filesystem may store an arbitrary file handle (pointer, index,
     * etc) in fi->fh, and use this in other all other file operations
     * (read, write, flush, release, fsync).
     *
     * There are also some flags (direct_io, keep_cache) which the
     * filesystem may set in fi, to change the way the file is opened.
     * See fuse_file_info structure in <fuse_common.h> for more details.
     *
     * If this method is not implemented or under Linux kernel
     * versions earlier than 2.6.15, the mknod() and open() methods
     * will be called instead.
     *
     * Introduced in version 2.5
     *
     * Valid replies:
     *   fuse_reply_create
     *   fuse_reply_err
     *
     * @param req request handle
     * @param parent inode number of the parent directory
     * @param name to create
     * @param mode file type and mode with which to create the new file
     * @param fi file information
     */
    void (*create) (fuse_req_t req, fuse_ino_t parent, const char *name,
                    mode_t mode, struct fuse_file_info *fi);

    /**
     * Test for a POSIX file lock
     *
     * Introduced in version 2.6
     *
     * Valid replies:
     *   fuse_reply_lock
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param fi file information
     * @param lock the region/type to test
     */
    void (*getlk) (fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi,
                   struct flock *lock);

    /**
     * Acquire, modify or release a POSIX file lock
     *
     * For POSIX threads (NPTL) there's a 1-1 relation between pid and
     * owner, but otherwise this is not always the case.  For checking
     * lock ownership, 'fi->owner' must be used.  The l_pid field in
     * 'struct flock' should only be used to fill in this field in
     * getlk().
     *
     * Note: if the locking methods are not implemented, the kernel
     * will still allow file locking to work locally.  Hence these are
     * only interesting for network filesystems and similar.
     *
     * Introduced in version 2.6
     *
     * Valid replies:
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param fi file information
     * @param lock the region/type to test
     * @param sleep locking operation may sleep
     */
    void (*setlk) (fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi,
                   struct flock *lock, int sleep);

    /**
     * Map block index within file to block index within device
     *
     * Note: This makes sense only for block device backed filesystems
     * mounted with the 'blkdev' option
     *
     * Introduced in version 2.6
     *
     * Valid replies:
     *   fuse_reply_bmap
     *   fuse_reply_err
     *
     * @param req request handle
     * @param ino the inode number
     * @param blocksize unit of block index
     * @param idx block index within file
     */
    void (*bmap) (fuse_req_t req, fuse_ino_t ino, size_t blocksize,
                  uint64_t idx);
};

/**
 * Reply with an error code or success
 *
 * Possible requests:
 *   all except forget
 *
 * unlink, rmdir, rename, flush, release, fsync, fsyncdir, setxattr,
 * removexattr and setlk may send a zero code
 *
 * @param req request handle
 * @param err the positive error value, or zero for success
 * @return zero for success, -errno for failure to send reply
 */
int fuse_reply_err(fuse_req_t req, int err);

/**
 * Don't send reply
 *
 * Possible requests:
 *   forget
 *
 * @param req request handle
 */
void fuse_reply_none(fuse_req_t req);

/**
 * Reply with a directory entry
 *
 * Possible requests:
 *   lookup, mknod, mkdir, symlink, link
 *
 * @param req request handle
 * @param e the entry parameters
 * @return zero for success, -errno for failure to send reply
 */
int fuse_reply_entry(fuse_req_t req, const struct fuse_entry_param *e);

/**
 * Reply with a directory entry and open parameters
 *
 * currently the following members of 'fi' are used:
 *   fh, direct_io, keep_cache
 *
 * Possible requests:
 *   create
 *
 * @param req request handle
 * @param e the entry parameters
 * @param fi file information
 * @return zero for success, -errno for failure to send reply
 */
int fuse_reply_create(fuse_req_t req, const struct fuse_entry_param *e,
                      const struct fuse_file_info *fi);

/**
 * Reply with attributes
 *
 * Possible requests:
 *   getattr, setattr
 *
 * @param req request handle
 * @param the attributes
 * @param attr_timeout  validity timeout (in seconds) for the attributes
 * @return zero for success, -errno for failure to send reply
 */
int fuse_reply_attr(fuse_req_t req, const struct stat *attr,
                    double attr_timeout);

/**
 * Reply with the contents of a symbolic link
 *
 * Possible requests:
 *   readlink
 *
 * @param req request handle
 * @param link symbolic link contents
 * @return zero for success, -errno for failure to send reply
 */
int fuse_reply_readlink(fuse_req_t req, const char *link);

/**
 * Reply with open parameters
 *
 * currently the following members of 'fi' are used:
 *   fh, direct_io, keep_cache
 *
 * Possible requests:
 *   open, opendir
 *
 * @param req request handle
 * @param fi file information
 * @return zero for success, -errno for failure to send reply
 */
int fuse_reply_open(fuse_req_t req, const struct fuse_file_info *fi);

/**
 * Reply with number of bytes written
 *
 * Possible requests:
 *   write
 *
 * @param req request handle
 * @param count the number of bytes written
 * @return zero for success, -errno for failure to send reply
 */
int fuse_reply_write(fuse_req_t req, size_t count);

/**
 * Reply with data
 *
 * Possible requests:
 *   read, readdir, getxattr, listxattr
 *
 * @param req request handle
 * @param buf buffer containing data
 * @param size the size of data in bytes
 * @return zero for success, -errno for failure to send reply
 */
int fuse_reply_buf(fuse_req_t req, const char *buf, size_t size);

/**
 * Reply with filesystem statistics
 *
 * Possible requests:
 *   statfs
 *
 * @param req request handle
 * @param stbuf filesystem statistics
 * @return zero for success, -errno for failure to send reply
 */
int fuse_reply_statfs(fuse_req_t req, const struct statvfs *stbuf);

/**
 * Reply with needed buffer size
 *
 * Possible requests:
 *   getxattr, listxattr
 *
 * @param req request handle
 * @param count the buffer size needed in bytes
 * @return zero for success, -errno for failure to send reply
 */
int fuse_reply_xattr(fuse_req_t req, size_t count);

/**
 * Reply with file lock information
 *
 * Possible requests:
 *   getlk
 *
 * @param req request handle
 * @param lock the lock information
 * @return zero for success, -errno for failure to send reply
 */
int fuse_reply_lock(fuse_req_t req, struct flock *lock);

/**
 * Reply with block index
 *
 * Possible requests:
 *   bmap
 *
 * @param req request handle
 * @param idx block index within device 
 * @return zero for success, -errno for failure to send reply
 */
int fuse_reply_bmap(fuse_req_t req, uint64_t idx);

/* ----------------------------------------------------------- *
 * Filling a buffer in readdir                                 *
 * ----------------------------------------------------------- */

/**
 * Add a directory entry to the buffer
 *
 * Buffer needs to be large enough to hold the entry.  Of it's not,
 * then the entry is not filled in but the size of the entry is still
 * returned.  The caller can check this by comparing the bufsize
 * parameter with the returned entry size.  If the entry size is
 * larger than the buffer size, the operation failed.
 *
 * From the 'stbuf' argument the st_ino field and bits 12-15 of the
 * st_mode field are used.  The other fields are ignored.
 *
 * Note: offsets do not necessarily represent physical offsets, and
 * could be any marker, that enables the implementation to find a
 * specific point in the directory stream.
 *
 * @param req request handle
 * @param buf the point where the new entry will be added to the buffer
 * @param bufsize remaining size of the buffer
 * @param the name of the entry
 * @param stbuf the file attributes
 * @param off the offset of the next entry
 * @return the space needed for the entry
 */
size_t fuse_add_direntry(fuse_req_t req, char *buf, size_t bufsize,
                         const char *name, const struct stat *stbuf,
                         off_t off);

/* ----------------------------------------------------------- *
 * Utility functions                                           *
 * ----------------------------------------------------------- */

/**
 * Get the userdata from the request
 *
 * @param req request handle
 * @return the user data passed to fuse_lowlevel_new()
 */
void *fuse_req_userdata(fuse_req_t req);

/**
 * Get the context from the request
 *
 * The pointer returned by this function will only be valid for the
 * request's lifetime
 *
 * @param req request handle
 * @return the context structure
 */
const struct fuse_ctx *fuse_req_ctx(fuse_req_t req);

/**
 * Callback function for an interrupt
 *
 * @param req interrupted request
 * @param data user data
 */
typedef void (*fuse_interrupt_func_t)(fuse_req_t req, void *data);

/**
 * Register/unregister callback for an interrupt
 *
 * If an interrupt has already happened, then the callback function is
 * called from within this function, hence it's not possible for
 * interrupts to be lost.
 *
 * @param req request handle
 * @param func the callback function or NULL for unregister
 * @parm data user data passed to the callback function
 */
void fuse_req_interrupt_func(fuse_req_t req, fuse_interrupt_func_t func,
                             void *data);

/**
 * Check if a request has already been interrupted
 *
 * @param req request handle
 * @return 1 if the request has been interrupted, 0 otherwise
 */
int fuse_req_interrupted(fuse_req_t req);

/* ----------------------------------------------------------- *
 * Filesystem setup                                            *
 * ----------------------------------------------------------- */

/* Deprecated, don't use */
int fuse_lowlevel_is_lib_option(const char *opt);

/**
 * Create a low level session
 *
 * @param args argument vector
 * @param op the low level filesystem operations
 * @param op_size sizeof(struct fuse_lowlevel_ops)
 * @param userdata user data
 * @return the created session object, or NULL on failure
 */
struct fuse_session *fuse_lowlevel_new(struct fuse_args *args,
                                       const struct fuse_lowlevel_ops *op,
                                       size_t op_size, void *userdata);

/* ----------------------------------------------------------- *
 * Session interface                                           *
 * ----------------------------------------------------------- */

/**
 * Session operations
 *
 * This is used in session creation
 */
struct fuse_session_ops {
    /**
     * Hook to process a request (mandatory)
     *
     * @param data user data passed to fuse_session_new()
     * @param buf buffer containing the raw request
     * @param len request length
     * @param ch channel on which the request was received
     */
    void (*process) (void *data, const char *buf, size_t len,
                     struct fuse_chan *ch);

    /**
     * Hook for session exit and reset (optional)
     *
     * @param data user data passed to fuse_session_new()
     * @param val exited status (1 - exited, 0 - not exited)
     */
    void (*exit) (void *data, int val);

    /**
     * Hook for querying the current exited status (optional)
     *
     * @param data user data passed to fuse_session_new()
     * @return 1 if exited, 0 if not exited
     */
    int (*exited) (void *data);

    /**
     * Hook for cleaning up the channel on destroy (optional)
     *
     * @param data user data passed to fuse_session_new()
     */
    void (*destroy) (void *data);
};

/**
 * Create a new session
 *
 * @param op session operations
 * @param data user data
 * @return new session object, or NULL on failure
 */
struct fuse_session *fuse_session_new(struct fuse_session_ops *op, void *data);

/**
 * Assign a channel to a session
 *
 * Note: currently only a single channel may be assigned.  This may
 * change in the future
 *
 * If a session is destroyed, the assigned channel is also destroyed
 *
 * @param se the session
 * @param ch the channel
 */
void fuse_session_add_chan(struct fuse_session *se, struct fuse_chan *ch);

/**
 * Remove a channel from a session
 *
 * If the channel is not assigned to a session, then this is a no-op
 *
 * @param ch the channel to remove
 */
void fuse_session_remove_chan(struct fuse_chan *ch);

/**
 * Iterate over the channels assigned to a session
 *
 * The iterating function needs to start with a NULL channel, and
 * after that needs to pass the previously returned channel to the
 * function.
 *
 * @param se the session
 * @param ch the previous channel, or NULL
 * @return the next channel, or NULL if no more channels exist
 */
struct fuse_chan *fuse_session_next_chan(struct fuse_session *se,
                                         struct fuse_chan *ch);

/**
 * Process a raw request
 *
 * @param se the session
 * @param buf buffer containing the raw request
 * @param len request length
 * @param ch channel on which the request was received
 */
void fuse_session_process(struct fuse_session *se, const char *buf, size_t len,
                          struct fuse_chan *ch);

/**
 * Destroy a session
 *
 * @param se the session
 */
void fuse_session_destroy(struct fuse_session *se);

/**
 * Exit a session
 *
 * @param se the session
 */
void fuse_session_exit(struct fuse_session *se);

/**
 * Reset the exited status of a session
 *
 * @param se the session
 */
void fuse_session_reset(struct fuse_session *se);

/**
 * Query the exited status of a session
 *
 * @param se the session
 * @return 1 if exited, 0 if not exited
 */
int fuse_session_exited(struct fuse_session *se);

/**
 * Enter a single threaded event loop
 *
 * @param se the session
 * @return 0 on success, -1 on error
 */
int fuse_session_loop(struct fuse_session *se);

/**
 * Enter a multi-threaded event loop
 *
 * @param se the session
 * @return 0 on success, -1 on error
 */
int fuse_session_loop_mt(struct fuse_session *se);

/* ----------------------------------------------------------- *
 * Channel interface                                           *
 * ----------------------------------------------------------- */

/**
 * Channel operations
 *
 * This is used in channel creation
 */
struct fuse_chan_ops {
    /**
     * Hook for receiving a raw request
     *
     * @param ch pointer to the channel
     * @param buf the buffer to store the request in
     * @param size the size of the buffer
     * @return the actual size of the raw request, or -1 on error
     */
    int (*receive)(struct fuse_chan **chp, char *buf, size_t size);

    /**
     * Hook for sending a raw reply
     *
     * A return value of -ENOENT means, that the request was
     * interrupted, and the reply was discarded
     *
     * @param ch the channel
     * @param iov vector of blocks
     * @param count the number of blocks in vector
     * @return zero on success, -errno on failure
     */
    int (*send)(struct fuse_chan *ch, const struct iovec iov[], size_t count);

    /**
     * Destroy the channel
     *
     * @param ch the channel
     */
    void (*destroy)(struct fuse_chan *ch);
};

/**
 * Create a new channel
 *
 * @param op channel operations
 * @param fd file descriptor of the channel
 * @param bufsize the minimal receive buffer size
 * @param data user data
 * @return the new channel object, or NULL on failure
 */
struct fuse_chan *fuse_chan_new(struct fuse_chan_ops *op, int fd,
                                size_t bufsize, void *data);

/**
 * Query the file descriptor of the channel
 *
 * @param ch the channel
 * @return the file descriptor passed to fuse_chan_new()
 */
int fuse_chan_fd(struct fuse_chan *ch);

/**
 * Query the minimal receive buffer size
 *
 * @param ch the channel
 * @return the buffer size passed to fuse_chan_new()
 */
size_t fuse_chan_bufsize(struct fuse_chan *ch);

/**
 * Query the user data
 *
 * @param ch the channel
 * @return the user data passed to fuse_chan_new()
 */
void *fuse_chan_data(struct fuse_chan *ch);

/**
 * Query the session to which this channel is assigned
 *
 * @param ch the channel
 * @return the session, or NULL if the channel is not assigned
 */
struct fuse_session *fuse_chan_session(struct fuse_chan *ch);

/**
 * Receive a raw request
 *
 * A return value of -ENODEV means, that the filesystem was unmounted
 *
 * @param ch pointer to the channel
 * @param buf the buffer to store the request in
 * @param size the size of the buffer
 * @return the actual size of the raw request, or -errno on error
 */
int fuse_chan_recv(struct fuse_chan **ch, char *buf, size_t size);

/**
 * Send a raw reply
 *
 * A return value of -ENOENT means, that the request was
 * interrupted, and the reply was discarded
 *
 * @param ch the channel
 * @param iov vector of blocks
 * @param count the number of blocks in vector
 * @return zero on success, -errno on failure
 */
int fuse_chan_send(struct fuse_chan *ch, const struct iovec iov[],
                   size_t count);

/**
 * Destroy a channel
 *
 * @param ch the channel
 */
void fuse_chan_destroy(struct fuse_chan *ch);

/* ----------------------------------------------------------- *
 * Compatibility stuff                                         *
 * ----------------------------------------------------------- */

#if FUSE_USE_VERSION < 26
#  include "fuse_lowlevel_compat.h"
#  define fuse_chan_ops fuse_chan_ops_compat24
#  define fuse_chan_new fuse_chan_new_compat24
#  if FUSE_USE_VERSION == 25
#    define fuse_lowlevel_ops fuse_lowlevel_ops_compat25
#    define fuse_lowlevel_new fuse_lowlevel_new_compat25
#  elif FUSE_USE_VERSION == 24
#    define fuse_lowlevel_ops fuse_lowlevel_ops_compat
#    define fuse_lowlevel_new fuse_lowlevel_new_compat
#    define fuse_file_info fuse_file_info_compat
#    define fuse_reply_statfs fuse_reply_statfs_compat
#    define fuse_reply_open fuse_reply_open_compat
#  else
#    error Compatibility with low-level API version < 24 not supported
#  endif
#endif

#ifdef __cplusplus
}
#endif

#endif /* _FUSE_LOWLEVEL_H_ */
