include/fuse.h

/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2007  Miklos Szeredi <miklos@szeredi.hu>

  This program can be distributed under the terms of the GNU LGPLv2.
  See the file LGPL2.txt.
*/

#ifndef FUSE_H_
#define FUSE_H_

/** @file
 *
 * This file defines the library interface of FUSE
 *
 * IMPORTANT: you should define FUSE_USE_VERSION before including this header.
 */

#include "fuse_common.h"

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

#ifdef __cplusplus
extern "C" {
#endif

/* ----------------------------------------------------------- *
 * Basic FUSE API					       *
 * ----------------------------------------------------------- */

/* Forward declaration */
struct statx;

/** Handle for a FUSE filesystem */
struct fuse;

/**
 * Readdir flags, passed to ->readdir()
 */
enum fuse_readdir_flags {
	/**
	 * "Plus" mode.
	 *
	 * The kernel wants to prefill the inode cache during readdir.  The
	 * filesystem may honour this by filling in the attributes and setting
	 * FUSE_FILL_DIR_FLAGS for the filler function.  The filesystem may also
	 * just ignore this flag completely.
	 */
	FUSE_READDIR_DEFAULTS = 0,
	FUSE_READDIR_PLUS = (1 << 0)
};

/**
 * Readdir flags, passed to fuse_fill_dir_t callback.
 */
enum fuse_fill_dir_flags {
	/**
	 * "Plus" mode: all file attributes are valid
	 *
	 * The attributes are used by the kernel to prefill the inode cache
	 * during a readdir.
	 *
	 * It is okay to set FUSE_FILL_DIR_PLUS if FUSE_READDIR_PLUS is not set
	 * and vice versa.
	 */
	FUSE_FILL_DIR_DEFAULTS = 0,
	FUSE_FILL_DIR_PLUS = (1 << 1)
};

/** Function to add an entry in a readdir() operation
 *
 * The *off* parameter can be any non-zero value that enables the
 * filesystem to identify the current point in the directory
 * stream. It does not need to be the actual physical position. A
 * value of zero is reserved to indicate that seeking in directories
 * is not supported.
 *
 * @param buf the buffer passed to the readdir() operation
 * @param name the file name of the directory entry
 * @param stbuf file attributes, can be NULL
 * @param off offset of the next entry or zero
 * @param flags fill flags
 * @return 1 if buffer is full, zero otherwise
 */
typedef int (*fuse_fill_dir_t) (void *buf, const char *name,
				const struct stat *stbuf, off_t off,
				enum fuse_fill_dir_flags flags);
/**
 * Configuration of the high-level API
 *
 * This structure is initialized from the arguments passed to
 * fuse_new(), and then passed to the file system's init() handler
 * which should ensure that the configuration is compatible with the
 * file system implementation.
 *
 * Note: this data structure is ABI sensitive, new options have to be
 * appended at the end of the structure
 */
struct fuse_config {
	/**
	 * If `set_gid` is non-zero, the st_gid attribute of each file
	 * is overwritten with the value of `gid`.
	 */
	int32_t set_gid;
	uint32_t gid;

	/**
	 * If `set_uid` is non-zero, the st_uid attribute of each file
	 * is overwritten with the value of `uid`.
	 */
	int32_t set_uid;
	uint32_t uid;

	/**
	 * If `set_mode` is non-zero, the any permissions bits set in
	 * `umask` are unset in the st_mode attribute of each file.
	 */
	int32_t set_mode;
	uint32_t umask;

	/**
	 * The timeout in seconds for which name lookups will be
	 * cached.
	 */
	double entry_timeout;

	/**
	 * The timeout in seconds for which a negative lookup will be
	 * cached. This means, that if file did not exist (lookup
	 * returned ENOENT), the lookup will only be redone after the
	 * timeout, and the file/directory will be assumed to not
	 * exist until then. A value of zero means that negative
	 * lookups are not cached.
	 */
	double negative_timeout;

	/**
	 * The timeout in seconds for which file/directory attributes
	 * (as returned by e.g. the `getattr` handler) are cached.
	 */
	double attr_timeout;

	/**
	 * Allow requests to be interrupted
	 */
	int32_t intr;

	/**
	 * Specify which signal number to send to the filesystem when
	 * a request is interrupted.  The default is hardcoded to
	 * USR1.
	 */
	int32_t intr_signal;

	/**
	 * Normally, FUSE assigns inodes to paths only for as long as
	 * the kernel is aware of them. With this option inodes are
	 * instead remembered for at least this many seconds.  This
	 * will require more memory, but may be necessary when using
	 * applications that make use of inode numbers.
	 *
	 * A number of -1 means that inodes will be remembered for the
	 * entire life-time of the file-system process.
	 */
	int32_t remember;

	/**
	 * The default behavior is that if an open file is deleted,
	 * the file is renamed to a hidden file (.fuse_hiddenXXX), and
	 * only removed when the file is finally released.  This
	 * relieves the filesystem implementation of having to deal
	 * with this problem. This option disables the hiding
	 * behavior, and files are removed immediately in an unlink
	 * operation (or in a rename operation which overwrites an
	 * existing file).
	 *
	 * It is recommended that you not use the hard_remove
	 * option. When hard_remove is set, the following libc
	 * functions fail on unlinked files (returning errno of
	 * ENOENT): read(2), write(2), fsync(2), close(2), f*xattr(2),
	 * ftruncate(2), fstat(2), fchmod(2), fchown(2)
	 */
	int32_t hard_remove;

	/**
	 * Honor the st_ino field in the functions getattr() and
	 * fill_dir(). This value is used to fill in the st_ino field
	 * in the stat(2), lstat(2), fstat(2) functions and the d_ino
	 * field in the readdir(2) function. The filesystem does not
	 * have to guarantee uniqueness, however some applications
	 * rely on this value being unique for the whole filesystem.
	 *
	 * Note that this does *not* affect the inode that libfuse
	 * and the kernel use internally (also called the "nodeid").
	 */
	int32_t use_ino;

	/**
	 * If use_ino option is not given, still try to fill in the
	 * d_ino field in readdir(2). If the name was previously
	 * looked up, and is still in the cache, the inode number
	 * found there will be used.  Otherwise it will be set to -1.
	 * If use_ino option is given, this option is ignored.
	 */
	int32_t readdir_ino;

	/**
	 * This option disables the use of page cache (file content cache)
	 * in the kernel for this filesystem. This has several affects:
	 *
	 * 1. Each read(2) or write(2) system call will initiate one
	 *    or more read or write operations, data will not be
	 *    cached in the kernel.
	 *
	 * 2. The return value of the read() and write() system calls
	 *    will correspond to the return values of the read and
	 *    write operations. This is useful for example if the
	 *    file size is not known in advance (before reading it).
	 *
	 * Internally, enabling this option causes fuse to set the
	 * `direct_io` field of `struct fuse_file_info` - overwriting
	 * any value that was put there by the file system.
	 */
	int32_t direct_io;

	/**
	 * This option disables flushing the cache of the file
	 * contents on every open(2).  This should only be enabled on
	 * filesystems where the file data is never changed
	 * externally (not through the mounted FUSE filesystem).  Thus
	 * it is not suitable for network filesystems and other
	 * intermediate filesystems.
	 *
	 * NOTE: if this option is not specified (and neither
	 * direct_io) data is still cached after the open(2), so a
	 * read(2) system call will not always initiate a read
	 * operation.
	 *
	 * Internally, enabling this option causes fuse to set the
	 * `keep_cache` field of `struct fuse_file_info` - overwriting
	 * any value that was put there by the file system.
	 */
	int32_t kernel_cache;

	/**
	 * This option is an alternative to `kernel_cache`. Instead of
	 * unconditionally keeping cached data, the cached data is
	 * invalidated on open(2) if if the modification time or the
	 * size of the file has changed since it was last opened.
	 */
	int32_t auto_cache;

	/*
	 * The timeout in seconds for which file attributes are cached
	 * for the purpose of checking if auto_cache should flush the
	 * file data on open.
	 */
	int32_t ac_attr_timeout_set;
	double ac_attr_timeout;

	/**
	 * If this option is given the file-system handlers for the
	 * following operations will not receive path information:
	 * read, write, flush, release, fallocate, fsync, readdir,
	 * releasedir, fsyncdir, lock, ioctl and poll.
	 *
	 * For the truncate, getattr, chmod, chown and utimens
	 * operations the path will be provided only if the struct
	 * fuse_file_info argument is NULL.
	 */
	int32_t nullpath_ok;

	/**
	 * These 3 options are used by libfuse internally and
	 * should not be touched.
	 */
	int32_t show_help;
	char *modules;
	int32_t debug;

	/**
	 * `fmask` and `dmask` function the same way as `umask`, but apply
	 * to files and directories separately. If non-zero, `fmask` and
	 * `dmask` take precedence over the `umask` setting.
	 */
	uint32_t fmask;
	uint32_t dmask;

	/**
	 * By default, fuse waits for all pending writes to complete
	 * and calls the FLUSH operation on close(2) of every fuse fd.
	 * With this option, wait and FLUSH are not done for read-only
	 * fuse fd, similar to the behavior of NFS/SMB clients.
	 */
	int32_t no_rofd_flush;

	/**
	 *  Allow parallel direct-io writes to operate on the same file.
	 *
	 *  FUSE implementations which do not handle parallel writes on
	 *  same file/region should NOT enable this option at all as it
	 *  might lead to data inconsistencies.
	 *
	 *  For the FUSE implementations which have their own mechanism
	 *  of cache/data integrity are beneficiaries of this setting as
	 *  it now open doors to parallel writes on the same file (without
	 *  enabling this setting, all direct writes on the same file are
	 *  serialized, resulting in huge data bandwidth loss).
	 */
	int32_t parallel_direct_writes;


	/**
	 * Reserved for future use.
	 */
	uint32_t flags;

	/**
	 * Reserved for future use.
	 */
	uint64_t reserved[48];
};


/**
 * The file system operations:
 *
 * Most of these should work very similarly to the well known UNIX
 * file system operations.  A major exception is that instead of
 * returning an error in 'errno', the operation should return the
 * negated error value (-errno) directly.
 *
 * All methods are optional, but some are essential for a useful
 * filesystem (e.g. getattr).  Open, flush, release, fsync, opendir,
 * releasedir, fsyncdir, access, create, truncate, lock, init and
 * destroy are special purpose methods, without which a full featured
 * filesystem can still be implemented.
 *
 * In general, all methods are expected to perform any necessary
 * permission checking. However, a filesystem may delegate this task
 * to the kernel by passing the `default_permissions` mount option to
 * `fuse_new()`. In this case, methods will only be called if
 * the kernel's permission check has succeeded.
 *
 * Almost all operations take a path which can be of any length.
 */
struct fuse_operations {
	/** Get file attributes.
	 *
	 * Similar to stat().  The 'st_dev' and 'st_blksize' fields are
	 * ignored. The 'st_ino' field is ignored except if the 'use_ino'
	 * mount option is given. In that case it is passed to userspace,
	 * but libfuse and the kernel will still assign a different
	 * inode for internal use (called the "nodeid").
	 *
	 * `fi` will always be NULL if the file is not currently open, but
	 * may also be NULL if the file is open.
	 */
	int (*getattr) (const char *, struct stat *, struct fuse_file_info *fi);

	/** Read the target of a symbolic link
	 *
	 * The buffer should be filled with a null terminated string.  The
	 * buffer size argument includes the space for the terminating
	 * null character.	If the linkname is too long to fit in the
	 * buffer, it should be truncated.	The return value should be 0
	 * for success.
	 */
	int (*readlink) (const char *, char *, size_t);

	/** Create a file node
	 *
	 * This is called for creation of all non-directory, non-symlink
	 * nodes.  If the filesystem defines a create() method, then for
	 * regular files that will be called instead.
	 */
	int (*mknod) (const char *, mode_t, dev_t);

	/** Create a directory
	 *
	 * Note that the mode argument may not have the type specification
	 * bits set, i.e. S_ISDIR(mode) can be false.  To obtain the
	 * correct directory type bits use  mode|S_IFDIR
	 * */
	int (*mkdir) (const char *, mode_t);

	/** Remove a file */
	int (*unlink) (const char *);

	/** Remove a directory */
	int (*rmdir) (const char *);

	/** Create a symbolic link */
	int (*symlink) (const char *, const char *);

	/** Rename a file
	 *
	 * *flags* may be `RENAME_EXCHANGE` or `RENAME_NOREPLACE`. If
	 * RENAME_NOREPLACE is specified, the filesystem must not
	 * overwrite *newname* if it exists and return an error
	 * instead. If `RENAME_EXCHANGE` is specified, the filesystem
	 * must atomically exchange the two files, i.e. both must
	 * exist and neither may be deleted.
	 */
	int (*rename) (const char *, const char *, unsigned int flags);

	/** Create a hard link to a file */
	int (*link) (const char *, const char *);

	/** Change the permission bits of a file
	 *
	 * `fi` will always be NULL if the file is not currently open, but
	 * may also be NULL if the file is open.
	 */
	int (*chmod) (const char *, mode_t, struct fuse_file_info *fi);

	/** Change the owner and group of a file
	 *
	 * `fi` will always be NULL if the file is not currently open, but
	 * may also be NULL if the file is open.
	 *
	 * Unless FUSE_CAP_HANDLE_KILLPRIV is disabled, this method is
	 * expected to reset the setuid and setgid bits.
	 */
	int (*chown) (const char *, uid_t, gid_t, struct fuse_file_info *fi);

	/** Change the size of a file
	 *
	 * `fi` will always be NULL if the file is not currently open, but
	 * may also be NULL if the file is open.
	 *
	 * Unless FUSE_CAP_HANDLE_KILLPRIV is disabled, this method is
	 * expected to reset the setuid and setgid bits.
	 */
	int (*truncate) (const char *, off_t, struct fuse_file_info *fi);

	/** Open a file
	 *
	 * Open flags are available in fi->flags. The following rules
	 * apply.
	 *
	 *  - Creation (O_CREAT, O_EXCL, O_NOCTTY) flags will be
	 *    filtered out / handled by the kernel.
	 *
	 *  - Access modes (O_RDONLY, O_WRONLY, O_RDWR, O_EXEC, O_SEARCH)
	 *    should be used by the filesystem to check if the operation is
	 *    permitted.  If the ``-o default_permissions`` mount option is
	 *    given, this check is already done by the kernel before calling
	 *    open() and may thus be omitted by the filesystem.
	 *
	 *  - When writeback caching is enabled, the kernel may send
	 *    read requests even for files opened with O_WRONLY. The
	 *    filesystem should be prepared to handle this.
	 *
	 *  - When writeback caching is disabled, the filesystem is
	 *    expected to properly handle the O_APPEND flag and ensure
	 *    that each write is appending to the end of the file.
	 *
	 *  - When writeback caching is enabled, the kernel will
	 *    handle O_APPEND. However, unless all changes to the file
	 *    come through the kernel this will not work reliably. The
	 *    filesystem should thus either ignore the O_APPEND flag
	 *    (and let the kernel handle it), or return an error
	 *    (indicating that reliably O_APPEND is not available).
	 *
	 * 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.
	 *
	 * If this request is answered with an error code of ENOSYS
	 * and FUSE_CAP_NO_OPEN_SUPPORT is set in
	 * `fuse_conn_info.capable`, this is treated as success and
	 * future calls to open will also succeed without being sent
	 * to the filesystem process.
	 *
	 */
	int (*open) (const char *, struct fuse_file_info *);

	/** Read data from an open file
	 *
	 * Read should return 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
	 * 'direct_io' mount option is specified, in which case the return
	 * value of the read system call will reflect the return value of
	 * this operation.
	 */
	int (*read) (const char *, char *, size_t, off_t,
		     struct fuse_file_info *);

	/** Write data to an open file
	 *
	 * Write should return exactly the number of bytes requested
	 * except on error.	 An exception to this is when the 'direct_io'
	 * mount option is specified (see read operation).
	 *
	 * Unless FUSE_CAP_HANDLE_KILLPRIV is disabled, this method is
	 * expected to reset the setuid and setgid bits.
	 */
	int (*write) (const char *, const char *, size_t, off_t,
		      struct fuse_file_info *);

	/** Get file system statistics
	 *
	 * The 'f_favail', 'f_fsid' and 'f_flag' fields are ignored
	 */
	int (*statfs) (const char *, struct statvfs *);

	/** Possibly flush cached data
	 *
	 * BIG NOTE: This is not equivalent to fsync().  It's not a
	 * request to sync dirty data.
	 *
	 * Flush is called on each close() of a file descriptor, as opposed to
	 * release which is called on the close of the last file descriptor for
	 * a file.  Under Linux, errors returned by flush() will be passed to
	 * userspace as errors from close(), so flush() is a good place to write
	 * back any cached dirty data. However, many applications ignore errors
	 * on close(), and on non-Linux systems, close() may succeed even if flush()
	 * returns an error. For these reasons, filesystems should not assume
	 * that errors returned by flush will ever be noticed or even
	 * delivered.
	 *
	 * NOTE: The flush() method may be called more than once for each
	 * open().  This happens if more than one file descriptor refers to an
	 * open file handle, e.g. due to dup(), dup2() or fork() calls.  It is
	 * not possible to determine if a flush is final, so each flush should
	 * be treated equally.  Multiple write-flush sequences are relatively
	 * rare, so this shouldn't be a problem.
	 *
	 * Filesystems shouldn't assume that flush will be called at any
	 * particular point.  It may be called more times than expected, or not
	 * at all.
	 *
	 * [close]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/close.html
	 */
	int (*flush) (const char *, struct fuse_file_info *);

	/** 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
	 * with the same flags and file handle.  It is possible to
	 * have a file opened more than once, in which case only the last
	 * release will mean, that no more reads/writes will happen on the
	 * file.  The return value of release is ignored.
	 */
	int (*release) (const char *, struct fuse_file_info *);

	/** Synchronize file contents
	 *
	 * If the datasync parameter is non-zero, then only the user data
	 * should be flushed, not the meta data.
	 */
	int (*fsync) (const char *, int, struct fuse_file_info *);

	/** Set extended attributes */
	int (*setxattr) (const char *, const char *, const char *, size_t, int);

	/** Get extended attributes */
	int (*getxattr) (const char *, const char *, char *, size_t);

	/** List extended attributes */
	int (*listxattr) (const char *, char *, size_t);

	/** Remove extended attributes */
	int (*removexattr) (const char *, const char *);

	/** Open directory
	 *
	 * Unless the 'default_permissions' mount option is given,
	 * this method should check if opendir is permitted for this
	 * directory. Optionally opendir may also return an arbitrary
	 * filehandle in the fuse_file_info structure, which will be
	 * passed to readdir, releasedir and fsyncdir.
	 */
	int (*opendir) (const char *, struct fuse_file_info *);

	/** Read directory
	 *
	 * The filesystem may choose between two modes of operation:
	 *
	 * 1) The readdir implementation ignores the offset parameter, and
	 * passes zero to the filler function's offset.  The filler
	 * function will not return '1' (unless an error happens), so the
	 * whole directory is read in a single readdir operation.
	 *
	 * 2) The readdir implementation keeps track of the offsets of the
	 * directory entries.  It uses the offset parameter and always
	 * passes non-zero offset to the filler function.  When the buffer
	 * is full (or an error happens) the filler function will return
	 * '1'.
	 *
	 * When FUSE_READDIR_PLUS is not set, only some parameters of the
	 * fill function (the fuse_fill_dir_t parameter) are actually used:
	 * The file type (which is part of stat::st_mode) is used. And if
	 * fuse_config::use_ino is set, the inode (stat::st_ino) is also
	 * used. The other fields are ignored when FUSE_READDIR_PLUS is not
	 * set.
	 */
	int (*readdir) (const char *, void *, fuse_fill_dir_t, off_t,
			struct fuse_file_info *, enum fuse_readdir_flags);

	/** Release directory
	 *
	 * If the directory has been removed after the call to opendir, the
	 * path parameter will be NULL.
	 */
	int (*releasedir) (const char *, struct fuse_file_info *);

	/** Synchronize directory contents
	 *
	 * If the directory has been removed after the call to opendir, the
	 * path parameter will be NULL.
	 *
	 * If the datasync parameter is non-zero, then only the user data
	 * should be flushed, not the meta data
	 */
	int (*fsyncdir) (const char *, int, struct fuse_file_info *);

	/**
	 * Initialize filesystem
	 *
	 * The return value will passed in the `private_data` field of
	 * `struct fuse_context` to all file operations, and as a
	 * parameter to the destroy() method. It overrides the initial
	 * value provided to fuse_main() / fuse_new().
	 */
	void *(*init) (struct fuse_conn_info *conn,
		       struct fuse_config *cfg);

	/**
	 * Clean up filesystem
	 *
	 * Called on filesystem exit.
	 */
	void (*destroy) (void *private_data);

	/**
	 * 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
	 */
	int (*access) (const char *, int);

	/**
	 * Create and open a file
	 *
	 * If the file does not exist, first create it with the specified
	 * mode, and then open it.
	 *
	 * 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.
	 */
	int (*create) (const char *, mode_t, struct fuse_file_info *);

	/**
	 * Perform POSIX file locking operation
	 *
	 * The cmd argument will be either F_GETLK, F_SETLK or F_SETLKW.
	 *
	 * For the meaning of fields in 'struct flock' see the man page
	 * for fcntl(2).  The l_whence field will always be set to
	 * SEEK_SET.
	 *
	 * For checking lock ownership, the 'fuse_file_info->owner'
	 * argument must be used.
	 *
	 * For F_GETLK operation, the library will first check currently
	 * held locks, and if a conflicting lock is found it will return
	 * information without calling this method.	 This ensures, that
	 * for local locks the l_pid field is correctly filled in.	The
	 * results may not be accurate in case of race conditions and in
	 * the presence of hard links, but it's unlikely that an
	 * application would rely on accurate GETLK results in these
	 * cases.  If a conflicting lock is not found, this method will be
	 * called, and the filesystem may fill out l_pid by a meaningful
	 * value, or it may leave this field zero.
	 *
	 * For F_SETLK and F_SETLKW the l_pid field will be set to the pid
	 * of the process performing the locking operation.
	 *
	 * Note: if this method is not implemented, the kernel will still
	 * allow file locking to work locally.  Hence it is only
	 * interesting for network filesystems and similar.
	 */
	int (*lock) (const char *, struct fuse_file_info *, int cmd,
		     struct flock *);

	/**
	 * Change the access and modification times of a file with
	 * nanosecond resolution
	 *
	 * This supersedes the old utime() interface.  New applications
	 * should use this.
	 *
	 * `fi` will always be NULL if the file is not currently open, but
	 * may also be NULL if the file is open.
	 *
	 * See the utimensat(2) man page for details.
	 */
	 int (*utimens) (const char *, const struct timespec tv[2],
			 struct fuse_file_info *fi);

	/**
	 * 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
	 */
	int (*bmap) (const char *, size_t blocksize, uint64_t *idx);

#if FUSE_USE_VERSION < 35
	int (*ioctl) (const char *, int cmd, void *arg,
		      struct fuse_file_info *, unsigned int flags, void *data);
#else
	/**
	 * Ioctl
	 *
	 * flags will have FUSE_IOCTL_COMPAT set for 32bit ioctls in
	 * 64bit environment.  The size and direction of data is
	 * determined by _IOC_*() decoding of cmd.  For _IOC_NONE,
	 * data will be NULL, for _IOC_WRITE data is out area, for
	 * _IOC_READ in area and if both are set in/out area.  In all
	 * non-NULL cases, the area is of _IOC_SIZE(cmd) bytes.
	 *
	 * If flags has FUSE_IOCTL_DIR then the fuse_file_info refers to a
	 * directory file handle.
	 *
	 * Note : the unsigned long request submitted by the application
	 * is truncated to 32 bits.
	 */
	int (*ioctl) (const char *, unsigned int cmd, void *arg,
		      struct fuse_file_info *, unsigned int flags, void *data);
#endif

	/**
	 * Poll for IO readiness events
	 *
	 * Note: If ph is non-NULL, the client should notify
	 * when IO readiness events occur by calling
	 * fuse_notify_poll() with the specified ph.
	 *
	 * Regardless of the number of times poll with a non-NULL ph
	 * is received, single notification is enough to clear all.
	 * Notifying more times incurs overhead but doesn't harm
	 * correctness.
	 *
	 * The callee is responsible for destroying ph with
	 * fuse_pollhandle_destroy() when no longer in use.
	 */
	int (*poll) (const char *, struct fuse_file_info *,
		     struct fuse_pollhandle *ph, unsigned *reventsp);

	/** Write contents of buffer to an open file
	 *
	 * Similar to the write() method, but data is supplied in a
	 * generic buffer.  Use fuse_buf_copy() to transfer data to
	 * the destination.
	 *
	 * Unless FUSE_CAP_HANDLE_KILLPRIV is disabled, this method is
	 * expected to reset the setuid and setgid bits.
	 */
	int (*write_buf) (const char *, struct fuse_bufvec *buf, off_t off,
			  struct fuse_file_info *);

	/** Store data from an open file in a buffer
	 *
	 * Similar to the read() method, but data is stored and
	 * returned in a generic buffer.
	 *
	 * No actual copying of data has to take place, the source
	 * file descriptor may simply be stored in the buffer for
	 * later data transfer.
	 *
	 * The buffer must be allocated dynamically and stored at the
	 * location pointed to by bufp.  If the buffer contains memory
	 * regions, they too must be allocated using malloc().  The
	 * allocated memory will be freed by the caller.
	 */
	int (*read_buf) (const char *, struct fuse_bufvec **bufp,
			 size_t size, off_t off, struct fuse_file_info *);
	/**
	 * Perform BSD file locking operation
	 *
	 * The op argument will be either LOCK_SH, LOCK_EX or LOCK_UN
	 *
	 * Nonblocking requests will be indicated by ORing LOCK_NB to
	 * the above operations
	 *
	 * For more information see the flock(2) manual page.
	 *
	 * Additionally fi->owner will be set to a value unique to
	 * this open file.  This same value will be supplied to
	 * ->release() when the file is released.
	 *
	 * Note: if this method is not implemented, the kernel will still
	 * allow file locking to work locally.  Hence it is only
	 * interesting for network filesystems and similar.
	 */
	int (*flock) (const char *, struct fuse_file_info *, int op);

	/**
	 * Allocates space for an open file
	 *
	 * This function ensures that required space is allocated for specified
	 * file.  If this function returns success then any subsequent write
	 * request to specified range is guaranteed not to fail because of lack
	 * of space on the file system media.
	 */
	int (*fallocate) (const char *, int, off_t, off_t,
			  struct fuse_file_info *);

	/**
	 * Copy a range of data from one file to another
	 *
	 * Performs an optimized copy between two file descriptors without the
	 * additional cost of transferring data through the FUSE kernel module
	 * to user space (glibc) and then back into the FUSE filesystem again.
	 *
	 * In case this method is not implemented, applications are expected to
	 * fall back to a regular file copy.   (Some glibc versions did this
	 * emulation automatically, but the emulation has been removed from all
	 * glibc release branches.)
	 */
	ssize_t (*copy_file_range) (const char *path_in,
				    struct fuse_file_info *fi_in,
				    off_t offset_in, const char *path_out,
				    struct fuse_file_info *fi_out,
				    off_t offset_out, size_t size, int flags);

	/**
	 * Find next data or hole after the specified offset
	 */
	off_t (*lseek) (const char *, off_t off, int whence, struct fuse_file_info *);

#ifdef HAVE_STATX
	/**
	 * Get extended file attributes.
	 *
	 * fi may be NULL.
	 *
	 * If path is NULL, then the AT_EMPTY_PATH bit in flags will be
	 * already set.
	 */
	int (*statx)(const char *path, int flags, int mask, struct statx *stxbuf,
		     struct fuse_file_info *fi);
#endif
};

/** Extra context that may be needed by some filesystems
 *
 * The uid, gid and pid fields are not filled in case of a writepage
 * operation.
 */
struct fuse_context {
	/** Pointer to the fuse object */
	struct fuse *fuse;

	/** User ID of the calling process */
	uid_t uid;

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

	/** Process ID of the calling thread */
	pid_t pid;

	/** Private filesystem data */
	void *private_data;

	/** Umask of the calling process */
	mode_t umask;
};

/**
 * The real main function
 *
 * Do not call this directly, use fuse_main()
 */
int fuse_main_real_versioned(int argc, char *argv[],
			     const struct fuse_operations *op, size_t op_size,
			     struct libfuse_version *version, void *user_data);
static inline int fuse_main_real(int argc, char *argv[],
				 const struct fuse_operations *op,
				 size_t op_size, void *user_data)
{
	struct libfuse_version version = { .major = FUSE_MAJOR_VERSION,
					   .minor = FUSE_MINOR_VERSION,
					   .hotfix = FUSE_HOTFIX_VERSION,
					   .padding = 0 };

	fuse_log(FUSE_LOG_ERR,
		 "%s is a libfuse internal function, please use fuse_main()\n",
		 __func__);

	return fuse_main_real_versioned(argc, argv, op, op_size, &version,
					user_data);
}

/**
 * Main function of FUSE.
 *
 * This is for the lazy.  This is all that has to be called from the
 * main() function.
 *
 * This function does the following:
 *   - parses command line options, and handles --help and
 *     --version
 *   - installs signal handlers for INT, HUP, TERM and PIPE
 *   - registers an exit handler to unmount the filesystem on program exit
 *   - creates a fuse handle
 *   - registers the operations
 *   - calls either the single-threaded or the multi-threaded event loop
 *
 * Most file systems will have to parse some file-system specific
 * arguments before calling this function. It is recommended to do
 * this with fuse_opt_parse() and a processing function that passes
 * through any unknown options (this can also be achieved by just
 * passing NULL as the processing function). That way, the remaining
 * options can be passed directly to fuse_main().
 *
 * fuse_main() accepts all options that can be passed to
 * fuse_parse_cmdline(), fuse_new(), or fuse_session_new().
 *
 * Option parsing skips argv[0], which is assumed to contain the
 * program name. This element must always be present and is used to
 * construct a basic ``usage: `` message for the --help
 * output. argv[0] may also be set to the empty string. In this case
 * the usage message is suppressed. This can be used by file systems
 * to print their own usage line first. See hello.c for an example of
 * how to do this.
 *
 * Note: this is currently implemented as a macro.
 *
 * The following error codes may be returned from fuse_main():
 *   1: Invalid option arguments
 *   2: No mount point specified
 *   3: FUSE setup failed
 *   4: Mounting failed
 *   5: Failed to daemonize (detach from session)
 *   6: Failed to set up signal handlers
 *   7: An error occurred during the life of the file system
 *
 * @param argc the argument counter passed to the main() function
 * @param argv the argument vector passed to the main() function
 * @param op the file system operation
 * @param private_data Initial value for the `private_data`
 *            field of `struct fuse_context`. May be overridden by the
 *            `struct fuse_operations.init` handler.
 * @return 0 on success, nonzero on failure
 *
 * Example usage, see hello.c
 */
static inline int fuse_main_fn(int argc, char *argv[],
			       const struct fuse_operations *op,
			       void *user_data)
{
	struct libfuse_version version = {
		.major  = FUSE_MAJOR_VERSION,
		.minor  = FUSE_MINOR_VERSION,
		.hotfix = FUSE_HOTFIX_VERSION,
		.padding = 0
	};

	return fuse_main_real_versioned(argc, argv, op, sizeof(*(op)), &version,
					user_data);
}
#define fuse_main(argc, argv, op, user_data) \
	fuse_main_fn(argc, argv, op, user_data)

/* ----------------------------------------------------------- *
 * More detailed API					       *
 * ----------------------------------------------------------- */

/**
 * Print available options (high- and low-level) to stdout.  This is
 * not an exhaustive list, but includes only those options that may be
 * of interest to an end-user of a file system.
 *
 * The function looks at the argument vector only to determine if
 * there are additional modules to be loaded (module=foo option),
 * and attempts to call their help functions as well.
 *
 * @param args the argument vector.
 */
void fuse_lib_help(struct fuse_args *args);

/* Do not call this directly, use fuse_new() instead */
struct fuse *_fuse_new_30(struct fuse_args *args,
			  const struct fuse_operations *op, size_t op_size,
			  struct libfuse_version *version, void *user_data);
struct fuse *_fuse_new_31(struct fuse_args *args,
			  const struct fuse_operations *op, size_t op_size,
			  struct libfuse_version *version, void *user_data);

/**
 * Create a new FUSE filesystem.
 *
 * This function accepts most file-system independent mount options
 * (like context, nodev, ro - see mount(8)), as well as the
 * FUSE-specific mount options from mount.fuse(8).
 *
 * If the --help option is specified, the function writes a help text
 * to stdout and returns NULL.
 *
 * Option parsing skips argv[0], which is assumed to contain the
 * program name. This element must always be present and is used to
 * construct a basic ``usage: `` message for the --help output. If
 * argv[0] is set to the empty string, no usage message is included in
 * the --help output.
 *
 * If an unknown option is passed in, an error message is written to
 * stderr and the function returns NULL.
 *
 * @param args argument vector
 * @param op the filesystem operations
 * @param op_size the size of the fuse_operations structure
 * @param private_data Initial value for the `private_data`
 *            field of `struct fuse_context`. May be overridden by the
 *            `struct fuse_operations.init` handler.
 * @return the created FUSE handle
 */
#if FUSE_USE_VERSION == 30
static inline struct fuse *fuse_new_fn(struct fuse_args *args,
				       const struct fuse_operations *op,
				       size_t op_size, void *user_data)
{
	struct libfuse_version version = {
		.major = FUSE_MAJOR_VERSION,
		.minor = FUSE_MINOR_VERSION,
		.hotfix = FUSE_HOTFIX_VERSION,
		.padding = 0
	};

	return _fuse_new_30(args, op, op_size, &version, user_data);
}
#else /* FUSE_USE_VERSION */
static inline struct fuse *fuse_new_fn(struct fuse_args *args,
				       const struct fuse_operations *op,
				       size_t op_size, void *user_data)
{
	struct libfuse_version version = {
		.major = FUSE_MAJOR_VERSION,
		.minor = FUSE_MINOR_VERSION,
		.hotfix = FUSE_HOTFIX_VERSION,
		.padding = 0
	};

	return _fuse_new_31(args, op, op_size, &version, user_data);
}
#endif
#define fuse_new(args, op, size, data) fuse_new_fn(args, op, size, data)

/**
 * Mount a FUSE file system.
 *
 * @param mountpoint the mount point path
 * @param f the FUSE handle
 *
 * @return 0 on success, -1 on failure.
 **/
int fuse_mount(struct fuse *f, const char *mountpoint);

/**
 * Unmount a FUSE file system.
 *
 * See fuse_session_unmount() for additional information.
 *
 * @param f the FUSE handle
 **/
void fuse_unmount(struct fuse *f);

/**
 * Destroy the FUSE handle.
 *
 * NOTE: This function does not unmount the filesystem.	 If this is
 * needed, call fuse_unmount() before calling this function.
 *
 * @param f the FUSE handle
 */
void fuse_destroy(struct fuse *f);

/**
 * FUSE event loop.
 *
 * Requests from the kernel are processed, and the appropriate
 * operations are called.
 *
 * For a description of the return value and the conditions when the
 * event loop exits, refer to the documentation of
 * fuse_session_loop().
 *
 * @param f the FUSE handle
 * @return see fuse_session_loop()
 *
 * See also: fuse_loop_mt()
 */
int fuse_loop(struct fuse *f);

/**
 * Flag session as terminated
 *
 * This function will cause any running event loops to exit on
 * the next opportunity.
 *
 * @param f the FUSE handle
 */
void fuse_exit(struct fuse *f);

#if FUSE_USE_VERSION < 32
int fuse_loop_mt_31(struct fuse *f, int clone_fd);
#define fuse_loop_mt(f, clone_fd) fuse_loop_mt_31(f, clone_fd)
#elif FUSE_USE_VERSION < FUSE_MAKE_VERSION(3, 12)
int fuse_loop_mt_32(struct fuse *f, struct fuse_loop_config *config);
#define fuse_loop_mt(f, config) fuse_loop_mt_32(f, config)
#else
/**
 * FUSE event loop with multiple threads
 *
 * Requests from the kernel are processed, and the appropriate
 * operations are called.  Request are processed in parallel by
 * distributing them between multiple threads.
 *
 * For a description of the return value and the conditions when the
 * event loop exits, refer to the documentation of
 * fuse_session_loop().
 *
 * Note: using fuse_loop() instead of fuse_loop_mt() means you are running in
 * single-threaded mode, and that you will not have to worry about reentrancy,
 * though you will have to worry about recursive lookups. In single-threaded
 * mode, FUSE will wait for one callback to return before calling another.
 *
 * Enabling multiple threads, by using fuse_loop_mt(), will cause FUSE to make
 * multiple simultaneous calls into the various callback functions given by your
 * fuse_operations record.
 *
 * If you are using multiple threads, you can enjoy all the parallel execution
 * and interactive response benefits of threads, and you get to enjoy all the
 * benefits of race conditions and locking bugs, too. Ensure that any code used
 * in the callback function of fuse_operations is also thread-safe.
 *
 * @param f the FUSE handle
 * @param config loop configuration, may be NULL and defaults will be used then
 * @return see fuse_session_loop()
 *
 * See also: fuse_loop()
 */
#if (defined(LIBFUSE_BUILT_WITH_VERSIONED_SYMBOLS))
int fuse_loop_mt(struct fuse *f, struct fuse_loop_config *config);
#else
#define fuse_loop_mt(f, config) fuse_loop_mt_312(f, config)
#endif /* LIBFUSE_BUILT_WITH_VERSIONED_SYMBOLS */
#endif


/**
 * Get the current context
 *
 * The context is only valid for the duration of a filesystem
 * operation, and thus must not be stored and used later.
 *
 * @return the context
 */
struct fuse_context *fuse_get_context(void);

/**
 * Get the current supplementary group IDs for the current request
 *
 * Similar to the getgroups(2) system call, except the return value is
 * always the total number of group IDs, even if it is larger than the
 * specified size.
 *
 * The current fuse kernel module in linux (as of 2.6.30) doesn't pass
 * the group list to userspace, hence this function needs to parse
 * "/proc/$TID/task/$TID/status" to get the group IDs.
 *
 * This feature may not be supported on all operating systems.  In
 * such a case this function will return -ENOSYS.
 *
 * @param size size of given array
 * @param list array of group IDs to be filled in
 * @return the total number of supplementary group IDs or -errno on failure
 */
int fuse_getgroups(int size, gid_t list[]);

/**
 * Check if the current request has already been interrupted
 *
 * @return 1 if the request has been interrupted, 0 otherwise
 */
int fuse_interrupted(void);

/**
 * Invalidates cache for the given path.
 *
 * This calls fuse_lowlevel_notify_inval_inode internally.
 *
 * @return 0 on successful invalidation, negative error value otherwise.
 *         This routine may return -ENOENT to indicate that there was
 *         no entry to be invalidated, e.g., because the path has not
 *         been seen before or has been forgotten; this should not be
 *         considered to be an error.
 */
int fuse_invalidate_path(struct fuse *f, const char *path);

/**
 * Start the cleanup thread when using option "remember".
 *
 * This is done automatically by fuse_loop_mt()
 * @param fuse struct fuse pointer for fuse instance
 * @return 0 on success and -1 on error
 */
int fuse_start_cleanup_thread(struct fuse *fuse);

/**
 * Stop the cleanup thread when using option "remember".
 *
 * This is done automatically by fuse_loop_mt()
 * @param fuse struct fuse pointer for fuse instance
 */
void fuse_stop_cleanup_thread(struct fuse *fuse);

/**
 * Iterate over cache removing stale entries
 * use in conjunction with "-oremember"
 *
 * NOTE: This is already done for the standard sessions
 *
 * @param fuse struct fuse pointer for fuse instance
 * @return the number of seconds until the next cleanup
 */
int fuse_clean_cache(struct fuse *fuse);

/*
 * Stacking API
 */

/**
 * Fuse filesystem object
 *
 * This is opaque object represents a filesystem layer
 */
struct fuse_fs;

/*
 * These functions call the relevant filesystem operation, and return
 * the result.
 *
 * If the operation is not defined, they return -ENOSYS, with the
 * exception of fuse_fs_open, fuse_fs_release, fuse_fs_opendir,
 * fuse_fs_releasedir and fuse_fs_statfs, which return 0.
 */

int fuse_fs_getattr(struct fuse_fs *fs, const char *path, struct stat *buf,
		    struct fuse_file_info *fi);
int fuse_fs_rename(struct fuse_fs *fs, const char *oldpath,
		   const char *newpath, unsigned int flags);
int fuse_fs_unlink(struct fuse_fs *fs, const char *path);
int fuse_fs_rmdir(struct fuse_fs *fs, const char *path);
int fuse_fs_symlink(struct fuse_fs *fs, const char *linkname,
		    const char *path);
int fuse_fs_link(struct fuse_fs *fs, const char *oldpath, const char *newpath);
int fuse_fs_release(struct fuse_fs *fs,	 const char *path,
		    struct fuse_file_info *fi);
int fuse_fs_open(struct fuse_fs *fs, const char *path,
		 struct fuse_file_info *fi);
int fuse_fs_read(struct fuse_fs *fs, const char *path, char *buf, size_t size,
		 off_t off, struct fuse_file_info *fi);
int fuse_fs_read_buf(struct fuse_fs *fs, const char *path,
		     struct fuse_bufvec **bufp, size_t size, off_t off,
		     struct fuse_file_info *fi);
int fuse_fs_write(struct fuse_fs *fs, const char *path, const char *buf,
		  size_t size, off_t off, struct fuse_file_info *fi);
int fuse_fs_write_buf(struct fuse_fs *fs, const char *path,
		      struct fuse_bufvec *buf, off_t off,
		      struct fuse_file_info *fi);
int fuse_fs_fsync(struct fuse_fs *fs, const char *path, int datasync,
		  struct fuse_file_info *fi);
int fuse_fs_flush(struct fuse_fs *fs, const char *path,
		  struct fuse_file_info *fi);
int fuse_fs_statfs(struct fuse_fs *fs, const char *path, struct statvfs *buf);
int fuse_fs_opendir(struct fuse_fs *fs, const char *path,
		    struct fuse_file_info *fi);
int fuse_fs_readdir(struct fuse_fs *fs, const char *path, void *buf,
		    fuse_fill_dir_t filler, off_t off,
		    struct fuse_file_info *fi, enum fuse_readdir_flags flags);
int fuse_fs_fsyncdir(struct fuse_fs *fs, const char *path, int datasync,
		     struct fuse_file_info *fi);
int fuse_fs_releasedir(struct fuse_fs *fs, const char *path,
		       struct fuse_file_info *fi);
int fuse_fs_create(struct fuse_fs *fs, const char *path, mode_t mode,
		   struct fuse_file_info *fi);
int fuse_fs_lock(struct fuse_fs *fs, const char *path,
		 struct fuse_file_info *fi, int cmd, struct flock *lock);
int fuse_fs_flock(struct fuse_fs *fs, const char *path,
		  struct fuse_file_info *fi, int op);
int fuse_fs_chmod(struct fuse_fs *fs, const char *path, mode_t mode,
		  struct fuse_file_info *fi);
int fuse_fs_chown(struct fuse_fs *fs, const char *path, uid_t uid, gid_t gid,
		  struct fuse_file_info *fi);
int fuse_fs_truncate(struct fuse_fs *fs, const char *path, off_t size,
		     struct fuse_file_info *fi);
int fuse_fs_utimens(struct fuse_fs *fs, const char *path,
		    const struct timespec tv[2], struct fuse_file_info *fi);
int fuse_fs_access(struct fuse_fs *fs, const char *path, int mask);
int fuse_fs_readlink(struct fuse_fs *fs, const char *path, char *buf,
		     size_t len);
int fuse_fs_mknod(struct fuse_fs *fs, const char *path, mode_t mode,
		  dev_t rdev);
int fuse_fs_mkdir(struct fuse_fs *fs, const char *path, mode_t mode);
int fuse_fs_setxattr(struct fuse_fs *fs, const char *path, const char *name,
		     const char *value, size_t size, int flags);
int fuse_fs_getxattr(struct fuse_fs *fs, const char *path, const char *name,
		     char *value, size_t size);
int fuse_fs_listxattr(struct fuse_fs *fs, const char *path, char *list,
		      size_t size);
int fuse_fs_removexattr(struct fuse_fs *fs, const char *path,
			const char *name);
int fuse_fs_bmap(struct fuse_fs *fs, const char *path, size_t blocksize,
		 uint64_t *idx);
#if FUSE_USE_VERSION < 35
int fuse_fs_ioctl(struct fuse_fs *fs, const char *path, int cmd,
		  void *arg, struct fuse_file_info *fi, unsigned int flags,
		  void *data);
#else
int fuse_fs_ioctl(struct fuse_fs *fs, const char *path, unsigned int cmd,
		  void *arg, struct fuse_file_info *fi, unsigned int flags,
		  void *data);
#endif
int fuse_fs_poll(struct fuse_fs *fs, const char *path,
		 struct fuse_file_info *fi, struct fuse_pollhandle *ph,
		 unsigned *reventsp);
int fuse_fs_fallocate(struct fuse_fs *fs, const char *path, int mode,
		 off_t offset, off_t length, struct fuse_file_info *fi);
ssize_t fuse_fs_copy_file_range(struct fuse_fs *fs, const char *path_in,
				struct fuse_file_info *fi_in, off_t off_in,
				const char *path_out,
				struct fuse_file_info *fi_out, off_t off_out,
				size_t len, int flags);
off_t fuse_fs_lseek(struct fuse_fs *fs, const char *path, off_t off, int whence,
		    struct fuse_file_info *fi);
int fuse_fs_statx(struct fuse_fs *fs, const char *path, int flags, int mask,
		  struct statx *stxbuf, struct fuse_file_info *fi);
void fuse_fs_init(struct fuse_fs *fs, struct fuse_conn_info *conn,
		struct fuse_config *cfg);
void fuse_fs_destroy(struct fuse_fs *fs);

int fuse_notify_poll(struct fuse_pollhandle *ph);

/**
 * Create a new fuse filesystem object
 *
 * This is usually called from the factory of a fuse module to create
 * a new instance of a filesystem.
 *
 * @param op the filesystem operations
 * @param op_size the size of the fuse_operations structure
 * @param private_data Initial value for the `private_data`
 *            field of `struct fuse_context`. May be overridden by the
 *            `struct fuse_operations.init` handler.
 * @return a new filesystem object
 */
struct fuse_fs *fuse_fs_new(const struct fuse_operations *op, size_t op_size,
			    void *private_data);

/**
 * Factory for creating filesystem objects
 *
 * The function may use and remove options from 'args' that belong
 * to this module.
 *
 * For now the 'fs' vector always contains exactly one filesystem.
 * This is the filesystem which will be below the newly created
 * filesystem in the stack.
 *
 * @param args the command line arguments
 * @param fs NULL terminated filesystem object vector
 * @return the new filesystem object
 */
typedef struct fuse_fs *(*fuse_module_factory_t)(struct fuse_args *args,
						 struct fuse_fs *fs[]);
/**
 * Register filesystem module
 *
 * If the "-omodules=*name*_:..." option is present, filesystem
 * objects are created and pushed onto the stack with the *factory_*
 * function.
 *
 * @param name_ the name of this filesystem module
 * @param factory_ the factory function for this filesystem module
 */
#define FUSE_REGISTER_MODULE(name_, factory_) \
	fuse_module_factory_t fuse_module_ ## name_ ## _factory = factory_

/** Get session from fuse object */
struct fuse_session *fuse_get_session(struct fuse *f);

/**
 * Open a FUSE file descriptor and set up the mount for the given
 * mountpoint and flags.
 *
 * @param mountpoint reference to the mount in the file system
 * @param options mount options
 * @return the FUSE file descriptor or -1 upon error
 */
int fuse_open_channel(const char *mountpoint, const char *options);

#ifdef __cplusplus
}
#endif

#endif /* FUSE_H_ */