fuse_lowlevel.h

UNIX/LINUX下面的用户文件系统

/*
    FUSE: Filesystem in Userspace
    Copyright (C) 2001-2006  Miklos Szeredi <[e-mail]>

    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 25 (recommended for any
   new application), to use the old API define it to 24 (default) */

#ifndef FUSE_USE_VERSION
#define FUSE_USE_VERSION 24
#endif

#include "fuse_common.h"

#include <utime.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);

    /**
     * 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