fuse_lowlevel.h

Linux下fuse用户文件系统的的源代码

/*
    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 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'.
     *