fusermount.c

UNIX/LINUX下面的用户文件系统

                    (subtype ? strlen(subtype) : 0) + strlen(dev) + 32);

    type = malloc((subtype ? strlen(subtype) : 0) + 32);
    if (!type || !source) {
        fprintf(stderr, "%s: failed to allocate memory\n", progname);
        goto err;
    }

    if (subtype)
        sprintf(type, "%s.%s", blkdev ? "fuseblk" : "fuse", subtype);
    else
        strcpy(type, blkdev ? "fuseblk" : "fuse");

    if (fsname)
        strcpy(source, fsname);
    else
        strcpy(source, subtype ? subtype : dev);

    res = mount(source, mnt, type, flags, optbuf);
    if (res == -1 && errno == ENODEV && subtype) {
        /* Probably missing subtype support */
        strcpy(type, blkdev ? "fuseblk" : "fuse");
        if (fsname) {
            if (!blkdev)
                sprintf(source, "%s#%s", subtype, fsname);
        } else {
            strcpy(source, type);
        }

        res = mount(source, mnt, type, flags, optbuf);
    }
    if (res == -1 && errno == EINVAL) {
        /* It could be an old version not supporting group_id */
        sprintf(d, "fd=%i,rootmode=%o,user_id=%i", fd, rootmode, getuid());
        res = mount(source, mnt, type, flags, optbuf);
    }
    if (res == -1) {
        int errno_save = errno;
        if (blkdev && errno == ENODEV && !fuse_mnt_check_fuseblk())
            fprintf(stderr, "%s: 'fuseblk' support missing\n", progname);
        else
            fprintf(stderr, "%s: mount failed: %s\n", progname, strerror(errno_save));
        goto err;
    } else {
        *sourcep = source;
        *typep = type;
        *mnt_optsp = mnt_opts;
    }
    free(optbuf);

    return res;

 err:
    free(fsname);
    free(subtype);
    free(source);
    free(type);
    free(mnt_opts);
    free(optbuf);
    return -1;
}

static int check_version(const char *dev)
{
    int res;
    int majorver;
    int minorver;
    const char *version_file;
    FILE *vf;

    if (strcmp(dev, FUSE_DEV_OLD) != 0)
        return 0;

    version_file = FUSE_VERSION_FILE_OLD;
    vf = fopen(version_file, "r");
    if (vf == NULL) {
        fprintf(stderr, "%s: kernel interface too old\n", progname);
        return -1;
    }
    res = fscanf(vf, "%i.%i", &majorver, &minorver);
    fclose(vf);
    if (res != 2) {
        fprintf(stderr, "%s: error reading %s\n", progname, version_file);
        return -1;
    }
     if (majorver < 3) {
        fprintf(stderr, "%s: kernel interface too old\n", progname);
        return -1;
    }
    return 0;
}

static int check_perm(const char **mntp, struct stat *stbuf, int *currdir_fd,
                      int *mountpoint_fd)
{
    int res;
    const char *mnt = *mntp;
    const char *origmnt = mnt;

    res = lstat(mnt, stbuf);
    if (res == -1) {
        fprintf(stderr, "%s: failed to access mountpoint %s: %s\n",
                progname, mnt, strerror(errno));
        return -1;
    }

    /* No permission checking is done for root */
    if (getuid() == 0)
        return 0;

    if (S_ISDIR(stbuf->st_mode)) {
        *currdir_fd = open(".", O_RDONLY);
        if (*currdir_fd == -1) {
            fprintf(stderr, "%s: failed to open current directory: %s\n",
                    progname, strerror(errno));
            return -1;
        }
        res = chdir(mnt);
        if (res == -1) {
            fprintf(stderr, "%s: failed to chdir to mountpoint: %s\n",
                    progname, strerror(errno));
            return -1;
        }
        mnt = *mntp = ".";
        res = lstat(mnt, stbuf);
        if (res == -1) {
            fprintf(stderr, "%s: failed to access mountpoint %s: %s\n",
                    progname, origmnt, strerror(errno));
            return -1;
        }

        if ((stbuf->st_mode & S_ISVTX) && stbuf->st_uid != getuid()) {
            fprintf(stderr, "%s: mountpoint %s not owned by user\n",
                    progname, origmnt);
            return -1;
        }

        res = access(mnt, W_OK);
        if (res == -1) {
            fprintf(stderr, "%s: user has no write access to mountpoint %s\n",
                    progname, origmnt);
            return -1;
        }
    } else if (S_ISREG(stbuf->st_mode)) {
        static char procfile[256];
        *mountpoint_fd = open(mnt, O_WRONLY);
        if (*mountpoint_fd == -1) {
            fprintf(stderr, "%s: failed to open %s: %s\n", progname, mnt,
                    strerror(errno));
            return -1;
        }
        res = fstat(*mountpoint_fd, stbuf);
        if (res == -1) {
            fprintf(stderr, "%s: failed to access mountpoint %s: %s\n",
                    progname, mnt, strerror(errno));
            return -1;
        }
        if (!S_ISREG(stbuf->st_mode)) {
            fprintf(stderr, "%s: mountpoint %s is no longer a regular file\n",
                    progname, mnt);
            return -1;
        }

        sprintf(procfile, "/proc/self/fd/%i", *mountpoint_fd);
        *mntp = procfile;
    } else {
        fprintf(stderr,
                "%s: mountpoint %s is not a directory or a regular file\n",
                progname, mnt);
        return -1;
    }


    return 0;
}

static int try_open(const char *dev, char **devp, int silent)
{
    int fd = open(dev, O_RDWR);
    if (fd != -1) {
        *devp = strdup(dev);
        if (*devp == NULL) {
            fprintf(stderr, "%s: failed to allocate memory\n", progname);
            close(fd);
            fd = -1;
        }
    } else if (errno == ENODEV ||
               errno == ENOENT) /* check for ENOENT too, for the udev case */
        return -2;
    else if (!silent) {
        fprintf(stderr, "%s: failed to open %s: %s\n", progname, dev,
                strerror(errno));
    }
    return fd;
}

static int try_open_fuse_device(char **devp)
{
    int fd;
    int err;

    drop_privs();
    fd = try_open(FUSE_DEV_NEW, devp, 0);
    restore_privs();
    if (fd >= 0)
        return fd;

    err = fd;
    fd = try_open(FUSE_DEV_OLD, devp, 1);
    if (fd >= 0)
        return fd;

    return err;
}

static int open_fuse_device(char **devp)
{
    int fd = try_open_fuse_device(devp);
    if (fd >= -1)
        return fd;

    fprintf(stderr, "%s: fuse device not found, try 'modprobe fuse' first\n",
            progname);

    return -1;
}


static int mount_fuse(const char *mnt, const char *opts)
{
    int res;
    int fd;
    char *dev;
    struct stat stbuf;
    char *type = NULL;
    char *source = NULL;
    char *mnt_opts = NULL;
    const char *real_mnt = mnt;
    int currdir_fd = -1;
    int mountpoint_fd = -1;

    fd = open_fuse_device(&dev);
    if (fd == -1)
        return -1;

    drop_privs();
    read_conf();

    if (getuid() != 0 && mount_max != -1) {
        int mount_count = count_fuse_fs();
        if (mount_count >= mount_max) {
            fprintf(stderr, "%s: too many FUSE filesystems mounted; mount_max=N can be set in /etc/fuse.conf\n", progname);
            close(fd);
            return -1;
        }
    }

    res = check_version(dev);
    if (res != -1) {
        res = check_perm(&real_mnt, &stbuf, &currdir_fd, &mountpoint_fd);
        restore_privs();
        if (res != -1)
            res = do_mount(real_mnt, &type, stbuf.st_mode & S_IFMT, fd, opts,
                           dev, &source, &mnt_opts, stbuf.st_size);
    } else
        restore_privs();

    if (currdir_fd != -1) {
        fchdir(currdir_fd);
        close(currdir_fd);
    }
    if (mountpoint_fd != -1)
        close(mountpoint_fd);

    if (res == -1) {
        close(fd);
        return -1;
    }

    if (geteuid() == 0) {
        res = add_mount(source, mnt, type, mnt_opts);
        if (res == -1) {
            umount2(mnt, 2); /* lazy umount */
            close(fd);
            return -1;
        }
    }

    free(source);
    free(type);
    free(mnt_opts);
    free(dev);

    return fd;
}

static int send_fd(int sock_fd, int fd)
{
    int retval;
    struct msghdr msg;
    struct cmsghdr *p_cmsg;
    struct iovec vec;
    size_t cmsgbuf[CMSG_SPACE(sizeof(fd)) / sizeof(size_t)];
    int *p_fds;
    char sendchar = 0;

    msg.msg_control = cmsgbuf;
    msg.msg_controllen = sizeof(cmsgbuf);
    p_cmsg = CMSG_FIRSTHDR(&msg);
    p_cmsg->cmsg_level = SOL_SOCKET;
    p_cmsg->cmsg_type = SCM_RIGHTS;
    p_cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
    p_fds = (int *) CMSG_DATA(p_cmsg);
    *p_fds = fd;
    msg.msg_controllen = p_cmsg->cmsg_len;
    msg.msg_name = NULL;
    msg.msg_namelen = 0;
    msg.msg_iov = &vec;
    msg.msg_iovlen = 1;
    msg.msg_flags = 0;
    /* "To pass file descriptors or credentials you need to send/read at
     * least one byte" (man 7 unix) */
    vec.iov_base = &sendchar;
    vec.iov_len = sizeof(sendchar);
    while ((retval = sendmsg(sock_fd, &msg, 0)) == -1 && errno == EINTR);
    if (retval != 1) {
        perror("sending file descriptor");
        return -1;
    }
    return 0;
}

static void usage(void)
{
    fprintf(stderr,
            "%s: [options] mountpoint\n"
            "Options:\n"
            " -h                print help\n"
            " -V                print version\n"
            " -o opt[,opt...]   mount options\n"
            " -u                unmount\n"
            " -q                quiet\n"
            " -z                lazy unmount\n",
            progname);
    exit(1);
}

static void show_version(void)
{
    printf("fusermount version: %s\n", PACKAGE_VERSION);
    exit(0);
}

int main(int argc, char *argv[])
{
    int ch;
    int fd;
    int res;
    char *origmnt;
    char *mnt;
    static int unmount = 0;
    static int lazy = 0;
    static int quiet = 0;
    char *commfd;
    int cfd;
    const char *opts = "";

    static const struct option long_opts[] = {
        {"unmount", no_argument, NULL, 'u'},
        {"lazy",    no_argument, NULL, 'z'},
        {"quiet",   no_argument, NULL, 'q'},
        {"help",    no_argument, NULL, 'h'},
        {"version", no_argument, NULL, 'V'},
        {0, 0, 0, 0}};

    progname = strdup(argv[0]);
    if (progname == NULL) {
        fprintf(stderr, "%s: failed to allocate memory\n", argv[0]);
        exit(1);
    }

    while ((ch = getopt_long(argc, argv, "hVo:uzq", long_opts, NULL)) != -1) {
        switch (ch) {
        case 'h':
            usage();
            break;

        case 'V':
            show_version();
            break;

        case 'o':
            opts = optarg;
            break;

        case 'u':
            unmount = 1;
            break;

        case 'z':
            lazy = 1;
            break;

        case 'q':
            quiet = 1;
            break;

        default:
            exit(1);
        }
    }

    if (lazy && !unmount) {
        fprintf(stderr, "%s: -z can only be used with -u\n", progname);
        exit(1);
    }

    if (optind >= argc) {
        fprintf(stderr, "%s: missing mountpoint argument\n", progname);
        exit(1);
    }

    origmnt = argv[optind];

    drop_privs();
    mnt = fuse_mnt_resolve_path(progname, origmnt);
    restore_privs();
    if (mnt == NULL)
        exit(1);

    umask(033);
    if (unmount) {
        if (geteuid() == 0)
            res = unmount_fuse(mnt, quiet, lazy);
        else {
            res = umount2(mnt, lazy ? 2 : 0);
            if (res == -1 && !quiet)
                fprintf(stderr, "%s: failed to unmount %s: %s\n", progname,
                        mnt, strerror(errno));
        }
        if (res == -1)
            exit(1);
        return 0;
    }

    commfd = getenv(FUSE_COMMFD_ENV);
    if (commfd == NULL) {
        fprintf(stderr, "%s: old style mounting not supported\n", progname);
        exit(1);
    }

    fd = mount_fuse(mnt, opts);
    if (fd == -1)
        exit(1);

    cfd = atoi(commfd);
    res = send_fd(cfd, fd);
    if (res == -1)
        exit(1);

    return 0;
}