fusermount.c

FUSE文件系统开发工具,将内核层面的文件系统开发过程平移到应用层面上来。

	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;
}