C++ path_put函数代码示例

//.........这里部分代码省略.........
		err = -ENOENT;
		goto out_free;
	}

	/* set the lower superblock field of upper superblock */
	bstart = lower_root_info->bstart;
	BUG_ON(bstart != 0);
	sbend(sb) = bend = lower_root_info->bend;
	for (bindex = bstart; bindex <= bend; bindex++) {
		struct dentry *d = lower_root_info->lower_paths[bindex].dentry;
		atomic_inc(&d->d_sb->s_active);
		unionfs_set_lower_super_idx(sb, bindex, d->d_sb);
	}

	/* max Bytes is the maximum bytes from highest priority branch */
	sb->s_maxbytes = unionfs_lower_super_idx(sb, 0)->s_maxbytes;

	/*
	 * Our c/m/atime granularity is 1 ns because we may stack on file
	 * systems whose granularity is as good.  This is important for our
	 * time-based cache coherency.
	 */
	sb->s_time_gran = 1;

	sb->s_op = &unionfs_sops;

	/* See comment next to the definition of unionfs_d_alloc_root */
	sb->s_root = unionfs_d_alloc_root(sb);
	if (unlikely(!sb->s_root)) {
		err = -ENOMEM;
		goto out_dput;
	}

	/* link the upper and lower dentries */
	sb->s_root->d_fsdata = NULL;
	err = new_dentry_private_data(sb->s_root, UNIONFS_DMUTEX_ROOT);
	if (unlikely(err))
		goto out_freedpd;

	/* Set the lower dentries for s_root */
	for (bindex = bstart; bindex <= bend; bindex++) {
		struct dentry *d;
		struct vfsmount *m;

		d = lower_root_info->lower_paths[bindex].dentry;
		m = lower_root_info->lower_paths[bindex].mnt;

		unionfs_set_lower_dentry_idx(sb->s_root, bindex, d);
		unionfs_set_lower_mnt_idx(sb->s_root, bindex, m);
	}
	dbstart(sb->s_root) = bstart;
	dbend(sb->s_root) = bend;

	/* Set the generation number to one, since this is for the mount. */
	atomic_set(&UNIONFS_D(sb->s_root)->generation, 1);

	/*
	 * Call interpose to create the upper level inode.  Only
	 * INTERPOSE_LOOKUP can return a value other than 0 on err.
	 */
	err = PTR_ERR(unionfs_interpose(sb->s_root, sb, 0));
	unionfs_unlock_dentry(sb->s_root);
	if (!err)
		goto out;
	/* else fall through */

out_freedpd:
	if (UNIONFS_D(sb->s_root)) {
		kfree(UNIONFS_D(sb->s_root)->lower_paths);
		free_dentry_private_data(sb->s_root);
	}
	dput(sb->s_root);

out_dput:
	if (lower_root_info && !IS_ERR(lower_root_info)) {
		for (bindex = lower_root_info->bstart;
		     bindex <= lower_root_info->bend; bindex++) {
			struct dentry *d;
			d = lower_root_info->lower_paths[bindex].dentry;
			/* drop refs we took earlier */
			atomic_dec(&d->d_sb->s_active);
			path_put(&lower_root_info->lower_paths[bindex]);
		}
		kfree(lower_root_info->lower_paths);
		kfree(lower_root_info);
		lower_root_info = NULL;
	}

out_free:
	kfree(UNIONFS_SB(sb)->data);
	kfree(UNIONFS_SB(sb));
	sb->s_fs_info = NULL;

out:
	if (lower_root_info && !IS_ERR(lower_root_info)) {
		kfree(lower_root_info->lower_paths);
		kfree(lower_root_info);
	}
	return err;
}

/**
 * ccs_get_absolute_path - Get the path of a dentry but ignores chroot'ed root.
 *
 * @path:   Pointer to "struct path".
 * @buffer: Pointer to buffer to return value in.
 * @buflen: Sizeof @buffer.
 *
 * Returns the buffer on success, an error code otherwise.
 *
 * Caller holds the dcache_lock and vfsmount_lock.
 * Based on __d_path() in fs/dcache.c
 *
 * If dentry is a directory, trailing '/' is appended.
 */
static char *ccs_get_absolute_path(struct path *path, char * const buffer,
				   const int buflen)
{
#if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 2, 0)
	char *pos = ERR_PTR(-ENOMEM);
	if (buflen >= 256) {
		pos = ccsecurity_exports.d_absolute_path(path, buffer,
							 buflen - 1);
		if (!IS_ERR(pos) && *pos == '/' && pos[1]) {
			struct inode *inode = path->dentry->d_inode;
			if (inode && S_ISDIR(inode->i_mode)) {
				buffer[buflen - 2] = '/';
				buffer[buflen - 1] = '\0';
			}
		}
	}
	return pos;
#elif LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 36)
	/*
	 * __d_path() will start returning NULL by backporting commit 02125a82
	 * "fix apparmor dereferencing potentially freed dentry, sanitize
	 * __d_path() API".
	 *
	 * Unfortunately, __d_path() after applying that commit always returns
	 * NULL when root is empty. d_absolute_path() is provided for TOMOYO
	 * 2.x and AppArmor but TOMOYO 1.x does not use it, for TOMOYO 1.x
	 * might be built as a loadable kernel module and there is no warrantee
	 * that TOMOYO 1.x is recompiled after applying that commit. Also,
	 * I don't want to search /proc/kallsyms for d_absolute_path() because
	 * I want to keep TOMOYO 1.x architecture independent. Thus, supply
	 * non empty root like AppArmor's d_namespace_path() did.
	 */
	char *pos = ERR_PTR(-ENOMEM);
	if (buflen >= 256) {
		static bool ccs_no_empty;
		if (!ccs_no_empty) {
			struct path root = { };
			pos = ccsecurity_exports.__d_path(path, &root, buffer,
							  buflen - 1);
		} else {
			pos = NULL;
		}
		if (!pos) {
			struct task_struct *task = current;
			struct path root;
			struct path tmp;
			spin_lock(&task->fs->lock);
			root.mnt = task->nsproxy->mnt_ns->root;
			root.dentry = root.mnt->mnt_root;
			path_get(&root);
			spin_unlock(&task->fs->lock);
			tmp = root;
			pos = ccsecurity_exports.__d_path(path, &tmp, buffer,
							  buflen - 1);
			path_put(&root);
			if (!pos)
				return ERR_PTR(-EINVAL);
			/* Remember if __d_path() needs non empty root. */
			ccs_no_empty = true;
		}
		if (!IS_ERR(pos) && *pos == '/' && pos[1]) {
			struct inode *inode = path->dentry->d_inode;
			if (inode && S_ISDIR(inode->i_mode)) {
				buffer[buflen - 2] = '/';
				buffer[buflen - 1] = '\0';
			}
		}
	}
	return pos;
#else
	char *pos = buffer + buflen - 1;
	struct dentry *dentry = path->dentry;
	struct vfsmount *vfsmnt = path->mnt;
	const char *name;
	int len;

	if (buflen < 256)
		goto out;

	*pos = '\0';
	if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode))
		*--pos = '/';
	for (;;) {
		struct dentry *parent;
		if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
			if (vfsmnt->mnt_parent == vfsmnt)
//.........这里部分代码省略.........

static int do_dentry_open(struct file *f,
			  int (*open)(struct inode *, struct file *),
			  const struct cred *cred)
{
	static const struct file_operations empty_fops = {};
	struct inode *inode;
	int error;

	f->f_mode = OPEN_FMODE(f->f_flags) | FMODE_LSEEK |
				FMODE_PREAD | FMODE_PWRITE;

	if (unlikely(f->f_flags & O_PATH))
		f->f_mode = FMODE_PATH;

	path_get(&f->f_path);
	inode = f->f_path.dentry->d_inode;
	if (f->f_mode & FMODE_WRITE) {
		error = __get_file_write_access(inode, f->f_path.mnt);
		if (error)
			goto cleanup_file;
		if (!special_file(inode->i_mode))
			file_take_write(f);
	}

	f->f_mapping = inode->i_mapping;
	f->f_pos = 0;
	file_sb_list_add(f, inode->i_sb);

	if (unlikely(f->f_mode & FMODE_PATH)) {
		f->f_op = &empty_fops;
		return 0;
	}

	f->f_op = fops_get(inode->i_fop);

	error = security_file_open(f, cred);
	if (error)
		goto cleanup_all;

	error = break_lease(inode, f->f_flags);
	if (error)
		goto cleanup_all;

	if (!open && f->f_op)
		open = f->f_op->open;
	if (open) {
		error = open(inode, f);
		if (error)
			goto cleanup_all;
	}
	if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
		i_readcount_inc(inode);

	f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);

	file_ra_state_init(&f->f_ra, f->f_mapping->host->i_mapping);

	return 0;

cleanup_all:
	fops_put(f->f_op);
	file_sb_list_del(f);
	if (f->f_mode & FMODE_WRITE) {
		put_write_access(inode);
		if (!special_file(inode->i_mode)) {
			/*
			 * We don't consider this a real
			 * mnt_want/drop_write() pair
			 * because it all happenend right
			 * here, so just reset the state.
			 */
			file_reset_write(f);
			__mnt_drop_write(f->f_path.mnt);
		}
	}
cleanup_file:
	path_put(&f->f_path);
	f->f_path.mnt = NULL;
	f->f_path.dentry = NULL;
	return error;
}

/*
 * access() needs to use the real uid/gid, not the effective uid/gid.
 * We do this by temporarily clearing all FS-related capabilities and
 * switching the fsuid/fsgid around to the real ones.
 */
SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
{
	const struct cred *old_cred;
	struct cred *override_cred;
	struct path path;
	struct inode *inode;
	int res;

	if (mode & ~S_IRWXO)	/* where's F_OK, X_OK, W_OK, R_OK? */
		return -EINVAL;

	override_cred = prepare_creds();
	if (!override_cred)
		return -ENOMEM;

	override_cred->fsuid = override_cred->uid;
	override_cred->fsgid = override_cred->gid;

	if (!issecure(SECURE_NO_SETUID_FIXUP)) {
		/* Clear the capabilities if we switch to a non-root user */
		if (override_cred->uid)
			cap_clear(override_cred->cap_effective);
		else
			override_cred->cap_effective =
				override_cred->cap_permitted;
	}

	old_cred = override_creds(override_cred);

	res = user_path_at(dfd, filename, LOOKUP_FOLLOW, &path);
	if (res)
		goto out;

	inode = path.dentry->d_inode;

	if ((mode & MAY_EXEC) && S_ISREG(inode->i_mode)) {
		/*
		 * MAY_EXEC on regular files is denied if the fs is mounted
		 * with the "noexec" flag.
		 */
		res = -EACCES;
		if (path.mnt->mnt_flags & MNT_NOEXEC)
			goto out_path_release;
	}

	res = inode_permission(inode, mode | MAY_ACCESS);
	/* SuS v2 requires we report a read only fs too */
	if (res || !(mode & S_IWOTH) || special_file(inode->i_mode))
		goto out_path_release;
	/*
	 * This is a rare case where using __mnt_is_readonly()
	 * is OK without a mnt_want/drop_write() pair.  Since
	 * no actual write to the fs is performed here, we do
	 * not need to telegraph to that to anyone.
	 *
	 * By doing this, we accept that this access is
	 * inherently racy and know that the fs may change
	 * state before we even see this result.
	 */
	if (__mnt_is_readonly(path.mnt))
		res = -EROFS;

out_path_release:
	path_put(&path);
out:
	revert_creds(old_cred);
	put_cred(override_cred);
	return res;
}

//.........这里部分代码省略.........
        goto out_put_workpath;
    }
    ufs->lower_namelen = statfs.f_namelen;

    sb->s_stack_depth = max(upperpath.mnt->mnt_sb->s_stack_depth,
                            lowerpath.mnt->mnt_sb->s_stack_depth) + 1;

    err = -EINVAL;
    if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
        pr_err("overlayfs: maximum fs stacking depth exceeded\n");
        goto out_put_workpath;
    }

    ufs->upper_mnt = clone_private_mount(&upperpath);
    err = PTR_ERR(ufs->upper_mnt);
    if (IS_ERR(ufs->upper_mnt)) {
        pr_err("overlayfs: failed to clone upperpath\n");
        goto out_put_workpath;
    }

    ufs->lower_mnt = clone_private_mount(&lowerpath);
    err = PTR_ERR(ufs->lower_mnt);
    if (IS_ERR(ufs->lower_mnt)) {
        pr_err("overlayfs: failed to clone lowerpath\n");
        goto out_put_upper_mnt;
    }

    ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
    err = PTR_ERR(ufs->workdir);
    if (IS_ERR(ufs->workdir)) {
        if (err == -ENOSPC || err == -EROFS) {
            pr_warning("overlayfs: failed to create work directory (%s), mounting read-only\n", err == ENOSPC ? "ENOSPC" : "EROFS");
            sb->s_flags |= MS_RDONLY;
            ufs->workdir = NULL;
        } else {
            pr_err("overlayfs: failed to create directory %s/%s\n",
                   ufs->config.workdir, OVL_WORKDIR_NAME);
            goto out_put_lower_mnt;
        }
    }

    /*
     * Make lower_mnt R/O.  That way fchmod/fchown on lower file
     * will fail instead of modifying lower fs.
     */
    ufs->lower_mnt->mnt_flags |= MNT_READONLY;

    /* If the upper fs is r/o, we mark overlayfs r/o too */
    if (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY)
        sb->s_flags |= MS_RDONLY;

    sb->s_d_op = &ovl_dentry_operations;

    err = -ENOMEM;
    root_inode = ovl_new_inode(sb, S_IFDIR, oe);
    if (!root_inode)
        goto out_put_workdir;

    root_dentry = d_make_root(root_inode);
    if (!root_dentry)
        goto out_put_workdir;

    mntput(upperpath.mnt);
    mntput(lowerpath.mnt);
    path_put(&workpath);

    oe->__upperdentry = upperpath.dentry;
    oe->lowerdentry = lowerpath.dentry;

    root_dentry->d_fsdata = oe;

    sb->s_magic = OVERLAYFS_SUPER_MAGIC;
    sb->s_op = &ovl_super_operations;
    sb->s_root = root_dentry;
    sb->s_fs_info = ufs;

    return 0;

out_put_workdir:
    dput(ufs->workdir);
out_put_lower_mnt:
    mntput(ufs->lower_mnt);
out_put_upper_mnt:
    mntput(ufs->upper_mnt);
out_put_workpath:
    path_put(&workpath);
out_put_lowerpath:
    path_put(&lowerpath);
out_put_upperpath:
    path_put(&upperpath);
out_free_oe:
    kfree(oe);
out_free_config:
    kfree(ufs->config.lowerdir);
    kfree(ufs->config.upperdir);
    kfree(ufs->config.workdir);
    kfree(ufs);
out:
    return err;
}

int devtmpfs_create_node(struct device *dev)
{
	const char *tmp = NULL;
	const char *nodename;
	const struct cred *curr_cred;
	mode_t mode = 0;
	struct nameidata nd;
	struct dentry *dentry;
	int err;

	if (!dev_mnt)
		return 0;

	nodename = device_get_devnode(dev, &mode, &tmp);
	if (!nodename)
		return -ENOMEM;

	if (mode == 0)
		mode = 0600;
	if (is_blockdev(dev))
		mode |= S_IFBLK;
	else
		mode |= S_IFCHR;

	curr_cred = override_creds(&init_cred);

	err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
			      nodename, LOOKUP_PARENT, &nd);
	if (err == -ENOENT) {
		create_path(nodename);
		err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
				      nodename, LOOKUP_PARENT, &nd);
	}
	if (err)
		goto out;

	dentry = lookup_create(&nd, 0);
	if (!IS_ERR(dentry)) {
		err = vfs_mknod(nd.path.dentry->d_inode,
				dentry, mode, dev->devt);
		if (!err) {
			struct iattr newattrs;

			/* fixup possibly umasked mode */
			newattrs.ia_mode = mode;
			newattrs.ia_valid = ATTR_MODE;
			mutex_lock(&dentry->d_inode->i_mutex);
			notify_change(dentry, &newattrs);
			mutex_unlock(&dentry->d_inode->i_mutex);

			/* mark as kernel-created inode */
			dentry->d_inode->i_private = &dev_mnt;
		}
		dput(dentry);
	} else {
		err = PTR_ERR(dentry);
	}

	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
	path_put(&nd.path);
out:
	kfree(tmp);
	revert_creds(curr_cred);
	return err;
}

/**
 * d_namespace_path - lookup a name associated with a given path
 * @path: path to lookup  (NOT NULL)
 * @buf:  buffer to store path to  (NOT NULL)
 * @buflen: length of @buf
 * @name: Returns - pointer for start of path name with in @buf (NOT NULL)
 * @flags: flags controlling path lookup
 *
 * Handle path name lookup.
 *
 * Returns: %0 else error code if path lookup fails
 *          When no error the path name is returned in @name which points to
 *          to a position in @buf
 */
static int d_namespace_path(struct path *path, char *buf, int buflen,
			    char **name, int flags)
{
	struct path root, tmp;
	char *res;
	int connected, error = 0;

	/* Get the root we want to resolve too, released below */
	if (flags & PATH_CHROOT_REL) {
		/* resolve paths relative to chroot */
		get_fs_root(current->fs, &root);
	} else {
		/* resolve paths relative to namespace */
		root.mnt = current->nsproxy->mnt_ns->root;
		root.dentry = root.mnt->mnt_root;
		path_get(&root);
	}

	spin_lock(&dcache_lock);
	tmp = root;
	res = __d_path(path, &tmp, buf, buflen);
	spin_unlock(&dcache_lock);

	*name = res;
	/* handle error conditions - and still allow a partial path to
	 * be returned.
	 */
	if (IS_ERR(res)) {
		error = PTR_ERR(res);
		*name = buf;
		goto out;
	}

	/* Handle two cases:
	 * 1. A deleted dentry && profile is not allowing mediation of deleted
	 * 2. On some filesystems, newly allocated dentries appear to the
	 *    security_path hooks as a deleted dentry except without an inode
	 *    allocated.
	 */
	if (d_unlinked(path->dentry) && path->dentry->d_inode &&
	    !(flags & PATH_MEDIATE_DELETED)) {
			error = -ENOENT;
			goto out;
	}

	/* Determine if the path is connected to the expected root */
	connected = tmp.dentry == root.dentry && tmp.mnt == root.mnt;

	/* If the path is not connected,
	 * check if it is a sysctl and handle specially else remove any
	 * leading / that __d_path may have returned.
	 * Unless
	 *     specifically directed to connect the path,
	 * OR
	 *     if in a chroot and doing chroot relative paths and the path
	 *     resolves to the namespace root (would be connected outside
	 *     of chroot) and specifically directed to connect paths to
	 *     namespace root.
	 */
	if (!connected) {
		/* is the disconnect path a sysctl? */
		if (tmp.dentry->d_sb->s_magic == PROC_SUPER_MAGIC &&
		    strncmp(*name, "/sys/", 5) == 0) {
			/* TODO: convert over to using a per namespace
			 * control instead of hard coded /proc
			 */
			error = prepend(name, *name - buf, "/proc", 5);
		} else if (!(flags & PATH_CONNECT_PATH) &&
			   !(((flags & CHROOT_NSCONNECT) == CHROOT_NSCONNECT) &&
			     (tmp.mnt == current->nsproxy->mnt_ns->root &&
			      tmp.dentry == tmp.mnt->mnt_root))) {
			/* disconnected path, don't return pathname starting
			 * with '/'
			 */
			error = -ESTALE;
			if (*res == '/')
				*name = res + 1;
		}
	}

out:
	path_put(&root);

	return error;
}

/*
 * access() needs to use the real uid/gid, not the effective uid/gid.
 * We do this by temporarily clearing all FS-related capabilities and
 * switching the fsuid/fsgid around to the real ones.
 */
asmlinkage long sys_faccessat(int dfd, const char __user *filename, int mode)
{
    struct nameidata nd;
    int old_fsuid, old_fsgid;
    kernel_cap_t uninitialized_var(old_cap);  /* !SECURE_NO_SETUID_FIXUP */
    int res;

    if (mode & ~S_IRWXO)    /* where's F_OK, X_OK, W_OK, R_OK? */
        return -EINVAL;

    old_fsuid = current->fsuid;
    old_fsgid = current->fsgid;

    current->fsuid = current->uid;
    current->fsgid = current->gid;

    if (!issecure(SECURE_NO_SETUID_FIXUP)) {
        /*
         * Clear the capabilities if we switch to a non-root user
         */
#ifndef CONFIG_SECURITY_FILE_CAPABILITIES
        /*
         * FIXME: There is a race here against sys_capset.  The
         * capabilities can change yet we will restore the old
         * value below.  We should hold task_capabilities_lock,
         * but we cannot because user_path_walk can sleep.
         */
#endif /* ndef CONFIG_SECURITY_FILE_CAPABILITIES */
        if (current->uid)
            old_cap = cap_set_effective(__cap_empty_set);
        else
            old_cap = cap_set_effective(current->cap_permitted);
    }

    res = __user_walk_fd(dfd, filename, LOOKUP_FOLLOW|LOOKUP_ACCESS, &nd);
    if (res)
        goto out;

    res = vfs_permission(&nd, mode);
    /* SuS v2 requires we report a read only fs too */
    if(res || !(mode & S_IWOTH) ||
       special_file(nd.path.dentry->d_inode->i_mode))
        goto out_path_release;
    /*
     * This is a rare case where using __mnt_is_readonly()
     * is OK without a mnt_want/drop_write() pair.  Since
     * no actual write to the fs is performed here, we do
     * not need to telegraph to that to anyone.
     *
     * By doing this, we accept that this access is
     * inherently racy and know that the fs may change
     * state before we even see this result.
     */
    if (__mnt_is_readonly(nd.path.mnt))
        res = -EROFS;

out_path_release:
    path_put(&nd.path);
out:
    current->fsuid = old_fsuid;
    current->fsgid = old_fsgid;

    if (!issecure(SECURE_NO_SETUID_FIXUP))
        cap_set_effective(old_cap);

    return res;
}

static struct dentry *lofs_mount(
    struct file_system_type *fs_type,
    int flags,
    const char *dev_name,
    void *raw_data)
{
    static const struct qstr slash = { .name = "/", .len = 1 };
    struct super_block *s;
    struct lofs_sb_info *sbi;
    struct lofs_dentry_info *root_info;
    struct inode *inode;
    const char *err = "Getting sb failed";
    struct path path;
    int rc;

    sbi = kmem_cache_zalloc(lofs_sb_info_cache, GFP_KERNEL);
    if (!sbi) {
        rc = -ENOMEM;
        goto out;
    }

    s = sget(fs_type, NULL, set_anon_super, NULL);
    if (IS_ERR(s)) {
        rc = PTR_ERR(s);
        goto out;
    }

    s->s_flags = flags;
#if defined(HAVE_BACKING_DEV)
    rc = bdi_setup_and_register(&sbi->bdi, "lofs", BDI_CAP_MAP_COPY);
    if (rc)
        goto out1;

    s->s_bdi = &sbi->bdi;
#endif
    lofs_set_superblock_private(s, sbi);

    /* ->kill_sb() will take care of sbi after that point */
    sbi = NULL;
    s->s_op   = &lofs_sops;
    s->s_d_op = &lofs_dops;

    err = "Reading sb failed";
    rc = kern_path(slash.name, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path);
    if (rc) {
        lofs_printk(KERN_WARNING, "kern_path() failed\n");
        goto out1;
    }

    lofs_set_superblock_lower(s, path.dentry->d_sb);
    s->s_maxbytes = path.dentry->d_sb->s_maxbytes;
    s->s_blocksize = path.dentry->d_sb->s_blocksize;
    s->s_magic = 0x10f5;

    inode = lofs_get_inode(path.dentry->d_inode, s);
    rc = PTR_ERR(inode);
    if (IS_ERR(inode)) {
        goto out_free;
    }

#ifdef HAVE_D_MAKE_ROOT
    s->s_root = d_make_root(inode);
#else
    s->s_root = d_alloc_root(inode);
    if (!s->s_root) {
        iput(inode);
    }
#endif
    if (!s->s_root) {
        rc = -ENOMEM;
        goto out_free;
    }

    rc = -ENOMEM;
    root_info = kmem_cache_zalloc(lofs_dentry_info_cache, GFP_KERNEL);
    if (!root_info)
        goto out_free;

    /* ->kill_sb() will take care of root_info */
    lofs_set_dentry_private(s->s_root, root_info);
    lofs_set_dentry_lower(s->s_root, path.dentry);
    lofs_set_dentry_lower_mnt(s->s_root, path.mnt);

    s->s_flags |= MS_ACTIVE;
    return dget(s->s_root);

out_free:
    path_put(&path);
out1:
    deactivate_locked_super(s);
out:
    if (sbi) {
        kmem_cache_free(lofs_sb_info_cache, sbi);
    }
    printk(KERN_ERR "%s; rc = [%d]\n", err, rc);
    return ERR_PTR(rc);
}

/**
 * lofs_kill_block_super
//.........这里部分代码省略.........

static long do_sys_truncate(const char __user * path, loff_t length)
{
    struct nameidata nd;
    struct inode * inode;
    int error;

    error = -EINVAL;
    if (length < 0)    /* sorry, but loff_t says... */
        goto out;

    error = user_path_walk(path, &nd);
    if (error)
        goto out;
    inode = nd.path.dentry->d_inode;

    /* For directories it's -EISDIR, for other non-regulars - -EINVAL */
    error = -EISDIR;
    if (S_ISDIR(inode->i_mode))
        goto dput_and_out;

    error = -EINVAL;
    if (!S_ISREG(inode->i_mode))
        goto dput_and_out;

    error = mnt_want_write(nd.path.mnt);
    if (error)
        goto dput_and_out;

    error = vfs_permission(&nd, MAY_WRITE);
    if (error)
        goto mnt_drop_write_and_out;

    error = -EPERM;
    if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
        goto mnt_drop_write_and_out;

    error = get_write_access(inode);
    if (error)
        goto mnt_drop_write_and_out;

    /*
     * Make sure that there are no leases.  get_write_access() protects
     * against the truncate racing with a lease-granting setlease().
     */
    error = break_lease(inode, FMODE_WRITE);
    if (error)
        goto put_write_and_out;

    error = locks_verify_truncate(inode, NULL, length);
    if (!error) {
        DQUOT_INIT(inode);
        error = do_truncate(nd.path.dentry, length, 0, NULL);
    }

put_write_and_out:
    put_write_access(inode);
mnt_drop_write_and_out:
    mnt_drop_write(nd.path.mnt);
dput_and_out:
    path_put(&nd.path);
out:
    return error;
}

/*
 * xfs_find_handle maps from userspace xfs_fsop_handlereq structure to
 * a file or fs handle.
 *
 * XFS_IOC_PATH_TO_FSHANDLE
 *    returns fs handle for a mount point or path within that mount point
 * XFS_IOC_FD_TO_HANDLE
 *    returns full handle for a FD opened in user space
 * XFS_IOC_PATH_TO_HANDLE
 *    returns full handle for a path
 */
STATIC int
xfs_find_handle(
	unsigned int		cmd,
	void			__user *arg)
{
	int			hsize;
	xfs_handle_t		handle;
	xfs_fsop_handlereq_t	hreq;
	struct inode		*inode;

	if (copy_from_user(&hreq, arg, sizeof(hreq)))
		return -XFS_ERROR(EFAULT);

	memset((char *)&handle, 0, sizeof(handle));

	switch (cmd) {
	case XFS_IOC_PATH_TO_FSHANDLE:
	case XFS_IOC_PATH_TO_HANDLE: {
		struct path path;
		int error = user_lpath((const char __user *)hreq.path, &path);
		if (error)
			return error;

		ASSERT(path.dentry);
		ASSERT(path.dentry->d_inode);
		inode = igrab(path.dentry->d_inode);
		path_put(&path);
		break;
	}

	case XFS_IOC_FD_TO_HANDLE: {
		struct file	*file;

		file = fget(hreq.fd);
		if (!file)
		    return -EBADF;

		ASSERT(file->f_path.dentry);
		ASSERT(file->f_path.dentry->d_inode);
		inode = igrab(file->f_path.dentry->d_inode);
		fput(file);
		break;
	}

	default:
		ASSERT(0);
		return -XFS_ERROR(EINVAL);
	}

	if (inode->i_sb->s_magic != XFS_SB_MAGIC) {
		/* we're not in XFS anymore, Toto */
		iput(inode);
		return -XFS_ERROR(EINVAL);
	}

	switch (inode->i_mode & S_IFMT) {
	case S_IFREG:
	case S_IFDIR:
	case S_IFLNK:
		break;
	default:
		iput(inode);
		return -XFS_ERROR(EBADF);
	}

	/* now we can grab the fsid */
	memcpy(&handle.ha_fsid, XFS_I(inode)->i_mount->m_fixedfsid,
			sizeof(xfs_fsid_t));
	hsize = sizeof(xfs_fsid_t);

	if (cmd != XFS_IOC_PATH_TO_FSHANDLE) {
		xfs_inode_t	*ip = XFS_I(inode);
		int		lock_mode;

		/* need to get access to the xfs_inode to read the generation */
		lock_mode = xfs_ilock_map_shared(ip);

		/* fill in fid section of handle from inode */
		handle.ha_fid.fid_len = sizeof(xfs_fid_t) -
					sizeof(handle.ha_fid.fid_len);
		handle.ha_fid.fid_pad = 0;
		handle.ha_fid.fid_gen = ip->i_d.di_gen;
		handle.ha_fid.fid_ino = ip->i_ino;

		xfs_iunlock_map_shared(ip, lock_mode);

		hsize = XFS_HSIZE(handle);
	}

//.........这里部分代码省略.........

static void * nfs_follow_mountpoint(struct dentry *dentry, struct nameidata *nd)
{
	struct vfsmount *mnt;
	struct nfs_server *server = NFS_SERVER(dentry->d_inode);
	struct dentry *parent;
	struct nfs_fh *fh = NULL;
	struct nfs_fattr *fattr = NULL;
	int err;

	dprintk("--> nfs_follow_mountpoint()\n");

	err = -ESTALE;
	if (IS_ROOT(dentry))
		goto out_err;

	err = -ENOMEM;
	fh = nfs_alloc_fhandle();
	fattr = nfs_alloc_fattr();
	if (fh == NULL || fattr == NULL)
		goto out_err;

	dprintk("%s: enter\n", __func__);
	dput(nd->path.dentry);
	nd->path.dentry = dget(dentry);

	/* Look it up again */
	parent = dget_parent(nd->path.dentry);
	err = server->nfs_client->rpc_ops->lookup(parent->d_inode,
						  &nd->path.dentry->d_name,
						  fh, fattr);
	dput(parent);
	if (err != 0)
		goto out_err;

	if (fattr->valid & NFS_ATTR_FATTR_V4_REFERRAL)
		mnt = nfs_do_refmount(nd->path.mnt, nd->path.dentry);
	else
		mnt = nfs_do_submount(nd->path.mnt, nd->path.dentry, fh,
				      fattr);
	err = PTR_ERR(mnt);
	if (IS_ERR(mnt))
		goto out_err;

	mntget(mnt);
	err = do_add_mount(mnt, &nd->path, nd->path.mnt->mnt_flags|MNT_SHRINKABLE,
			   &nfs_automount_list);
	if (err < 0) {
		mntput(mnt);
		if (err == -EBUSY)
			goto out_follow;
		goto out_err;
	}
	path_put(&nd->path);
	nd->path.mnt = mnt;
	nd->path.dentry = dget(mnt->mnt_root);
	schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout);
out:
	nfs_free_fattr(fattr);
	nfs_free_fhandle(fh);
	dprintk("%s: done, returned %d\n", __func__, err);

	dprintk("<-- nfs_follow_mountpoint() = %d\n", err);
	return ERR_PTR(err);
out_err:
	path_put(&nd->path);
	goto out;
out_follow:
	while (d_mountpoint(nd->path.dentry) &&
	       follow_down(&nd->path))
		;
	err = 0;
	goto out;
}

//.........这里部分代码省略.........
	if (IS_ERR(inode)) {
		err = PTR_ERR(inode);
		goto out_sput;
	}
	sb->s_root = d_make_root(inode);
	if (!sb->s_root) {
		err = -ENOMEM;
		goto out_iput;
	}
	d_set_d_op(sb->s_root, &esdfs_dops);

	/* link the upper and lower dentries */
	sb->s_root->d_fsdata = NULL;
	err = new_dentry_private_data(sb->s_root);
	if (err)
		goto out_freeroot;

	/* if get here: cannot have error */

	/* set the lower dentries for s_root */
	esdfs_set_lower_path(sb->s_root, &lower_path);
#ifdef CONFIG_SECURITY_SELINUX
	security_secctx_to_secid(ESDFS_LOWER_SECCTX,
				 strlen(ESDFS_LOWER_SECCTX),
				 &sbi->lower_secid);
#endif
	/*
	 * No need to call interpose because we already have a positive
	 * dentry, which was instantiated by d_make_root.  Just need to
	 * d_rehash it.
	 */
	d_rehash(sb->s_root);
	if (!silent)
		esdfs_msg(sb, KERN_INFO, "mounted on top of %s type %s\n",
			dev_name, lower_sb->s_type->name);

	if (!ESDFS_DERIVE_PERMS(sbi))
		goto out;

	/* let user know that we ignore this option in derived mode */
	if (memcmp(&sbi->upper_perms,
		   &esdfs_perms_table[ESDFS_PERMS_UPPER_LEGACY],
		   sizeof(struct esdfs_perms)))
		esdfs_msg(sb, KERN_WARNING, "'upper' mount option ignored in derived mode\n");

	/* all derived modes start with the same, basic root */
	memcpy(&sbi->upper_perms,
	       &esdfs_perms_table[ESDFS_PERMS_UPPER_DERIVED],
	       sizeof(struct esdfs_perms));

	/*
	 * In Android 3.0 all user conent in the emulated storage tree was
	 * stored in /data/media.  Android 4.2 introduced multi-user support,
	 * which required that the primary user's content be migrated from
	 * /data/media to /data/media/0.  The framework then uses bind mounts
	 * to create per-process namespaces to isolate each user's tree at
	 * /data/media/N.  This approach of having each user in a common root
	 * is now considered "legacy" by the sdcard service.
	 */
	if (test_opt(sbi, DERIVE_LEGACY)) {
		ESDFS_I(inode)->tree = ESDFS_TREE_ROOT_LEGACY;
		sbi->obb_parent = dget(sb->s_root);
	/*
	 * Android 4.4 reorganized this sturcture yet again, so that the
	 * primary user's content was again at the root.  Secondary users'
	 * content is found in Android/user/N.  Emulated internal storage still
	 * seems to use the legacy tree, but secondary external storage uses
	 * this method.
	 */
	} else if (test_opt(sbi, DERIVE_UNIFIED))
		ESDFS_I(inode)->tree = ESDFS_TREE_ROOT;
	/*
	 * Later versions of Android organize user content using quantum
	 * entanglement, which has a low probability of being supported by
	 * this driver.
	 */
	else
		esdfs_msg(sb, KERN_WARNING, "unsupported derived permissions mode\n");

	/* initialize root inode */
	esdfs_derive_perms(sb->s_root);

	goto out;

out_freeroot:
	dput(sb->s_root);
out_iput:
	iput(inode);
out_sput:
	/* drop refs we took earlier */
	atomic_dec(&lower_sb->s_active);
out_free:
	kfree(ESDFS_SB(sb));
	sb->s_fs_info = NULL;
out_pput:
	path_put(&lower_path);

out:
	return err;
}

static void*
cifs_dfs_follow_mountpoint(struct dentry *dentry, struct nameidata *nd)
{
	struct dfs_info3_param *referrals = NULL;
	unsigned int num_referrals = 0;
	struct cifs_sb_info *cifs_sb;
	struct cifsSesInfo *ses;
	char *full_path = NULL;
	int xid, i;
	int rc = 0;
	struct vfsmount *mnt = ERR_PTR(-ENOENT);

	cFYI(1, ("in %s", __func__));
	BUG_ON(IS_ROOT(dentry));

	xid = GetXid();

	dput(nd->path.dentry);
	nd->path.dentry = dget(dentry);

	cifs_sb = CIFS_SB(dentry->d_inode->i_sb);
	ses = cifs_sb->tcon->ses;

	if (!ses) {
		rc = -EINVAL;
		goto out_err;
	}

	full_path = build_path_from_dentry(dentry);
	if (full_path == NULL) {
		rc = -ENOMEM;
		goto out_err;
	}

	rc = get_dfs_path(xid, ses , full_path, cifs_sb->local_nls,
		&num_referrals, &referrals,
		cifs_sb->mnt_cifs_flags & CIFS_MOUNT_MAP_SPECIAL_CHR);

	for (i = 0; i < num_referrals; i++) {
		dump_referral(referrals+i);
		/* connect to a storage node */
		if (referrals[i].flags & DFSREF_STORAGE_SERVER) {
			int len;
			len = strlen(referrals[i].node_name);
			if (len < 2) {
				cERROR(1, ("%s: Net Address path too short: %s",
					__func__, referrals[i].node_name));
				rc = -EINVAL;
				goto out_err;
			}
			mnt = cifs_dfs_do_refmount(nd->path.mnt,
						nd->path.dentry,
						referrals + i);
			cFYI(1, ("%s: cifs_dfs_do_refmount:%s , mnt:%p",
					 __func__,
					referrals[i].node_name, mnt));

			/* complete mount procedure if we accured submount */
			if (!IS_ERR(mnt))
				break;
		}
	}

	/* we need it cause for() above could exit without valid submount */
	rc = PTR_ERR(mnt);
	if (IS_ERR(mnt))
		goto out_err;

	nd->path.mnt->mnt_flags |= MNT_SHRINKABLE;
	rc = add_mount_helper(mnt, nd, &cifs_dfs_automount_list);

out:
	FreeXid(xid);
	free_dfs_info_array(referrals, num_referrals);
	kfree(full_path);
	cFYI(1, ("leaving %s" , __func__));
	return ERR_PTR(rc);
out_err:
	path_put(&nd->path);
	goto out;
}

static int do_dentry_open(struct file *f,
			  struct inode *inode,
			  int (*open)(struct inode *, struct file *),
			  const struct cred *cred)
{
	static const struct file_operations empty_fops = {};
	int error;

	f->f_mode = OPEN_FMODE(f->f_flags) | FMODE_LSEEK |
				FMODE_PREAD | FMODE_PWRITE;

	path_get(&f->f_path);
	f->f_inode = inode;
	f->f_mapping = inode->i_mapping;

	if (unlikely(f->f_flags & O_PATH)) {
		f->f_mode = FMODE_PATH;
		f->f_op = &empty_fops;
		return 0;
	}

	if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) {
		error = get_write_access(inode);
		if (unlikely(error))
			goto cleanup_file;
		error = __mnt_want_write(f->f_path.mnt);
		if (unlikely(error)) {
			put_write_access(inode);
			goto cleanup_file;
		}
		f->f_mode |= FMODE_WRITER;
	}

	/* POSIX.1-2008/SUSv4 Section XSI 2.9.7 */
	if (S_ISREG(inode->i_mode))
		f->f_mode |= FMODE_ATOMIC_POS;

	f->f_op = fops_get(inode->i_fop);
	if (unlikely(WARN_ON(!f->f_op))) {
		error = -ENODEV;
		goto cleanup_all;
	}

	error = security_file_open(f, cred);
	if (error)
		goto cleanup_all;

	error = break_lease(inode, f->f_flags);
	if (error)
		goto cleanup_all;

	if (!open)
		open = f->f_op->open;
	if (open) {
		error = open(inode, f);
		if (error)
			goto cleanup_all;
	}
	if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
		i_readcount_inc(inode);
	if ((f->f_mode & FMODE_READ) &&
	     likely(f->f_op->read || f->f_op->read_iter))
		f->f_mode |= FMODE_CAN_READ;
	if ((f->f_mode & FMODE_WRITE) &&
	     likely(f->f_op->write || f->f_op->write_iter))
		f->f_mode |= FMODE_CAN_WRITE;

	f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);

	file_ra_state_init(&f->f_ra, f->f_mapping->host->i_mapping);

	return 0;

cleanup_all:
	fops_put(f->f_op);
	if (f->f_mode & FMODE_WRITER) {
		put_write_access(inode);
		__mnt_drop_write(f->f_path.mnt);
	}
cleanup_file:
	path_put(&f->f_path);
	f->f_path.mnt = NULL;
	f->f_path.dentry = NULL;
	f->f_inode = NULL;
	return error;
}