C++ retry_estale函数代码示例

SYSCALL_DEFINE3(fchmodat, int, dfd, const char __user *, filename, mode_t, mode)
{
	struct path path;
	struct inode *inode;
	int error;
	struct iattr newattrs;
	unsigned int lookup_flags = LOOKUP_FOLLOW;
retry:
	error = user_path_at(dfd, filename, lookup_flags, &path);
	if (error)
		goto out;
	inode = path.dentry->d_inode;

	error = mnt_want_write(path.mnt);
	if (error)
		goto dput_and_out;
	mutex_lock(&inode->i_mutex);
	if (mode == (mode_t) -1)
		mode = inode->i_mode;
	newattrs.ia_mode = (mode & S_IALLUGO) | (inode->i_mode & ~S_IALLUGO);
	newattrs.ia_valid = ATTR_MODE | ATTR_CTIME;
	error = notify_change(path.dentry, &newattrs);
	mutex_unlock(&inode->i_mutex);
	mnt_drop_write(path.mnt);
dput_and_out:
	path_put(&path);
	if (retry_estale(error, lookup_flags)) {
		lookup_flags |= LOOKUP_REVAL;
		goto retry;
	}
out:
	return error;
}

SYSCALL_DEFINE5(fchownat, int, dfd, const char __user *, filename, uid_t, user,
		gid_t, group, int, flag)
{
	struct path path;
	int error = -EINVAL;
	int lookup_flags;

	if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
		goto out;

	lookup_flags = (flag & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW;
	if (flag & AT_EMPTY_PATH)
		lookup_flags |= LOOKUP_EMPTY;
retry:
	error = user_path_at(dfd, filename, lookup_flags, &path);
	if (error)
		goto out;
	error = mnt_want_write(path.mnt);
	if (error)
		goto out_release;
	error = chown_common(&path, user, group);
	mnt_drop_write(path.mnt);
out_release:
	path_put(&path);
	if (retry_estale(error, lookup_flags)) {
		lookup_flags |= LOOKUP_REVAL;
		goto retry;
	}
out:
	return error;
}

SYSCALL_DEFINE1(chroot, const char __user *, filename)
{
	struct path path;
	int error;
	unsigned int lookup_flags = LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
retry:
	error = user_path_at(AT_FDCWD, filename, lookup_flags, &path);
	if (error)
		goto out;

	error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_CHDIR);
	if (error)
		goto dput_and_out;

	error = -EPERM;
	if (!nsown_capable(CAP_SYS_CHROOT))
		goto dput_and_out;
	error = security_path_chroot(&path);
	if (error)
		goto dput_and_out;

	set_fs_root(current->fs, &path);
	error = 0;
dput_and_out:
	path_put(&path);
	if (retry_estale(error, lookup_flags)) {
		lookup_flags |= LOOKUP_REVAL;
		goto retry;
	}
out:
	return error;
}

SYSCALL_DEFINE1(chdir, const char __user *, filename)
{
	struct path path;
	int error;
	unsigned int lookup_flags = LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
retry:
	error = user_path_at(AT_FDCWD, filename, lookup_flags, &path);
	if (error)
		goto out;

	error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_ACCESS);
	if (error)
		goto dput_and_out;

	set_fs_pwd(current->fs, &path);

dput_and_out:
	path_put(&path);
	if (retry_estale(error, lookup_flags)) {
		lookup_flags |= LOOKUP_REVAL;
		goto retry;
	}
out:
	return error;
}

int vfs_fstatat(int dfd, const char __user *filename, struct kstat *stat,
		int flag)
{
	struct path path;
	int error = -EINVAL;
	unsigned int lookup_flags = 0;

	if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_NO_AUTOMOUNT |
		      AT_EMPTY_PATH)) != 0)
		goto out;

	if (!(flag & AT_SYMLINK_NOFOLLOW))
		lookup_flags |= LOOKUP_FOLLOW;
	if (flag & AT_EMPTY_PATH)
		lookup_flags |= LOOKUP_EMPTY;
retry:
	error = user_path_at(dfd, filename, lookup_flags, &path);
	if (error)
		goto out;

	error = vfs_getattr(&path, stat);
	path_put(&path);
	if (retry_estale(error, lookup_flags)) {
		lookup_flags |= LOOKUP_REVAL;
		goto retry;
	}
out:
	return error;
}

SYSCALL_DEFINE4(readlinkat, int, dfd, const char __user *, pathname,
		char __user *, buf, int, bufsiz)
{
	struct path path;
	int error;
	int empty = 0;
	unsigned int lookup_flags = LOOKUP_EMPTY;

	if (bufsiz <= 0)
		return -EINVAL;

retry:
	error = user_path_at_empty(dfd, pathname, lookup_flags, &path, &empty);
	if (!error) {
		struct inode *inode = d_backing_inode(path.dentry);

		error = empty ? -ENOENT : -EINVAL;
		if (inode->i_op->readlink) {
			error = security_inode_readlink(path.dentry);
			if (!error) {
				touch_atime(&path);
				error = inode->i_op->readlink(path.dentry,
							      buf, bufsiz);
			}
		}
		path_put(&path);
		if (retry_estale(error, lookup_flags)) {
			lookup_flags |= LOOKUP_REVAL;
			goto retry;
		}
	}
	return error;
}

/*
 * do_utimes - change times on filename or file descriptor
 * @dfd: open file descriptor, -1 or AT_FDCWD
 * @filename: path name or NULL
 * @times: new times or NULL
 * @flags: zero or more flags (only AT_SYMLINK_NOFOLLOW for the moment)
 *
 * If filename is NULL and dfd refers to an open file, then operate on
 * the file.  Otherwise look up filename, possibly using dfd as a
 * starting point.
 *
 * If times==NULL, set access and modification to current time,
 * must be owner or have write permission.
 * Else, update from *times, must be owner or super user.
 */
long do_utimes(int dfd, const char __user *filename, struct timespec *times,
	       int flags)
{
	int error = -EINVAL;

	if (times && (!nsec_valid(times[0].tv_nsec) ||
		      !nsec_valid(times[1].tv_nsec))) {
		goto out;
	}

	if (flags & ~AT_SYMLINK_NOFOLLOW)
		goto out;

	if (filename == NULL && dfd != AT_FDCWD) {
		struct fd f;

		if (flags & AT_SYMLINK_NOFOLLOW)
			goto out;

		f = fdget(dfd);
		error = -EBADF;
		if (!f.file)
			goto out;

		error = utimes_common(&f.file->f_path, times);
		fdput(f);
	} else {
		struct path path;
		int lookup_flags = 0;

		if (!(flags & AT_SYMLINK_NOFOLLOW))
			lookup_flags |= LOOKUP_FOLLOW;
retry:
		error = user_path_at(dfd, filename, lookup_flags, &path);
		if (error)
			goto out;

		error = utimes_common(&path, times);
		path_put(&path);
		if (retry_estale(error, lookup_flags)) {
			lookup_flags |= LOOKUP_REVAL;
			goto retry;
		}
	}

out:
	return error;
}

SYSCALL_DEFINE3(fchmodat, int, dfd, const char __user *, filename, umode_t, mode)
{
	struct path path;
	int error;
	unsigned int lookup_flags = LOOKUP_FOLLOW;
retry:
	error = user_path_at(dfd, filename, lookup_flags, &path);
	if (!error) {
		error = chmod_common(&path, mode);
		path_put(&path);
		if (retry_estale(error, lookup_flags)) {
			lookup_flags |= LOOKUP_REVAL;
			goto retry;
		}
	}
	return error;
}

int user_statfs(const char __user *pathname, struct kstatfs *st)
{
	struct path path;
	int error;
	unsigned int lookup_flags = LOOKUP_FOLLOW;
retry:
	error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
	if (!error) {
		error = vfs_statfs(&path, st);
		path_put(&path);
		if (retry_estale(error, lookup_flags)) {
			lookup_flags |= LOOKUP_REVAL;
			goto retry;
		}
	}
	return error;
}

static long do_sys_truncate(const char __user *pathname, loff_t length)
{
	unsigned int lookup_flags = LOOKUP_FOLLOW;
	struct path path;
	int error;

	if (length < 0)	/* sorry, but loff_t says... */
		return -EINVAL;

retry:
	error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
	if (!error) {
		error = vfs_truncate(&path, length);
		path_put(&path);
	}
	if (retry_estale(error, lookup_flags)) {
		lookup_flags |= LOOKUP_REVAL;
		goto retry;
	}
	return error;
}

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;
	unsigned int lookup_flags = LOOKUP_FOLLOW;

	if (mode & ~S_IRWXO)	
		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)) {
		
		kuid_t root_uid = make_kuid(override_cred->user_ns, 0);
		if (!uid_eq(override_cred->uid, root_uid))
			cap_clear(override_cred->cap_effective);
		else
			override_cred->cap_effective =
				override_cred->cap_permitted;
	}

	old_cred = override_creds(override_cred);
retry:
	res = user_path_at(dfd, filename, lookup_flags, &path);
	if (res)
		goto out;

	inode = path.dentry->d_inode;

	if ((mode & MAY_EXEC) && S_ISREG(inode->i_mode)) {
		res = -EACCES;
		if (path.mnt->mnt_flags & MNT_NOEXEC)
			goto out_path_release;
	}

	res = inode_permission(inode, mode | MAY_ACCESS);
	
	if (res || !(mode & S_IWOTH) || special_file(inode->i_mode))
		goto out_path_release;
	if (__mnt_is_readonly(path.mnt))
		res = -EROFS;

out_path_release:
	path_put(&path);
	if (retry_estale(res, lookup_flags)) {
		lookup_flags |= LOOKUP_REVAL;
		goto retry;
	}
out:
	revert_creds(old_cred);
	put_cred(override_cred);
	return res;
}