Function vn_io_fault

freebsd/kern/vfs_vnops.c:1368–1423

}

static int
vn_io_fault(struct file *fp, struct uio *uio, struct ucred *active_cred,
    int flags, struct thread *td)
{
	fo_rdwr_t *doio;
	struct vnode *vp;
	void *rl_cookie;
	struct vn_io_fault_args args;
	int error;

	doio = uio->uio_rw == UIO_READ ? vn_read : vn_write;
	vp = fp->f_vnode;

	/*
	 * The ability to read(2) on a directory has historically been
	 * allowed for all users, but this can and has been the source of
	 * at least one security issue in the past.  As such, it is now hidden
	 * away behind a sysctl for those that actually need it to use it, and
	 * restricted to root when it's turned on to make it relatively safe to
	 * leave on for longer sessions of need.
	 */
	if (vp->v_type == VDIR) {
		KASSERT(uio->uio_rw == UIO_READ,
		    ("illegal write attempted on a directory"));
		if (!vfs_allow_read_dir)
			return (EISDIR);
		if ((error = priv_check(td, PRIV_VFS_READ_DIR)) != 0)
			return (EISDIR);
	}

	foffset_lock_uio(fp, uio, flags);
	if (do_vn_io_fault(vp, uio)) {
		args.kind = VN_IO_FAULT_FOP;
		args.args.fop_args.fp = fp;
		args.args.fop_args.doio = doio;
		args.cred = active_cred;
		args.flags = flags | FOF_OFFSET;
		if (uio->uio_rw == UIO_READ) {
			rl_cookie = vn_rangelock_rlock(vp, uio->uio_offset,
			    uio->uio_offset + uio->uio_resid);
		} else if ((fp->f_flag & O_APPEND) != 0 ||
		    (flags & FOF_OFFSET) == 0) {
			/* For appenders, punt and lock the whole range. */
			rl_cookie = vn_rangelock_wlock(vp, 0, OFF_MAX);
		} else {
			rl_cookie = vn_rangelock_wlock(vp, uio->uio_offset,
			    uio->uio_offset + uio->uio_resid);
		}
		error = vn_io_fault1(vp, uio, &args, td);
		vn_rangelock_unlock(vp, rl_cookie);
	} else {
		error = doio(fp, uio, active_cred, flags | FOF_OFFSET, td);
	}
	foffset_unlock_uio(fp, uio, flags);
	return (error);
}

/*