1.\" Copyright (c) 2014 The FreeBSD Foundation 2.\" All rights reserved. 3.\" 4.\" Part of this documentation was written by 5.\" Konstantin Belousov <kib@FreeBSD.org> under sponsorship 6.\" from the FreeBSD Foundation. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 17.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND 18.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE 21.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27.\" SUCH DAMAGE. 28.\" 29.\" $FreeBSD$ 30.\" 31.Dd October 21, 2014 32.Dt CASU 9 33.Os 34.Sh NAME 35.Nm casueword , 36.Nm casueword32 , 37.Nm casuword , 38.Nm casuword32 39.Nd fetch, compare and store data from user-space 40.Sh SYNOPSIS 41.In sys/types.h 42.In sys/systm.h 43.Ft int 44.Fn casueword "volatile u_long *base" "u_long oldval" "u_long *oldvalp" "u_long newval" 45.Ft int 46.Fn casueword32 "volatile uint32_t *base" "uint32_t oldval" "uint32_t *oldvalp" "uint32_t newval" 47.Ft u_long 48.Fn casuword "volatile u_long *base" "u_long oldval" "u_long newval" 49.Ft uint32_t 50.Fn casuword32 "volatile uint32_t *base" "uint32_t oldval" "uint32_t newval" 51.Sh DESCRIPTION 52The 53.Nm 54functions are designed to perform atomic compare-and-swap operation on 55the value in the usermode memory of the current process. 56.Pp 57The 58.Nm 59routines reads the value from user memory with address 60.Pa base , 61and compare the value read with 62.Pa oldval . 63If the values are equal, 64.Pa newval 65is written to the 66.Pa *base . 67In case of 68.Fn casueword32 69and 70.Fn casueword , 71old value is stored into the (kernel-mode) variable pointed by 72.Pa *oldvalp . 73The userspace value must be naturally aligned. 74.Pp 75The callers of 76.Fn casuword 77and 78.Fn casuword32 79functions cannot distinguish between -1 read from 80userspace and function failure. 81.Sh RETURN VALUES 82The 83.Fn casuword 84and 85.Fn casuword32 86functions return the data fetched or -1 on failure. 87The 88.Fn casueword 89and 90.Fn casueword32 91functions return 0 on success and -1 on failure. 92.Sh SEE ALSO 93.Xr atomic 9 , 94.Xr fetch 9 , 95.Xr store 9 96