1.\" Copyright (c) 2014, 2019 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 April 19, 2019 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.Fo casueword 45.Fa "volatile u_long *base" 46.Fa "u_long oldval" 47.Fa "u_long *oldvalp" 48.Fa "u_long newval" 49.Fc 50.Ft int 51.Fo casueword32 52.Fa "volatile uint32_t *base" 53.Fa "uint32_t oldval" 54.Fa "uint32_t *oldvalp" 55.Fa "uint32_t newval" 56.Fc 57.Ft u_long 58.Fo casuword 59.Fa "volatile u_long *base" 60.Fa "u_long oldval" 61.Fa "u_long newval" 62.Fc 63.Ft uint32_t 64.Fo casuword32 65.Fa "volatile uint32_t *base" 66.Fa "uint32_t oldval" 67.Fa "uint32_t newval" 68.Fc 69.Sh DESCRIPTION 70The 71.Nm 72functions are designed to perform atomic compare-and-swap operation on 73the value in the usermode memory of the current process. 74.Pp 75The 76.Nm 77routines reads the value from user memory with address 78.Pa base , 79and compare the value read with 80.Pa oldval . 81If the values are equal, 82.Pa newval 83is written to the 84.Pa *base . 85In case of 86.Fn casueword32 87and 88.Fn casueword , 89old value is stored into the (kernel-mode) variable pointed by 90.Pa *oldvalp . 91The userspace value must be naturally aligned. 92.Pp 93The callers of 94.Fn casuword 95and 96.Fn casuword32 97functions cannot distinguish between -1 read from 98userspace and function failure. 99.Sh RETURN VALUES 100The 101.Fn casuword 102and 103.Fn casuword32 104functions return the data fetched or -1 on failure. 105The 106.Fn casueword 107and 108.Fn casueword32 109functions return 0 on success, -1 on failure to access memory, 110and 1 when comparison or store failed. 111The store can fail on load-linked/store-conditional architectures. 112.Sh SEE ALSO 113.Xr atomic 9 , 114.Xr fetch 9 , 115.Xr store 9 116