1.\" $NetBSD: ucas.9,v 1.2 2011/10/27 07:23:23 wiz Exp $ 2.\" 3.\" Copyright (c)2011 YAMAMOTO Takashi, 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25.\" SUCH DAMAGE. 26.\" 27.\" ------------------------------------------------------------ 28.Dd October 24, 2011 29.Dt UCAS 9 30.Os 31.\" ------------------------------------------------------------ 32.Sh NAME 33.Nm ucas 34.Nd atomic memory operations on user-space address 35.\" ------------------------------------------------------------ 36.Sh SYNOPSIS 37.In sys/systm.h 38.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 39.Ft int 40.Fn ucas_ptr \ 41"volatile void *uptr" "void *old" "void *new" "void *retp" 42.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 43.Ft int 44.Fn ucas_int \ 45"volatile int *uptr" "int old" "int new" "int *retp" 46.\" ------------------------------------------------------------ 47.Sh DESCRIPTION 48These functions provide compare-and-swap (CAS) functionality on 49user-space address. 50.Pp 51Except that they can be safely used for the kernel to access user-space 52address, they are semantically equivalents of 53.Xr atomic_cas 3 . 54.Pp 55.Bl -tag -width uptr 56.It Fa uptr 57The pointer to the variable. 58This should be a user-space pointer. 59.It Fa old 60The value to compare with the variable. 61.It Fa new 62The value to store to the variable. 63.It Fa retp 64The pointer to the memory to store the old value of the variable. 65.El 66.\" ------------------------------------------------------------ 67.Sh RETURN VALUES 68On success, these functions return 0. 69In that case, the caller can consult the value returned via 70.Fa retp 71to check the result of the CAS operation. 72Otherwise, these functions return an appropriate 73.Xr errno 9 74error code, typically 75.Dv EFAULT . 76.\" ------------------------------------------------------------ 77.Sh SEE ALSO 78.Xr atomic_cas 3 , 79.Xr intro 9 80.\" ------------------------------------------------------------ 81.Sh BUGS 82Conceptually, the 83.Fa retp 84argument of 85.Fn ucas_ptr 86would be of 87.Dv void ** . 88The current prototype is a compromise for usability. 89