115 lines
3.1 KiB
Groff
115 lines
3.1 KiB
Groff
.\" Copyright (c) 2014, 2019 The FreeBSD Foundation
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.\"
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.\" Part of this documentation was written by
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.\" Konstantin Belousov <kib@FreeBSD.org> under sponsorship
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.\" from the FreeBSD Foundation.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd April 19, 2019
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.Dt CASU 9
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.Os
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.Sh NAME
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.Nm casueword ,
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.Nm casueword32 ,
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.Nm casuword ,
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.Nm casuword32
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.Nd fetch, compare and store data from user-space
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/systm.h
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.Ft int
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.Fo casueword
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.Fa "volatile u_long *base"
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.Fa "u_long oldval"
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.Fa "u_long *oldvalp"
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.Fa "u_long newval"
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.Fc
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.Ft int
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.Fo casueword32
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.Fa "volatile uint32_t *base"
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.Fa "uint32_t oldval"
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.Fa "uint32_t *oldvalp"
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.Fa "uint32_t newval"
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.Fc
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.Ft u_long
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.Fo casuword
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.Fa "volatile u_long *base"
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.Fa "u_long oldval"
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.Fa "u_long newval"
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.Fc
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.Ft uint32_t
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.Fo casuword32
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.Fa "volatile uint32_t *base"
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.Fa "uint32_t oldval"
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.Fa "uint32_t newval"
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.Fc
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.Sh DESCRIPTION
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The
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.Nm
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functions are designed to perform atomic compare-and-swap operation on
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the value in the usermode memory of the current process.
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.Pp
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The
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.Nm
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routines reads the value from user memory with address
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.Pa base ,
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and compare the value read with
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.Pa oldval .
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If the values are equal,
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.Pa newval
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is written to the
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.Pa *base .
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In case of
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.Fn casueword32
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and
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.Fn casueword ,
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old value is stored into the (kernel-mode) variable pointed by
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.Pa *oldvalp .
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The userspace value must be naturally aligned.
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.Pp
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The callers of
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.Fn casuword
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and
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.Fn casuword32
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functions cannot distinguish between -1 read from
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userspace and function failure.
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.Sh RETURN VALUES
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The
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.Fn casuword
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and
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.Fn casuword32
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functions return the data fetched or -1 on failure.
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The
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.Fn casueword
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and
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.Fn casueword32
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functions return 0 on success, -1 on failure to access memory,
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and 1 when comparison or store failed.
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The store can fail on load-linked/store-conditional architectures.
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.Sh SEE ALSO
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.Xr atomic 9 ,
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.Xr fetch 9 ,
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.Xr store 9
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