casuword.9 revision 274648
Copyright (c) 2014 The FreeBSD Foundation
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Part of this documentation was written by
Konstantin Belousov <kib@FreeBSD.org> under sponsorship
from the FreeBSD Foundation.
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$FreeBSD: stable/10/share/man/man9/casuword.9 274648 2014-11-18 12:53:32Z kib $
.Dd October 21, 2014 .Dt CASU 9 .Os .Sh NAME .Nm casueword , .Nm casueword32 , .Nm casuword , .Nm casuword32 .Nd fetch, compare and store data from user-space .Sh SYNOPSIS n sys/types.h n sys/systm.h .Ft int .Fn casueword "volatile u_long *base" "u_long oldval" "u_long *oldvalp" "u_long newval" .Ft int .Fn casueword32 "volatile uint32_t *base" "uint32_t oldval" "uint32_t *oldvalp" "uint32_t newval" .Ft u_long .Fn casuword "volatile u_long *base" "u_long oldval" "u_long newval" .Ft uint32_t .Fn casuword32 "volatile uint32_t *base" "uint32_t oldval" "uint32_t newval" .Sh DESCRIPTION The .Nm functions are designed to perform atomic compare-and-swap operation on the value in the usermode memory of the current process.
All rights reserved.
Part of this documentation was written by
Konstantin Belousov <kib@FreeBSD.org> under sponsorship
from the FreeBSD Foundation.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.
$FreeBSD: stable/10/share/man/man9/casuword.9 274648 2014-11-18 12:53:32Z kib $
.Dd October 21, 2014 .Dt CASU 9 .Os .Sh NAME .Nm casueword , .Nm casueword32 , .Nm casuword , .Nm casuword32 .Nd fetch, compare and store data from user-space .Sh SYNOPSIS n sys/types.h n sys/systm.h .Ft int .Fn casueword "volatile u_long *base" "u_long oldval" "u_long *oldvalp" "u_long newval" .Ft int .Fn casueword32 "volatile uint32_t *base" "uint32_t oldval" "uint32_t *oldvalp" "uint32_t newval" .Ft u_long .Fn casuword "volatile u_long *base" "u_long oldval" "u_long newval" .Ft uint32_t .Fn casuword32 "volatile uint32_t *base" "uint32_t oldval" "uint32_t newval" .Sh DESCRIPTION The .Nm functions are designed to perform atomic compare-and-swap operation on the value in the usermode memory of the current process.
p The .Nm routines reads the value from user memory with address
a base , and compare the value read with
a oldval . If the values are equal,
a newval is written to the
a *base . In case of .Fn casueword32 and .Fn casueword , old value is stored into the (kernel-mode) variable pointed by
a *oldvalp . The userspace value must be naturally aligned.
p The callers of .Fn casuword and .Fn casuword32 functions cannot distinguish between -1 read from userspace and function failure. .Sh RETURN VALUES The .Fn casuword and .Fn casuword32 functions return the data fetched or -1 on failure. The .Fn casueword and .Fn casueword32 functions return 0 on success and -1 on failure. .Sh SEE ALSO .Xr atomic 9 , .Xr fetch 9 , .Xr store 9