Copyright (c) 2002 The NetBSD Foundation, Inc.
All rights reserved.
This code is derived from software contributed to The NetBSD Foundation
by Gregory McGarry.
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.
3. All advertising materials mentioning features or use of this software
must display the following acknowledgement:
This product includes software developed by the NetBSD
Foundation, Inc. and its contributors.
4. Neither the name of The NetBSD Foundation nor the names of its
contributors may be used to endorse or promote products derived
from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
.Dd August 12, 2002 .Dt RASCTL 2 .Os .Sh NAME .Nm rasctl .Nd restartable atomic sequences .Sh LIBRARY .Lb libc .Sh SYNOPSIS .Fd #include \*[Lt]sys/types.h\*[Gt] .Fd #include \*[Lt]sys/ras.h\*[Gt] .Ft int .Fn rasctl "void *addr" "size_t len" "int op" .Sh DESCRIPTION Restartable atomic sequences are code sequences which are guaranteed to execute without preemption. This property is assured by the kernel by re-executing a preempted sequence from the start. This functionality enables applications to build atomic sequences which, when executed to completion, will have executed atomically. Restartable atomic sequences are intended to be used on systems that do not have hardware support for low-overhead atomic primitives.
p The .Nm function manipulates a process's set of restartable atomic sequences. If a restartable atomic sequence is registered and the process is preempted within the range .Fa addr and .Fa addr Ns + Ns Fa len , then the process is resumed at .Fa addr .
p As the process execution can be rolled-back, the code in the sequence should have no side effects other than a final store at .Fa addr Ns + Ns Fa len Ns -1 . The kernel does not guarantee that the sequences are successfully restartable. It assumes that the application knows what it is doing. Restartable atomic sequences should adhere to the following guidelines:
p l -bullet -compact t have a single entry point and a single exit point; t not execute emulated instructions; and t not invoke any functions or system calls. .El
p Restartable atomic sequences are inherited from the parent by the child during the .Xr fork 2 operation. Restartable atomic sequences for a process are removed during .Xr exec 3 .
p The operations that can be applied to a restartable atomic sequence are specified by the .Fa op argument. Possible operations are:
p l -tag -compact -width RAS_PURGE_ALLXXX t RAS_INSTALL Install this sequence. t RAS_PURGE Remove the specified registered sequences for this process. t RAS_PURGE_ALL Remove all registers sequences for this process. .El
p
To preserve the atomicity of sequences, the kernel attempts to protect
the sequences from alteration by the
.Xr ptrace 2
facility.
.Sh RETURN VALUES
Upon successful completion,
.Fn rasctl
returns zero. Otherwise, -1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Nm
function will fail if:
l -tag -width Er t Bq Er EINVAL Invalid input was supplied, such as an invalid operation, an invalid
address, or an invalid length. A process may have a finite number of
atomic sequences that is defined at compile time.
t Bq Er EOPNOTSUPP Restartable atomic sequences are not supported by the kernel.
t Bq Er ESRCH Restartable atomic sequence not registered.
.El
.Sh SEE ALSO
.Xr ptrace 2
.Xr lock 9
.Sh HISTORY
The
.Nm
functionality first appeared in
.Nx 2.0
based on a similar interface that appeared in Mach 2.5.
Indexes created Thu Oct 02 14:10:14 GMT 2025