.\"     $NetBSD: ras.9,v 1.16 2017/07/03 21:28:48 wiz Exp $
.\"
.\" Copyright (c) 2002 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Gregory McGarry.
.\"
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.\" modification, are permitted provided that the following conditions
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.Dd April 17, 2010
.Dt RAS 9
.Os
.Sh NAME
.Nm ras_lookup ,
.Nm ras_fork ,
.Nm ras_purgeall
.Nd restartable atomic sequences
.Sh SYNOPSIS
.In sys/types.h
.In sys/proc.h
.In sys/ras.h
.Ft void *
.Fn ras_lookup "struct proc *p" "void *addr"
.Ft int
.Fn ras_fork "struct proc *p1" "struct proc *p2"
.Ft int
.Fn ras_purgeall "struct proc *p"
.Sh DESCRIPTION
Restartable atomic sequences are user code sequences which are
guaranteed to execute without preemption.
This property is assured by checking the set of restartable atomic
sequences registered for a process during
.Xr cpu_switchto 9 .
If a process is found to have been preempted during a restartable
sequence, then its execution is rolled-back to the start of the
sequence by resetting its program counter saved in its process control block
.Pq Tn PCB .
.Pp
The
.Tn RAS
functionality is provided by a combination of the
machine-independent routines discussed in this page and
a machine-dependent component in
.Xr cpu_switchto 9 .
A port which supports restartable atomic sequences will define
.Dv __HAVE_RAS
in
.In machine/types.h
for machine-independent code to conditionally provide RAS support.
.Pp
A complicated side-effect of restartable atomic sequences is their
interaction with the machine-dependent
.Xr ptrace 2
support.
Specifically, single-step traps and/or the emulation of single-stepping
must carefully consider the effect on restartable atomic sequences.
A general solution is to ignore these traps or disable them within
restartable atomic sequences.
.Sh FUNCTIONS
The functions which operate on restartable atomic sequences are:
.Pp
.Bl -tag -width compact
.It Fn ras_lookup "p" "addr"
This function searches the registered restartable atomic sequences for
process
.Fa p
which contain the user address
.Fa addr .
If the address
.Fa addr
is found within a
.Tn RAS ,
then the restart address of the
.Tn RAS
is returned, otherwise \-1 is returned.
.It Fn ras_fork "p1" "p2"
This function is used to copy all registered restartable atomic
sequences for process
.Fa p1
to process
.Fa p2 .
It is primarily called from
.Xr fork1 9
when the sequences are inherited from the parent by the child.
.It Fn ras_purgeall "p"
This function is used to remove all registered restartable atomic
sequences for process
.Fa p .
It is primarily used to remove all registered restartable atomic
sequences for a process during
.Xr exec 3
and by
.Xr rasctl 2 .
.El
.Sh CODE REFERENCES
The RAS framework itself is implemented within the file
.Pa sys/kern/kern_ras.c .
Data structures and function prototypes for the framework are located
in
.In sys/ras.h .
Machine-dependent portions are implemented within
.Xr cpu_switchto 9
in the machine-dependent file
.Pa sys/arch/<arch>/<arch>/locore.S .
.Sh SEE ALSO
.Xr rasctl 2 ,
.Xr cpu_switchto 9 ,
.Xr fork1 9
.Rs
.%A Gregory McGarry
.%T "An Implementation of User-level Restartable \
Atomic Sequences on the NetBSD Operating System"
.%I USENIX Association
.%B Proceedings of the FREENIX Track: 2003 USENIX Annual Technical Conference
.%P 311-322
.%D June 9-14, 2003
.%U http://www.usenix.org/publications/library/proceedings/usenix03/tech/freenix03/full_papers/mcgarry/mcgarry.pdf
.Re
.Sh HISTORY
The RAS functionality first appeared in
.Nx 2.0 .