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RAS(9) NetBSD Kernel Developer's Manual RAS(9)
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by Kimmo Suominen.
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ras_lookup, ras_fork, ras_purgeall -- restartable atomic sequences
ras_lookup(struct proc *p, void *addr);
ras_fork(struct proc *p1, struct proc *p2);
ras_purgeall(struct proc *p);
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
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 con-
trol block (PCB).
The RAS functionality is provided by a combination of the machine-inde-
pendent routines discussed in this page and a machine-dependent component
in cpu_switchto(9). A port which supports restartable atomic sequences
will define __HAVE_RAS in <machine/types.h> for machine-independent code
to conditionally provide RAS support.
A complicated side-effect of restartable atomic sequences is their inter-
action with the machine-dependent ptrace(2) support. Specifically, sin-
gle-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
The functions which operate on restartable atomic sequences are:
This function searches the registered restartable atomic
sequences for process p which contain the user address addr. If
the address addr is found within a RAS, then the restart address
of the RAS is returned, otherwise -1 is returned.
This function is used to copy all registered restartable atomic
sequences for process p1 to process p2. It is primarily called
from fork1(9) when the sequences are inherited from the parent
by the child.
This function is used to remove all registered restartable
atomic sequences for process p. It is primarily used to remove
all registered restartable atomic sequences for a process during
exec(3) and by rasctl(2).
The RAS framework itself is implemented within the file
sys/kern/kern_ras.c. Data structures and function prototypes for the
framework are located in <sys/ras.h>. Machine-dependent portions are
implemented within cpu_switchto(9) in the machine-dependent file
rasctl(2), cpu_switchto(9), fork1(9)
Gregory McGarry, "An Implementation of User-level Restartable Atomic
Sequences on the NetBSD Operating System", Proceedings of the FREENIX
Track: 2003 USENIX Annual Technical Conference, USENIX Association,
311-322, June 9-14, 2003.
The RAS functionality first appeared in NetBSD 2.0.
NetBSD 9.99 April 17, 2010 NetBSD 9.99