RASCTL(2) | System Calls Manual | RASCTL(2) |
rasctl
—
#include <sys/types.h>
#include <sys/ras.h>
int
rasctl
(void
*addr, size_t len,
int op);
The rasctl
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
addr and
addr+len, then the process is
resumed at addr.
As the process execution can be rolled-back, the code in the sequence should have no side effects other than a final store at addr+len-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:
Restartable atomic sequences are inherited from the parent by the child during the fork(2) operation. Restartable atomic sequences for a process are removed during exec(3).
The operations that can be applied to a restartable atomic sequence are specified by the op argument. Possible operations are:
RAS_INSTALL
RAS_PURGE
RAS_PURGE_ALL
The RAS_PURGE
and
RAS_PURGE_ALL
operations should be considered to
have undefined behaviour if there are any other runnable threads in the
address space which might be executing within the restartable atomic
sequence(s) at the time of the purge. The caller must be responsible for
ensuring that there is some form of coordination with other threads to
prevent unexpected behaviour.
To preserve the atomicity of sequences, the kernel attempts to protect the sequences from alteration by the ptrace(2) facility.
rasctl
() returns zero.
Otherwise, -1 is returned and errno is set to indicate
the error.
rasctl
function will fail if:
EINVAL
]EOPNOTSUPP
]ESRCH
]rasctl
functionality first appeared in
NetBSD 2.0 based on a similar interface that appeared
in Mach 2.5.
RAS
need to be protected against
this. One level of protection is created by compiler dependent instructions,
abstracted from user level code via the following macros:
RAS_DECL(name)
RAS
. The name uniquely identifies the
RAS
.RAS_START(name)
RAS_END(name)
RAS_ADDR(name)
RAS
and is used to
create the first argument to rasctl
.RAS_SIZE(name)
RAS
and is used as second
argument to rasctl
.-fno-reorder-blocks
flag to prevent blocks of code
wrapped with RAS_START
/RAS_END
being moved outside these labels. However, be aware that this may not always
be sufficient to prevent gcc(1)
from generating non-restartable code within the RAS
due to register clobbers. It is, therefore, strongly recommended that
restartable atomic sequences are coded in assembly.
RAS
blocks within assembly code can be specified by
using the following macros:
RAS_START_ASM(name)
RAS_START
but for use in assembly
source code.RAS_END_ASM(name)
RAS_END
but for use in assembly source
code.RAS_START_ASM_HIDDEN(name)
RAS_START_ASM
except that the symbol
will not be placed in the dynamic symbol table.RAS_END_ASM_HIDDEN(name)
RAS_END_ASM
except that the symbol will
not be placed in the dynamic symbol table.April 29, 2008 | NetBSD 9.0 |