Re: [OT] 'volatile' in userspace

From: Nick Piggin
Date: Mon Jul 10 2006 - 18:21:36 EST


Joshua Hudson wrote:

So this would tend to confirm the rule of thumb: use of "volatile" in
a userspace progam tends to indicate a bug.

- Ted


No. vfork(), setjmp(), signal().

Yes, I use vfork. So far, the only way I have found for the parent to
know whether or not the child's exec() failed is this way:

volatile int failed;
pid_t pid;

failed = 0;
if (0 == (pid = vfork())) {
execve(argv[0], argv, envp);
failed = errno;
_exit(0);
}
if (pid < 0) {
/* can't fork */
}
if (failed) {
/* wait for pid (clean up zombie) */
errno = failed;
/* can't exec: update state */
}

May not be portable because you're apparently not supposed to assume
anything about the memory sharing semantics (eg. it may share memory
or it may not -- AFAIK if your code doesn't work correctly after
replacing vfork with fork, then it is buggy).

What's wrong with _exit(exec() == -1 ? 0 : errno);
and picking up the status with wait(2) ?

--
SUSE Labs, Novell Inc.
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