Re: [OT] 'volatile' in userspace

[Nick Piggin <nickpiggin@yahoo.com.au>]

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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