posix_spawn() is great, but Linux doesn't implement it. glibc does based on fork()+exec(). Other Unix(-like) OSes do implement posix_spawn() as system call. Also while you can use posix_spawn() in the vast majority of cases, if it doesn't cover certain process setup options that you need you still have to use fork()+exec(). But yeah, it would be good if Linux had it as a system call. It would probably help PostgreSQL.
Yes, of course. Did remember its not fork(), but some other *fork() and couldn't remember the name. But just the kind of thing it does. Its also not exec(), but probably execvp() or execvpe() or something like that.
When using vfork() what are you allowed to do? Can you even do IO redirection (piping)? The man page says:
> ... the behavior is undefined if the process created by vfork() either modifies any data other than a variable of type pid_t used to store the return value from vfork() ...
But the time between fork and exec is exactly where you do a lot of setup, like IO redirection, dropping privileges, setuid(), setting a signal mask (nohup) etc. and I don't think you can do that without setting any variables. You certainly write to the stack when calling a function.
If you can't do these things you can't really use it to implement posix_spawn(). I guess it could use vfork() in the case no actions are required, but only then.
