is fork() supported?

[DJ Delorie]

I don't mean fork/exec (duh) but a fork() and keep going...

Consider a case where a process is using a file-backed mapping for
closures; a fork() doesn't isolate that backing between parent/child
so there's a chance (for example) the parent could deallocate a
closure that the child needs, etc...

I see four options...

1. Not supported.  Sorry.

2. Supported only if you have fork-able closure backings (mmap or
   maybe ktmpfile, but not file-backed) but this means documenting
   that (at least) selinux settings might affect this.  Caveat
   Programmer.

3. Some API that says "I need this" so it can fail in a more useful
   way than "segfault".

4. Fully supported, and we have some work to do to handle fork events.

Comments?

DJ