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Windows solves this by adding a bunch of optional parameters to CreateProcess, as well as having two more variants (CreateProcessAsUser and CreateProcessWithLogon). Some of the arguments are complicated enough that they have helper functions to construct them.

I like the more composable fork()->modify->exec() approach of unix, but I wouldn't call either of them really elegant.

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That's one option, yes.

The one I've favored while reading these arguments has been the "suspended process" model. The primitives are CREATE(), which takes an executable as a parameter and returns the PID of a paused process, and START(), which allows the process to actually run.

Unix already has the concept of a paused executable, after all.

This model also requires all the process-mutation syscalls, like setrlimit(), to accept a PID as a parameter, but prlimit() wound up being created anyway, because the ability to mutate an already-running process is useful.

A third way is to grant the parent process access to the child such that they can use the child process handle to "remotely" set restrictions, write memory, start a thread, etc.

Practically, syscall overhead has gotten in the way of that being the ubiquitous in the past. Here's to hoping that newer models of syscalls that reduce kernel/user overhead make such a thing possible.

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