Use posix_spawn instead of vfork + exec #2800
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A tor benchmark run shows no performance difference, as expected: https://github.com/shadow/benchmark-results/tree/master/tor/2023-03-22-T22-09-20 |
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Given that this is a relatively risky change, I'll hold off on merging until after the upcoming stable release. |
stevenengler
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Mar 24, 2023
Bare vfork + exec are tricky to use, since it's easy to accidentally corrupt the parent process's state from the child process. It's also unsupported in Rust (rust-lang/libc#1596). I think we could work around this in Rust by using inline assembly or a C helper function to wrap the fork and exec, but `posix_spawn` basically does that for us already.
* posix_spawn_file_actions_addchdir_np isn't present on older versions of glibc. Work around it by instead setting the working directory in the shim. * Older versions of glibc may use `fork` instead of `vfork` unless we explicitly request `vfork`. I'm not sure whether any of our supported platforms are affected by this or not, but it doesn't hurt to set it explicitly. * Older versions of glibc don't have a feature/hack that lets us use a single call to posix_spawn_file_actions_adddup2 with equal descriptor numbers to clear the O_CLOEXEC attribute. Use two calls to posix_spawn_file_actions_adddup2 instead, with a temporary descriptor number.
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Bare vfork + exec are tricky to use, since it's easy to accidentally corrupt the parent process's state from the child process. It's also unsupported in Rust (rust-lang/libc#1574, rust-lang/libc#1596).
I think we could work around this in Rust by using inline assembly or a C helper function to wrap the fork and exec, but
posix_spawnbasically does that for us already.