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From reading the source code, it appears like the desired semantic of std::unix::rand is to always provide some bytes and never block. For that reason GRND_NONBLOCK is checked before calling getrandom(0), so that getrandom(0) won't block. If it would block, then the function falls back to using /dev/urandom, which for the time being doesn't block. There are some drawbacks to using /dev/urandom, however, and so getrandom(GRND_INSECURE) was created as a replacement for this exact circumstance. getrandom(GRND_INSECURE) is the same as /dev/urandom, except: - It won't leave a warning in dmesg if used at early boot time, which is a common occurance (and the reason why I found this issue); - It won't introduce a tiny delay at early boot on newer kernels when /dev/urandom tries to opportunistically create jitter entropy; - It only requires 1 syscall, rather than 3. Other than that, it returns the same "quality" of randomness as /dev/urandom, and never blocks. It's only available on kernels ≥5.6, so we try to use it, cache the result of that attempt, and fall back to to the previous code if it didn't work. |
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| alloc | ||
| backtrace@b02ed04a7e | ||
| core | ||
| panic_abort | ||
| panic_unwind | ||
| portable-simd | ||
| proc_macro | ||
| profiler_builtins | ||
| rtstartup | ||
| rustc-std-workspace-alloc | ||
| rustc-std-workspace-core | ||
| rustc-std-workspace-std | ||
| std | ||
| stdarch@28335054b1 | ||
| test | ||
| unwind | ||