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> Why did Wireguard require so much of its code to be put into the Linux kernel? It didn't require it. Android has a VPN service API for implementing userspace VPNs and there's an official WireGuard app with a userspace implementation. The kernel module isn't a mandatory thing.

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Userspace VPN implementations require a lot of expensive context switches, reducing performance and battery life. It also requires userspace infrastructure / plumbing. Android has support for this including a toggle for always-on and another toggle to block leaks if it dies, etc.

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It is upstream already: the Android Open Source Project. Linux is a kernel and doesn't include userspace. Linux distributions don't share userspace infrastructure. It varies across them. When people want code shipped across them, it has to go into the kernel, since that's Linux.

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Linux isn't like the BSDs, where the kernel and userspace are developed together by the same project. Linux is only a kernel. The only project with the ambition to make shared userspace infrastructure is systemd, but it's the minority and has serious design/implementation flaws.

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AOSP is never going to use systemd, and neither are a lot of embedded, server and container distributions. It's only the majority for desktop Linux, and it's hardly universal there. It has ambition to be universal, shared infrastructure for Linux but it's never going to be that.

3:47 PM · Apr 24, 2020Twitter Web App

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A close cousin from the performance angle is kernel.org/doc/html/lates. The kernel TLS implementation is only the record layer with a single cipher (AES_GCM_128). It makes splice (including sendfile) work for TLS. Linux takes the path of ever increasing features and attack surface.

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The kernel ABI is a public ABI where everything must be stable and backwards compatible forever, since it isn't developed with a specific userspace. Mistakes can't be corrected. There will always be more features, and things will start depending on them making them less optional.

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