Re: [PATCH 2/6] net: Add CONFIG_LEGACY_IP option

bot+bpf-ci
2026-04-01T09:01:23Z

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> This is the first step toward making Legacy IP optional. The option
> defaults to y and currently has no effect — subsequent patches will use
> it to guard IPv4 entry points.

The commit message says "The option defaults to y", but the Kconfig
entry has no "default y" line. A bool without an explicit default
is n in Kconfig, so LEGACY_IP will be disabled on any fresh config
built with make defconfig or make olddefconfig.

Later patches in this series (be2f051150f9, f04a0717c27d) add
"depends on LEGACY_IP" to all IPv4-specific Kconfig symbols and guard
IPv4 entry points in C code. With LEGACY_IP defaulting to n, those
patches will silently disable IPv4 networking for any newly generated
kernel configuration.

Should the Kconfig entry include "default y" to match the stated
intent?

> diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
> index df922f9f5289..aef2c5349e62 100644
> --- a/net/ipv4/Kconfig
> +++ b/net/ipv4/Kconfig
> @@ -2,6 +2,17 @@
> #
> # IP configuration
> #
> +config LEGACY_IP
> + bool "The IPv4 protocol (Legacy IP)"
> + help
> + Support for IP version 4 (IPv4).
> +
> + Legacy IP is the protocol used by the early ARPANET, before IPv6
> + was standardised in the final decade of the 1900s. It should only
> + be necessary these days to interoperate with legacy networks.
> +
> + If unsure, say N.

The help text says "If unsure, say N." Combined with the missing
default, this guides users to disable IPv4. If the intent is a
backward-compatible introduction where IPv4 stays enabled unless
explicitly turned off, this should probably be "If unsure, say Y."

---
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CI run summary: https://github.com/kernel-patches/bpf/actions/runs/23838411859