Why we need fd transfer instead of just create new listener in new process?

[taikulawo]

From my understand, transfer will send fd to new process, let next process continue to drain connections in that fd's backlog.
but If new process use REUSEPORT and then listen, accept, it still can accept connections from kernel socket addr 4 tuple.

Why we need transfer not create?

[eaufavor]

Good question. Sockets under REUSEPORT have their own listening queues. When closing such a socket (in the old process), all the half-opened TCP connections are dropped. To such connections, the server is offline.

When a listening socket is transferred. It still binds to the same listening queue that old socket binds to. So when the old socket is closed, no connection will be lost.

[github-actions]

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