TCP_DEFER_ACCEPT documentation should be more precise about rounding to retransmits

tcp(7) says:

However, it doesn't say *how* it bounds the attempts. From the kernel code, it appears to round up to the first retransmit time that's larger than the specified bound. Could the manpage please document this?

(Discovered when adding Rust bindings to this, and trying to figure out and document the rounding behavior.)

- Josh Triplett

Hi Josh,

Would you mind sending a patch? (And if appropriate, CC someone.)

Have a lovely night!
Alex

<https://www.alejandro-colomar.es>

Patch attached.

From ad2b798376326d40944f6998270a755f61c57815 Mon Sep 17 00:00:00 2001
Message-ID: <ad2b798376326d40944f6998270a755f61c57815.1776374539.git.josh@joshtriplett.org>
From: Josh Triplett <[email protected]>
Date: Thu, 16 Apr 2026 14:21:34 -0700
Subject: [PATCH] Document TCP_DEFER_ACCEPT rounding

---
 man/man7/tcp.7 | 2 ++
 1 file changed, 2 insertions(+)

index ff46ea7bc..26a99b879 100644
@@ -1091,6 +1091,8 @@ Allow a listener to be awakened only when data arrives on the socket.
 Takes an integer value (seconds), this can
 bound the maximum number of attempts TCP will make to
 complete the connection.
+The kernel will round this value up to the next larger TCP retransmit
+duration.
 .IP
 On a client socket,
 if nonzero,

2.53.0

Hi Josh,

Thanks! I've applied the patch.

Have a lovely night!
Alex

<https://www.alejandro-colomar.es>