linux-kernel - Re: [PATCH] nvme: Use non zero KATO for persistent discovery connections

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Message-ID: <2841bd1b7910bd0e1b263b393152f2cb13dd3ae3.camel@gmail.com>
Date: Tue, 02 Sep 2025 16:05:19 +0530
From: Martin George <martinus.gpy@...il.com>
To: alistair23@...il.com, kbusch@...nel.org, axboe@...nel.dk, hch@....de, 
	sagi@...mberg.me, linux-nvme@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org, Alistair Francis <alistair.francis@....com>
Subject: Re: [PATCH] nvme: Use non zero KATO for persistent discovery
 connections

On Tue, 2025-09-02 at 13:52 +1000, alistair23@...il.com wrote:
> From: Alistair Francis <alistair.francis@....com>
> 
> The NVMe Base Specification 2.1 states that:
> 
> """
> A host requests an explicit persistent connection ... by specifying a
> non-zero Keep Alive Timer value in the Connect command.
> """
> 
> As such if we are starting a persistent connection to a discovery
> controller and the KATO is currently 0 we need to update KATO to a
> non
> zero value to avoid continuous timeouts on the target.
> 
> 

When would this ever happen? Won't nvme-cli & nvme/host/fabrics.c in
the kernel ensure a PDC (persistent discovery controller) would always
have the KATO either default set to NVMF_DEF_DISC_TMO (i.e. 30s) or any
positive int value & not zero?

Do you have a test log for the above scenario where the KATO ends up
being zero for a PDC?

-Martin