netdev - Re: [PATCH net-next v2] selftests: tls: use mkstemp instead of open(O

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Message-ID: <66b44ded1d5174131e90fae85b296ef89a53ab24.camel@kernel.org>
Date: Mon, 19 Jan 2026 14:16:32 +0800
From: Geliang Tang <geliang@...nel.org>
To: Jakub Kicinski <kuba@...nel.org>, "Matthieu Baerts (NGI0)"
	 <matttbe@...nel.org>
Cc: John Fastabend <john.fastabend@...il.com>, Sabrina Dubroca	
 <sd@...asysnail.net>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Simon Horman	
 <horms@...nel.org>, Shuah Khan <shuah@...nel.org>, Gang Yan
 <yangang@...inos.cn>, 	netdev@...r.kernel.org,
 linux-kselftest@...r.kernel.org, mptcp@...ts.linux.dev
Subject: Re: [PATCH net-next v2] selftests: tls: use mkstemp instead of
 open(O_TMPFILE)

Hi Jakub, Matt,

On Thu, 2026-01-15 at 18:49 -0800, Jakub Kicinski wrote:
> On Thu, 15 Jan 2026 17:02:40 +0800 Geliang Tang wrote:
> > This is because the /tmp directory uses the virtiofs filesystem,
> > which does
> > not support the O_TMPFILE feature.
> 
> I don't think selftests are expected to support setups where /tmp 
> isn't tmp. Please fix your setup instead (or explain why it's very

Thanks for reviewing. I recently implemented TLS support for MPTCP and
have been adding MPTCP test items to the TLS selftests. When running
these in the MPTCP upstream CI (mptcp-upstream-virtme-docker), these
O_TMPFILE unsupported errors occurred.

Following your suggestion, I looked into the mptcp-upstream-virtme-
docker configuration and found that /tmp isn't mounted as tmpfs; it's
just a plain directory. I've opened a PR to address this:

virtme: mount /tmp as overlay for O_TMPFILE support

https://github.com/multipath-tcp/mptcp-upstream-virtme-docker/pull/43

@Matt

This change adds "--overlay-rwdir /tmp" to virtme-run options, ensuring
/tmp gets mounted as an overlay filesystem. It functions correctly,
though I'm not certain it's the ideal solution.

Thanks,
-Geliang

> crucial that you don't). The upstream CI runs all the selftests in
> VMs and they are working just fine.