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Date: Wed, 29 Apr 2026 19:48:06 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: achender@kernel.org
Cc: netdev@vger.kernel.org, pabeni@redhat.com, edumazet@google.com,
 horms@kernel.org, linux-rdma@vger.kernel.org,
 linux-kselftest@vger.kernel.org, shuah@kernel.org
Subject: Re: [PATCH net-next v2 5/7] selftests: rds: Fix gcov and pcap
 collection
Message-ID: <20260429194806.6ae176a9@kernel.org>
In-Reply-To: <20260430024206.2452353-1-kuba@kernel.org>
References: <20260428222716.2960871-6-achender@kernel.org>
	<20260430024206.2452353-1-kuba@kernel.org>
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On Wed, 29 Apr 2026 19:42:06 -0700 Jakub Kicinski wrote:
> > +# tcpdump saves pcaps to /tmp because it requires chown to save the
> > +# pcap but chown is not supported by 9p.  Mount tmpfs on /tmp if it is
> > +# not already a separate filesystem
> > +if ! mountpoint -q /tmp 2>/dev/null; then
> > +	mount -t tmpfs tmpfs /tmp
> > +fi
> > +  
> 
> Could this introduce a regression when the test is run directly on a host
> workstation rather than inside an isolated VM?
> 
> If /tmp is a regular directory on the root filesystem, mounting tmpfs over it
> will instantly hide all existing files and UNIX domain sockets in /tmp.
> 
> Since there is no cleanup trap to unmount it on exit or failure, does this
> leave the host system in a degraded state?

I share Sashiko's mixed feelings here. Do other tests mount /tmp ?
Seems like something that belongs in the "CI setup", external
to ksft itself.

point #2 my vng does have an overlayfs mounted over /tmp so the
mountpoint check doesn't trigger IDK if this is what you meant 
or I have a different version.