linux-kernel - Re: [PATCH v2 8/9] selftests/mm: Skip map

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Message-ID: <CA+i-1C3SYay4WqhGUG1nDpVZT-FRDSzgLHEbH1ONQygjYJS9GQ@mail.gmail.com>
Date: Thu, 27 Feb 2025 13:58:26 +0100
From: Brendan Jackman <jackmanb@...gle.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Shuah Khan <shuah@...nel.org>
Cc: Dev Jain <dev.jain@....com>, linux-mm@...ck.org, linux-kselftest@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 8/9] selftests/mm: Skip map_populate on weird filesystems

On Mon, 24 Feb 2025 at 11:25, Brendan Jackman <jackmanb@...gle.com> wrote:
>
> On Fri, 21 Feb 2025 at 19:26, Brendan Jackman <jackmanb@...gle.com> wrote:
> >
> > It seems that 9pfs does not allow truncating unlinked files, Mark Brown
> > has noted that NFS may also behave this way.
>
> I have not investigated at all but I _think_ over the weekend I saw
> ftruncate() failure on a QEMU guest where /tmp was tmpfs.
>
> Most likely explanation is user probably error (like /tmp wasn't
> actually tmpfs or the tmpfile() did not actually come from /tmp).

OK I double checked. It was in fact a 9p filesystem, turns out
virtme-ng uses that unconditionally for its --rwdir/--rodir mounts
even if the root is virtiofsd, and the tests operate on files in the
CWD as well as in /tmp.

I am still pondering ways to tackle this kinda problem more
systematically but for now I think just skipping these tests is fine.

> +               ksft_exit_skip("ftruncate(fileno(tmpfile())) gave ENOENT, weird filesystem?");

This is missing a newline though, ditto in the subsequent patch. I
will wait and see if any reviews come in before I send a fixup.