Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Florian Weimer <fweimer@redhat.com>
To:     Alexey Gladkov <legion@kernel.org>
Cc:     LKML <linux-kernel@vger.kernel.org>, Arnd Bergmann <arnd@arndb.de>,
        linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        viro@zeniv.linux.org.uk, James.Bottomley@HansenPartnership.com,
        acme@kernel.org, alexander.shishkin@linux.intel.com,
        axboe@kernel.dk, benh@kernel.crashing.org, borntraeger@de.ibm.com,
        bp@alien8.de, catalin.marinas@arm.com, christian@brauner.io,
        dalias@libc.org, davem@davemloft.net, deepa.kernel@gmail.com,
        deller@gmx.de, dhowells@redhat.com, fenghua.yu@intel.com,
        firoz.khan@linaro.org, geert@linux-m68k.org, glebfm@altlinux.org,
        gor@linux.ibm.com, hare@suse.com, heiko.carstens@de.ibm.com,
        hpa@zytor.com, ink@jurassic.park.msu.ru, jhogan@kernel.org,
        kim.phillips@arm.com, ldv@altlinux.org,
        linux-alpha@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org,
        linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org,
        linux-parisc@vger.kernel.org, linux-s390@vger.kernel.org,
        linux-sh@vger.kernel.org, linux@armlinux.org.uk,
        linuxppc-dev@lists.ozlabs.org, luto@kernel.org, mattst88@gmail.com,
        mingo@redhat.com, monstr@monstr.eu, mpe@ellerman.id.au,
        namhyung@kernel.org, palmer@sifive.com, paul.burton@mips.com,
        paulus@samba.org, peterz@infradead.org, ralf@linux-mips.org,
        rth@twiddle.net, schwidefsky@de.ibm.com,
        sparclinux@vger.kernel.org, stefan@agner.ch, tglx@linutronix.de,
        tony.luck@intel.com, tycho@tycho.ws, will@kernel.org,
        x86@kernel.org, ysato@users.sourceforge.jp
Subject: Re: [PATCH v3 5/5] selftests: add fchmodat4(2) selftest
References: <87o8pscpny.fsf@oldenburg2.str.redhat.com>
        <cover.1689074739.git.legion@kernel.org>
        <c3606ec38227d921fa8a3e11613ffdb2f3ea7636.1689074739.git.legion@kernel.org>
Date:   Tue, 11 Jul 2023 14:10:58 +0200
In-Reply-To: <c3606ec38227d921fa8a3e11613ffdb2f3ea7636.1689074739.git.legion@kernel.org>
        (Alexey Gladkov's message of "Tue, 11 Jul 2023 13:25:46 +0200")
Message-ID: <87pm4ybqct.fsf@oldenburg.str.redhat.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

* Alexey Gladkov:

> The test marks as skipped if a syscall with the AT_SYMLINK_NOFOLLOW flag
> fails. This is because not all filesystems support changing the mode
> bits of symlinks properly. These filesystems return an error but change
> the mode bits:
>
> newfstatat(4, "regfile", {st_mode=3DS_IFREG|0640, st_size=3D0, ...}, AT_S=
YMLINK_NOFOLLOW) =3D 0
> newfstatat(4, "symlink", {st_mode=3DS_IFLNK|0777, st_size=3D7, ...}, AT_S=
YMLINK_NOFOLLOW) =3D 0
> syscall_0x1c3(0x4, 0x55fa1f244396, 0x180, 0x100, 0x55fa1f24438e, 0x34) =
=3D -1 EOPNOTSUPP (Operation not supported)
> newfstatat(4, "regfile", {st_mode=3DS_IFREG|0640, st_size=3D0, ...}, AT_S=
YMLINK_NOFOLLOW) =3D 0
>
> This happens with btrfs and xfs:
>
>  $ /kernel/tools/testing/selftests/fchmodat4/fchmodat4_test
>  TAP version 13
>  1..1
>  ok 1 # SKIP fchmodat4(symlink)
>  # Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0
>
>  $ stat /tmp/ksft-fchmodat4.*/symlink
>    File: /tmp/ksft-fchmodat4.3NCqlE/symlink -> regfile
>    Size: 7               Blocks: 0          IO Block: 4096   symbolic link
>  Device: 7,0     Inode: 133         Links: 1
>  Access: (0600/lrw-------)  Uid: (    0/    root)   Gid: (    0/    root)
>
> Signed-off-by: Alexey Gladkov <legion@kernel.org>

This looks like a bug in those file systems?

As an extra test, =E2=80=9Cecho 3 > /proc/sys/vm/drop_caches=E2=80=9D somet=
imes has
strange effects in such cases because the bits are not actually stored
on disk, only in the dentry cache.

Thanks,
Florian