From mboxrd@z Thu Jan  1 00:00:00 1970
From: Florian Weimer <fweimer@redhat.com>
Subject: Re: [PATCH v3 5/5] selftests: add fchmodat4(2) selftest
Date: Tue, 11 Jul 2023 14:10:58 +0200
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In-Reply-To: <c3606ec38227d921fa8a3e11613ffdb2f3ea7636.1689074739.git.legion@kernel.org>
        (Alexey Gladkov's message of "Tue, 11 Jul 2023 13:25:46 +0200")
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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, 

* 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