linux-kernel - Re: [PATCH] debugfs: ignore auto and noauto options if given

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Date: Wed, 29 May 2024 17:33:00 -0500
From: Eric Sandeen <sandeen@...deen.net>
To: Wolfram Sang <wsa+renesas@...g-engineering.com>,
 Christian Brauner <brauner@...nel.org>, Eric Sandeen <sandeen@...hat.com>,
 linux-renesas-soc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>, David Howells
 <dhowells@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] debugfs: ignore auto and noauto options if given

On 5/29/24 5:05 PM, Wolfram Sang wrote:
> Hi Eric,
> 
> thanks for replying!
> 
>> @Wolfram, what did your actual fstab line look like? I wonder what is actually
>> trying to pass auto as a mount option, and why...
> 
> My fstab entry looks like this:
> 
> debugfs /sys/kernel/debug       debugfs auto            0       0
> 
> This happened on an embedded system using busybox 1.33.0. strace is
> currently not installed but I can try adding it if that is needed.
> 
> Happy hacking,
> 
>    Wolfram
> 

Welp, that looks like it:

# strace busybox mount /debugfs-test
..
stat("debugfs", 0x7fffc05d3d60)         = -1 ENOENT (No such file or directory)
mount("debugfs", "/debugfs-test", "debugfs", MS_SILENT, "auto") = -1 EINVAL (Invalid argument)
write(2, "mount: mounting debugfs on /debu"..., 66mount: mounting debugfs on /debugfs-test failed: Invalid argument
) = 66

This does not appear to be unique to debugfs:

# grep tmp /etc/fstab 
/dev/loop0	/tmp/xfs	xfs	auto 0 0
# strace busybox mount /tmp/xfs
..
mount("/dev/loop0", "/tmp/xfs", "xfs", MS_SILENT, "auto") = -1 EINVAL (Invalid argument)
write(2, "mount: mounting /dev/loop0 on /t"..., 64mount: mounting /dev/loop0 on /tmp/xfs failed: Invalid argument
) = 64

# dmesg | grep auto | tail -n 1
[ 1931.471667] xfs: Unknown parameter 'auto'

This looks to me like a busybox flaw, not a debugfs bug (change in unknown
argument behavior notwithstanding...)

-Eric