Received-SPF: pass (google.com: domain of linux-ext4-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] fs: i_version mntopt gets visible through /proc/mounts
To:     "Darrick J. Wong" <darrick.wong@oracle.com>
Cc:     "J. Bruce Fields" <bfields@fieldses.org>,
        Christoph Hellwig <hch@infradead.org>,
        Masayoshi Mizuma <msys.mizuma@gmail.com>,
        Theodore Ts'o <tytso@mit.edu>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>,
        linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-xfs <linux-xfs@vger.kernel.org>
References: <20200616202123.12656-1-msys.mizuma@gmail.com>
 <20200617080314.GA7147@infradead.org> <20200617155836.GD13815@fieldses.org>
 <24692989-2ee0-3dcc-16d8-aa436114f5fb@sandeen.net>
 <20200617172456.GP11245@magnolia>
From:   Eric Sandeen <sandeen@sandeen.net>
Autocrypt: addr=sandeen@sandeen.net; prefer-encrypt=mutual; keydata=
 mQINBE6x99QBEADMR+yNFBc1Y5avoUhzI/sdR9ANwznsNpiCtZlaO4pIWvqQJCjBzp96cpCs
 nQZV32nqJBYnDpBDITBqTa/EF+IrHx8gKq8TaSBLHUq2ju2gJJLfBoL7V3807PQcI18YzkF+
 WL05ODFQ2cemDhx5uLghHEeOxuGj+1AI+kh/FCzMedHc6k87Yu2ZuaWF+Gh1W2ix6hikRJmQ
 vj5BEeAx7xKkyBhzdbNIbbjV/iGi9b26B/dNcyd5w2My2gxMtxaiP7q5b6GM2rsQklHP8FtW
 ZiYO7jsg/qIppR1C6Zr5jK1GQlMUIclYFeBbKggJ9mSwXJH7MIftilGQ8KDvNuV5AbkronGC
 sEEHj2khs7GfVv4pmUUHf1MRIvV0x3WJkpmhuZaYg8AdJlyGKgp+TQ7B+wCjNTdVqMI1vDk2
 BS6Rg851ay7AypbCPx2w4d8jIkQEgNjACHVDU89PNKAjScK1aTnW+HNUqg9BliCvuX5g4z2j
 gJBs57loTWAGe2Ve3cMy3VoQ40Wt3yKK0Eno8jfgzgb48wyycINZgnseMRhxc2c8hd51tftK
 LKhPj4c7uqjnBjrgOVaVBupGUmvLiePlnW56zJZ51BR5igWnILeOJ1ZIcf7KsaHyE6B1mG+X
 dmYtjDhjf3NAcoBWJuj8euxMB6TcQN2MrSXy5wSKaw40evooGwARAQABtCVFcmljIFIuIFNh
 bmRlZW4gPHNhbmRlZW5Ac2FuZGVlbi5uZXQ+iQI7BBMBAgAlAhsDBgsJCAcDAgYVCAIJCgsE
 FgIDAQIeAQIXgAUCUzMzbAIZAQAKCRAgrhaS4T3e4Fr7D/wO+fenqVvHjq21SCjDCrt8HdVj
 aJ28B1SqSU2toxyg5I160GllAxEHpLFGdbFAhQfBtnmlY9eMjwmJb0sCIrkrB6XNPSPA/B2B
 UPISh0z2odJv35/euJF71qIFgWzp2czJHkHWwVZaZpMWWNvsLIroXoR+uA9c2V1hQFVAJZyk
 EE4xzfm1+oVtjIC12B9tTCuS00pY3AUy21yzNowT6SSk7HAzmtG/PJ/uSB5wEkwldB6jVs2A
 sjOg1wMwVvh/JHilsQg4HSmDfObmZj1d0RWlMWcUE7csRnCE0ZWBMp/ttTn+oosioGa09HAS
 9jAnauznmYg43oQ5Akd8iQRxz5I58F/+JsdKvWiyrPDfYZtFS+UIgWD7x+mHBZ53Qjazszox
 gjwO9ehZpwUQxBm4I0lPDAKw3HJA+GwwiubTSlq5PS3P7QoCjaV8llH1bNFZMz2o8wPANiDx
 5FHgpRVgwLHakoCU1Gc+LXHXBzDXt7Cj02WYHdFzMm2hXaslRdhNGowLo1SXZFXa41KGTlNe
 4di53y9CK5ynV0z+YUa+5LR6RdHrHtgywdKnjeWdqhoVpsWIeORtwWGX8evNOiKJ7j0RsHha
 WrePTubr5nuYTDsQqgc2r4aBIOpeSRR2brlT/UE3wGgy9LY78L4EwPR0MzzecfE1Ws60iSqw
 Pu3vhb7h3bkCDQROsffUARAA0DrUifTrXQzqxO8aiQOC5p9Tz25Np/Tfpv1rofOwL8VPBMvJ
 X4P5l1V2yd70MZRUVgjmCydEyxLJ6G2YyHO2IZTEajUY0Up+b3ErOpLpZwhvgWatjifpj6bB
 SKuDXeThqFdkphF5kAmgfVAIkan5SxWK3+S0V2F/oxstIViBhMhDwI6XsRlnVBoLLYcEilxA
 2FlRUS7MOZGmRJkRtdGD5koVZSM6xVZQSmfEBaYQ/WJBGJQdPy94nnlAVn3lH3+N7pXvNUuC
 GV+t4YUt3tLcRuIpYBCOWlc7bpgeCps5Xa0dIZgJ8Louu6OBJ5vVXjPxTlkFdT0S0/uerCG5
 1u8p6sGRLnUeAUGkQfIUqGUjW2rHaXgWNvzOV6i3tf9YaiXKl3avFaNW1kKBs0T5M1cnlWZU
 Utl6k04lz5OjoNY9J/bGyV3DSlkblXRMK87iLYQSrcV6cFz9PRl4vW1LGff3xRQHngeN5fPx
 ze8X5NE3hb+SSwyMSEqJxhVTXJVfQWWW0dQxP7HNwqmOWYF/6m+1gK/Y2gY3jAQnsWTru4RV
 TZGnKwEPmOCpSUvsTRXsVHgsWJ70qd0yOSjWuiv4b8vmD3+QFgyvCBxPMdP3xsxN5etheLMO
 gRwWpLn6yNFq/xtgs+ECgG+gR78yXQyA7iCs5tFs2OrMqV5juSMGmn0kxJUAEQEAAYkCHwQY
 AQIACQUCTrH31AIbDAAKCRAgrhaS4T3e4BKwD/0ZOOmUNOZCSOLAMjZx3mtYtjYgfUNKi0ki
 YPveGoRWTqbis8UitPtNrG4XxgzLOijSdOEzQwkdOIp/QnZhGNssMejCnsluK0GQd+RkFVWN
 mcQT78hBeGcnEMAXZKq7bkIKzvc06GFmkMbX/gAl6DiNGv0UNAX+5FYh+ucCJZSyAp3sA+9/
 LKjxnTedX0aygXA6rkpX0Y0FvN/9dfm47+LGq7WAqBOyYTU3E6/+Z72bZoG/cG7ANLxcPool
 LOrU43oqFnD8QwcN56y4VfFj3/jDF2MX3xu4v2OjglVjMEYHTCxP3mpxesGHuqOit/FR+mF0
 MP9JGfj6x+bj/9JMBtCW1bY/aPeMdPGTJvXjGtOVYblGZrSjXRn5++Uuy36CvkcrjuziSDG+
 JEexGxczWwN4mrOQWhMT5Jyb+18CO+CWxJfHaYXiLEW7dI1AynL4jjn4W0MSiXpWDUw+fsBO
 Pk6ah10C4+R1Jc7dyUsKksMfvvhRX1hTIXhth85H16706bneTayZBhlZ/hK18uqTX+s0onG/
 m1F3vYvdlE4p2ts1mmixMF7KajN9/E5RQtiSArvKTbfsB6Two4MthIuLuf+M0mI4gPl9SPlf
 fWCYVPhaU9o83y1KFbD/+lh1pjP7bEu/YudBvz7F2Myjh4/9GUAijrCTNeDTDAgvIJDjXuLX pA==
Message-ID: <8f0df756-4f71-9d96-7a52-45bf51482556@sandeen.net>
Date:   Wed, 17 Jun 2020 12:55:24 -0500
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0)
 Gecko/20100101 Thunderbird/68.9.0
MIME-Version: 1.0
In-Reply-To: <20200617172456.GP11245@magnolia>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Sender: linux-ext4-owner@vger.kernel.org
Precedence: bulk

On 6/17/20 12:24 PM, Darrick J. Wong wrote:
> On Wed, Jun 17, 2020 at 12:14:28PM -0500, Eric Sandeen wrote:
>>
>>
>> On 6/17/20 10:58 AM, J. Bruce Fields wrote:
>>> On Wed, Jun 17, 2020 at 01:03:14AM -0700, Christoph Hellwig wrote:
>>>> On Tue, Jun 16, 2020 at 04:21:23PM -0400, Masayoshi Mizuma wrote:
>>>>> From: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
>>>>>
>>>>> /proc/mounts doesn't show 'i_version' even if iversion
>>>>> mount option is set to XFS.
>>>>>
>>>>> iversion mount option is a VFS option, not ext4 specific option.
>>>>> Move the handler to show_sb_opts() so that /proc/mounts can show
>>>>> 'i_version' on not only ext4 but also the other filesystem.
>>>>
>>>> SB_I_VERSION is a kernel internal flag.  XFS doesn't have an i_version
>>>> mount option.
>>>
>>> It probably *should* be a kernel internal flag, but it seems to work as
>>> a mount option too.
>>
>> Not on XFS AFAICT:
>>
>> [600280.685810] xfs: Unknown parameter 'i_version'
> 
> Yeah, because the mount option is 'iversion', not 'i_version'.  Even if

unless you're ext4:

{Opt_i_version, "i_version"},

ok "iversion" is what mount(8) takes and translates into MS_I_VERSION (thanks Darrick)

# strace -vv -emount mount -oloop,iversion fsfile mnt
mount("/dev/loop0", "/tmp/mnt", "xfs", MS_I_VERSION, NULL) = 0

FWIW, mount actually seems to pass what it finds in /proc/mounts back in on remount for ext4:

# strace -vv -emount mount -o remount mnt
mount("/dev/loop0", "/tmp/mnt", 0x55bfcbdca150, MS_REMOUNT|MS_RELATIME, "seclabel,i_version,data=ordered") = 0

but it still looks unhandled on remount.  Perhaps if /proc/mounts exposed
"iversion" (not "i_version") then mount -o remount would DTRT.

-Eric

> you were going to expose the flag state in /proc/mounts, the text string
> should match the mount option.
> 
>> so we can't be exporting "mount options" for xfs that aren't actually
>> going to be accepted by the filesystem.
>>
>>> By coincidence I've just been looking at a bug report showing that
>>> i_version support is getting accidentally turned off on XFS whenever
>>> userspace does a read-write remount.
>>>
>>> Is there someplace in the xfs mount code where it should be throwing out
>>> SB_I_VERSION?
>>
>> <cc xfs list>
>>
>> XFS doesn't manipulate that flag on remount.  We just turn it on by default
>> for modern filesystem formats:
>>
>>         /* version 5 superblocks support inode version counters. */
>>         if (XFS_SB_VERSION_NUM(&mp->m_sb) == XFS_SB_VERSION_5)
>>                 sb->s_flags |= SB_I_VERSION;
>>
>> Also, this behavior doesn't seem unique to xfs:
>>
>> # mount -o loop,i_version fsfile test_iversion
>> # grep test_iversion /proc/mounts
>> /dev/loop4 /tmp/test_iversion ext4 rw,seclabel,relatime,i_version 0 0
>> # mount -o remount test_iversion
>> # grep test_iversion /proc/mounts
>> /dev/loop4 /tmp/test_iversion ext4 rw,seclabel,relatime 0 0
>> # uname -a
>> Linux <hostname> 5.7.0-rc4+ #7 SMP Wed Jun 10 14:01:34 EDT 2020 x86_64 x86_64 x86_64 GNU/Linux
> 
> Probably because do_mount clears it and I guess xfs don't re-enable
> it in any of their remount functions...