Subject: Re: [PATCH] tune2fs: check whether dev is mounted or in use before
 setting
To:     Theodore Ts'o <tytso@mit.edu>
CC:     Ext4 Developers List <linux-ext4@vger.kernel.org>,
        <adilger@whamcloud.com>, Jan Kara <jack@suse.cz>,
        linfeilong <linfeilong@huawei.com>,
        wuguanghao <wuguanghao3@huawei.com>,
        zhanchengbin <zhanchengbin1@huawei.com>, <libaokun1@huawei.com>
References: <8babc8eb-1713-91c9-1efa-496909340a6f@huawei.com>
 <20230318162421.GB11916@mit.edu>
From:   Zhiqiang Liu <liuzhiqiang26@huawei.com>
Message-ID: <138552dd-c323-f9f9-9b26-84346527fd05@huawei.com>
Date:   Sun, 19 Mar 2023 13:44:57 +0800
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On 2023/3/19 0:24, Theodore Ts'o wrote:
> On Sat, Mar 18, 2023 at 11:36:03AM +0800, Zhiqiang Liu wrote:
>> From: Zhiqiang Liu <liuzhiqiang26@huawei.com>
>>
>> tune2fs is used to adjust various tunable filesystem pars, which
>> may conflict with kernel operations. So we should check whether
>> device is mounted or in use at the begin similar to e2fsck and mke2fs.
>>
>> Of course, we can ignore this check if -f is set.
> 
> Tune2fs is designed to work on mounted file systems.  There are
> individual checks for those changes which can not be safely done on
> mounted file systems, but most changes are safe to do on mounted file
> systems.
> 
Thanks for your reply.

Does quota setting is safely done on mounted or busy filesystems?

We have met a problem as follows,
# mkfs.ext4 /dev/sdd
# mount /dev/sdd /test
			# /test mountpoint is used in other namespace
# umount /dev/sdd
# tune2fs -O project,quota /dev/sdd
# mount -o prjquota /dev/sdd /test
# mount | grep sdd
/dev/sdd on /test type ext4 (rw,relatime,seclabel,prjquota)
# quotaon -Ppv /test
quotaon: Mountpoint (or device) /test not found or has no quota enabled

Here, tune2fs only check whether /test is mountted when setting project,quota,
it does not check whether /test is busy (/test is mounted in other namespace).
Users will be very confused about why prjquota does no take effect.

Should we check whether mountpoint is busy when setting quota?

Zhiqiang Liu.

> Cheers,
> 
> 					- Ted
> 
> .
>