linux-ext4 - Metadata_csum is still enabled after trying to disable it.

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Message-Id: <E1gPWbq-0006F7-IZ@eureka>
Date:   Wed, 21 Nov 2018 18:48:18 +0100
From:   Jean-Christophe Guillain <jcguillain@...uans.com>
To:     <linux-ext4@...r.kernel.org>
Subject: Metadata_csum is still enabled after trying to disable it.

Hi,

I see a strange behaviour when playing with the metadata_csum parameter of ext4.
(I use a Debian Stretch, with a kernel 4.9.0-8-amd64 #1 SMP Debian 4.9.110-3+deb9u6 (2018-10-08) x86_64 GNU/Linux)

How to reproduce :

* I enable metada checksum : OK
    root@...t# tune2fs -O metadata_csum /dev/my_vol
    tune2fs 1.43.4 (31-Jan-2017)
    Enabling checksums could take some time.
    Proceed anyway (or wait 5 seconds) ? (y,N) y

* I check : Checksum enabled
    root@...t# tune2fs -l /dev/my_vol
    tune2fs 1.43.4 (31-Jan-2017)
    Filesystem volume name:   <none>
    [...]
    Journal backup:           inode blocks
    Checksum type:            crc32c
    Checksum:                 0xb0e3a180

* I change filesystem UUID : OK
    root@...t# tune2fs -U random /dev/my_vol
    tune2fs 1.43.4 (31-Jan-2017)
    Setting UUID on a checksummed filesystem could take some time.
    Proceed anyway (or wait 5 seconds) ? (y,N) y

* I disable metadata checksum : OK
    root@...t# tune2fs -O ^metadata_csum /dev/my_vol
    tune2fs 1.43.4 (31-Jan-2017)
    Disabling checksums could take some time.
    Proceed anyway (or wait 5 seconds) ? (y,N) y

* I change filesystem UUID : It looks like metada checksum still is enabled
    root@...t# tune2fs -U random /dev/my_vol
    tune2fs 1.43.4 (31-Jan-2017)
    Setting UUID on a checksummed filesystem could take some time.
    Proceed anyway (or wait 5 seconds) ? (y,N) y

* I fsck the filesystem to see if it could fix this.
    root@...t# e2fsck -f /dev/my_vol
    2fsck 1.43.4 (31-Jan-2017)
    Pass 1: Checking inodes, blocks, and sizes
    Pass 2: Checking directory structure
    Pass 3: Checking directory connectivity
    Pass 4: Checking reference counts
    Pass 5: Checking group summary information
    /dev/my_vol: 16303/3932160 files (0.9% non-contiguous), 1829950/15728640 blocks

* I check : metadata checksum looks like disabled
    root@...t# tune2fs -l /dev/my_vol tune2fs 1.43.4 (31-Jan-2017)
    Filesystem volume name:   <none>
    [...]
    Journal backup:           inode blocks

* I change filesystem UUID : It looks like metada checksum still is enabled
    root@...t# tune2fs -U random /dev/my_vol
    tune2fs 1.43.4 (31-Jan-2017)
    Setting UUID on a checksummed filesystem could take some time.
    Proceed anyway (or wait 5 seconds) ? (y,N) y

Is it a bug ?
How can I actually disable this parameter ?

Best regards,
jC Guillain


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