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

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Date:   Wed, 21 Nov 2018 19:01:19 -0800
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Jean-Christophe Guillain <jcguillain@...uans.com>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: Metadata_csum is still enabled after trying to disable it.

On Wed, Nov 21, 2018 at 06:48:18PM +0100, Jean-Christophe Guillain wrote:
> 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 ?

Yes.

> How can I actually disable this parameter ?

I think you have to turn off the metadata_csum_seed feature, but tbh
tune2fs really shouldn't pester about !metadata_csum,metadata_csum_seed
filesystems...

--D

> Best regards,
> jC Guillain
> 
> 
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