linux-kernel - Re: [PATCH RFC 5/8] fs/ext4: Make DAX mount option a tri-state

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Message-ID: <20200415125147.GH6126@quack2.suse.cz>
Date:   Wed, 15 Apr 2020 14:51:47 +0200
From:   Jan Kara <jack@...e.cz>
To:     ira.weiny@...el.com
Cc:     linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jeff Moyer <jmoyer@...hat.com>,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH RFC 5/8] fs/ext4: Make DAX mount option a tri-state

On Mon 13-04-20 21:00:27, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> We add 'always', 'never', and 'inode' (default).  '-o dax' continue to
> operate the same.
> 
> Specifically we introduce a 2nd DAX mount flag EXT4_MOUNT_NODAX and set
> it and EXT4_MOUNT_DAX appropriately.
> 
> We also force EXT4_MOUNT_NODAX if !CONFIG_FS_DAX.
> 
> https://lore.kernel.org/lkml/20200405061945.GA94792@iweiny-DESK2.sc.intel.com/
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>

...

> @@ -2303,6 +2325,13 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb,
>  	if (DUMMY_ENCRYPTION_ENABLED(sbi))
>  		SEQ_OPTS_PUTS("test_dummy_encryption");
>  
> +	if (test_opt2(sb, NODAX))
> +		SEQ_OPTS_PUTS("dax=never");
> +	else if (test_opt(sb, DAX))
> +		SEQ_OPTS_PUTS("dax=always");
> +	else
> +		SEQ_OPTS_PUTS("dax=inode");
> +

We try to show only mount options that were explicitely set by the user, or
that are different from defaults - e.g., see how 'data=' mount option
printing is handled.

>  	ext4_show_quota_options(seq, sb);
>  	return 0;
>  }
> @@ -5424,6 +5453,12 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
>  		sbi->s_mount_opt ^= EXT4_MOUNT_DAX;
>  	}
>  
> +	if ((sbi->s_mount_opt2 ^ old_opts.s_mount_opt2) & EXT4_MOUNT2_NODAX) {
> +		ext4_msg(sb, KERN_WARNING, "warning: refusing change of "
> +			"non-dax flag with busy inodes while remounting");
> +		sbi->s_mount_opt2 ^= EXT4_MOUNT2_NODAX;
> +	}
> +
>  	if (sbi->s_mount_flags & EXT4_MF_FS_ABORTED)
>  		ext4_abort(sb, "Abort forced by user");

I'd just merge this with the check whether EXT4_MOUNT_DAX changed.

								Honza

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR