linux-ext4 - Re: [PATCH V1 7/9] fs/ext4: Make DAX mount option a tri-state

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Date:   Thu, 14 May 2020 13:25:53 +0200
From:   Jan Kara <jack@...e.cz>
To:     ira.weiny@...el.com
Cc:     linux-ext4@...r.kernel.org,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        Al Viro <viro@...iv.linux.org.uk>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>, Jeff Moyer <jmoyer@...hat.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V1 7/9] fs/ext4: Make DAX mount option a tri-state

On Wed 13-05-20 23:53:13, 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_MOUNT2_DAX_NEVER and set
> it and EXT4_MOUNT_DAX_ALWAYS appropriately.
> 
> We also force EXT4_MOUNT2_DAX_NEVER 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>
> 
> ---
> Changes from RFC:
> 	Combine remount check for DAX_NEVER with DAX_ALWAYS
> 	Update ext4_should_enable_dax()

...

> @@ -2076,13 +2079,32 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
>  		}
>  		sbi->s_jquota_fmt = m->mount_opt;
>  #endif
> -	} else if (token == Opt_dax) {
> +	} else if (token == Opt_dax || token == Opt_dax_str) {
>  #ifdef CONFIG_FS_DAX
> -		ext4_msg(sb, KERN_WARNING,
> -		"DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
> -		sbi->s_mount_opt |= m->mount_opt;
> +		char *tmp = match_strdup(&args[0]);
> +
> +		if (!tmp || !strcmp(tmp, "always")) {
> +			ext4_msg(sb, KERN_WARNING,
> +				"DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
> +			sbi->s_mount_opt |= EXT4_MOUNT_DAX_ALWAYS;
> +			sbi->s_mount_opt2 &= ~EXT4_MOUNT2_DAX_NEVER;
> +		} else if (!strcmp(tmp, "never")) {
> +			sbi->s_mount_opt2 |= EXT4_MOUNT2_DAX_NEVER;
> +			sbi->s_mount_opt &= ~EXT4_MOUNT_DAX_ALWAYS;
> +		} else if (!strcmp(tmp, "inode")) {
> +			sbi->s_mount_opt &= ~EXT4_MOUNT_DAX_ALWAYS;
> +			sbi->s_mount_opt2 &= ~EXT4_MOUNT2_DAX_NEVER;
> +		} else {
> +			ext4_msg(sb, KERN_WARNING, "DAX invalid option.");
> +			kfree(tmp);
> +			return -1;
> +		}
> +
> +		kfree(tmp);

As I wrote in my reply to previous version of this patch, I'd prefer if we
handled this like e.g. 'data=' mount option. I don't think any unification
in option parsing with XFS makes sence and I'd rather keep consistent how
ext4 handles these 'enum' options.

								Honza

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