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

From: Ira Weiny <ira.weiny@intel.com>
To: Jan Kara <jack@suse.cz>
Cc: linux-ext4@vger.kernel.org,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	"Theodore Y. Ts'o" <tytso@mit.edu>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Dan Williams <dan.j.williams@intel.com>,
	Dave Chinner <david@fromorbit.com>,
	Christoph Hellwig <hch@lst.de>, Jeff Moyer <jmoyer@redhat.com>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH V1 7/9] fs/ext4: Make DAX mount option a tri-state
Date: Thu, 14 May 2020 07:27:37 -0700	[thread overview]
Message-ID: <20200514142737.GD2140786@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <20200514112553.GH9569@quack2.suse.cz>

On Thu, May 14, 2020 at 01:25:53PM +0200, Jan Kara wrote:
> On Wed 13-05-20 23:53:13, ira.weiny@intel.com wrote:
> > From: Ira Weiny <ira.weiny@intel.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@intel.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.

Ok...  I'm sorry I'll change this.  Thanks for all the reviews!
Ira

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