linux-ext4 - Re: [PATCH V4 7/8] fs/ext4: Introduce DAX inode flag

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Message-ID: <20200522114848.GC14199@quack2.suse.cz>
Date:   Fri, 22 May 2020 13:48:48 +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>,
        Eric Biggers <ebiggers@...nel.org>,
        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 V4 7/8] fs/ext4: Introduce DAX inode flag

On Thu 21-05-20 12:13:12, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> Add a flag to preserve FS_XFLAG_DAX in the ext4 inode.
> 
> Set the flag to be user visible and changeable.  Set the flag to be
> inherited.  Allow applications to change the flag at any time with the
> exception of if VERITY or ENCRYPT is set.
> 
> Disallow setting VERITY or ENCRYPT if DAX is set.
> 
> Finally, on regular files, flag the inode to not be cached to facilitate
> changing S_DAX on the next creation of the inode.
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>

...

> @@ -303,6 +318,16 @@ static int ext4_ioctl_setflags(struct inode *inode,
>  	unsigned int jflag;
>  	struct super_block *sb = inode->i_sb;
>  
> +	if (ext4_test_inode_flag(inode, EXT4_INODE_DAX)) {
> +		if (ext4_test_inode_flag(inode, EXT4_INODE_VERITY) ||
> +		    ext4_test_inode_flag(inode, EXT4_INODE_ENCRYPT) ||
> +		    ext4_test_inode_state(inode,
> +					  EXT4_STATE_VERITY_IN_PROGRESS)) {
> +			err = -EOPNOTSUPP;
> +			goto flags_out;
> +		}
> +	}

The way this check is implemented wouldn't IMO do what we need... It
doesn't check the flags that are being set but just the current inode
state. I think it should rather be:

	if ((flags ^ oldflags) & EXT4_INODE_DAX_FL) {
		...
	}

And perhaps move this to a place in ext4_ioctl_setflags() where we check
other similar conflicts.

And then we should check conflicts with the journal flag as well, as I
mentioned in reply to the first patch. There it is more complicated by the
fact that we should disallow setting of both EXT4_INODE_DAX_FL and
EXT4_JOURNAL_DATA_FL at the same time so the checks will be somewhat more
complicated.

								Honza

> +
>  	/* Is it quota file? Do not allow user to mess with it */
>  	if (ext4_is_quota_file(inode))
>  		goto flags_out;
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR